Science Makes Sense Week 38:Noble gases

June 13, 2016

I remember when I was young, I liked stretching on a black sofa almost upside-down and reading a book. My mother would come and implore me to go out and I would be oblivious to her presence. “Why aren’t you reacting? It is as if you are in another world!”, she would remark in dismay.
Sometimes, when I look at the last group in the Periodic Table, the Noble Gases, I wonder if they too belong in another world. Helium,He, neon, Ne, argon, Ar, krypton,Kr, xenon, Xe and radon, Rn are the six common noble gases. All these are obviously gases and the outer electronic structure is a stable octet, which is really a ns2 np6 configuration, where n=2 through 6. The exception is helium, which has a stable duplet or 1s2 structure.
One has already seen that the alkali and alkaline- earth elements try to lose one or two electrons to achieve the stable noble gas structure. In addition we have seen that the halogens gain an electron to have the outer stable electronic structure of noble gases. In fact, almost all elements in the periodic table gain or lose electrons during a chemical reaction to get to the stable electronic structure of these noble or inert gases. This also implies that the last group elements are not reactive. Now is that really a fact?
Till the early 60’s, scientists were talking about the stable octet/duplet rule to justify the non-reactive nature of these gases. Initially it was called Group 0 for this reason. In 1962 and 1963,scientists observed that some of the noble gases,like radon, krypton and xenon form different flourides. In addition, in 2006, scientists in Dubna, Russia, announced that the element 118, the next noble gas, was synthesized in 2002 and 2005 in a cyclotron.(Ref.1) A cyclotron is a high particle accelerator where subatomic particles like protons and electrons are in a magnetic and electrical field and can collide at high speeds with each other.(Ref.2)
Hence there are really 7 noble gases present and since some of them are not completely non-reactive, the noble gases group is now called Group 18 and not Group 0.(Ref.1)
The noble gases are all colorless, odorless, tasteless, non-flammable gases. They also happen to be mono-atomic gases, ie, they exist as individual atoms rather than di- or poly- atomic molecules.(Ref.3) They were originally called inert or rare gases. They are neither inert(since we know some of them react with flourine to form compounds) nor rare, because several of them are found in abundance on earth.(Ref.1) Yet the word’noble’ is appropriate, since certain elements like gold or platinum are also considered ‘noble metals’ because of their reluctance to undergo chemical reactions easily.(Ref.1)
How abundant are these noble gases? It is noted that their abundance decreases with increase in atomic weight, with He being the most abundant while there are only three molecules of element 118! Most of the noble gases are present in the earth’s atmosphere, except for helium, radon and are recovered from the air by obtaining them as liquids and conducting fractional distillation to separate them.(Ref.1) (Fractional distillation is a technique whereby different liquids can be distilled/condensed using differences in their boiling points, to collect each substance separately.)
Actually both radon and even helium are by-products of radioactive decay. After the discovery of radium by the Curies, German physicist became fascinated with radium and discovered a gas that it emitted and he called it ‘radium emitting; he discovered the new element, radon. The breakdown of radium as well as uranium can lead to the production of helium ions as well.(Ref.3)
The noble gases are used in many daily and specialized applications. Helium as we already know has been used in the filling of balloons, for large airships and for children. Helium is also used by divers not for buoyancy but to prevent “the bends” a condition when nitrogen bubbles in the blood as a diver comes up to the surface. Helium is extensively used in the field of cryogenics which is low-temperature science. Neon is best known for its use in neon signs, neon glow lamps are used to indicate on/off signs in electronic instrument panels and in early televisions. Even though radon is considered a hazard it has its uses in earthquake detection, leaks, measuring flow rates. Paleontologists, who study the distant past as well as geologists use argon dating to study volcanic layers, fossils etc. Krypton is mixed with argon in the manufacture of windows with high thermal efficiency, used in lasers as well as halogen headlights. Along with xenon, especially because of its lower cost, krypton has been used as a fuel in space.

As one can see, these noble gases are not so quiet and inert as they seem.
Activities for Middle School Teachers:
Have a discussion with students about how certain words like ‘inert’, ‘rare’ to describe the Group 18 gases is really not accurate. Look at the history of the ‘phlogiston’ theory and how the burning/oxidation theory was modified with further experiments in science. Look at the history of the atomic models and see how those models evolved with time and more knowledge. How did the invention of new instruments in the laboratory aid these developments? Compare the evolution of ideas in chemistry, physics with say, social sciences and psychology.
Nuggets of Information:
In 1868, a French astronomer named Pierre Janssen (1824-1907)came to India to observe a total solar eclipse. Using a spectroscope, an instrument for analyzing the spectrum of light emitted by an object, Janssen was able to show a yellow line in the spectrum, never seen before, which seemed to indicate the presence of a previously undiscovered element. He called it “helium” after the Greek god Helios, or Apollo, whom the ancients associated with the Sun.(Ref.3)
Helium is remarkable since it only liquefies close to absolute zero(-272 degrees celcius); that makes it very difficult to liquefy from air.(Ref.3)
Almost all the noble gases have derived their names from the Greek language. Neon comes from the word ‘neos’ which means new,argon from ‘argos'(inactive), krypton from kryptos,(hidden) and xenon from the word ‘stranger’.(Ref.3)
Superman’s kryptonite is an imaginary substance and has no relationship with the noble gas krypton.(Ref.3)
The discovery of radon starting with the element radium was the first clear proof of one element being transformed to another element through radioactive decay. (Ref.3)
Within the atmosphere,, argon is considered the most ‘abundant’ of these gases, about 0.93%.(Ref.3)
Until 1988, most Americans had no knowledge of the existence of radon, when the EPA(Environmental Protection Agency) released a report indicating the harmful effects of radon in homes. From the 80s through the 90s radon detector sales boomed; even today when a house is sold, radon levels need to be checked. This is especially needed if a house has been weather-sealed to improve heating and cooling.(Ref.3)
Chinese scientists made an interesting discovery in the 1960s. Radon levels in groundwater increased significantly before an earthquake. These scientists monitor radon levels to predict earthquakes.(Ref.3)

Science Makes Sense-Week 37: The alkaline earth metals

May 17, 2016

My grandmother was very particular that all the grandchildren who came to visit her had milk at night. She would stand with a big warm container of milk and insist that we all had a small glass before we went to bed. My younger sister hated this white liquid and would swallow it with great difficulty. Even now she dislikes the taste of milk but gets her calcium from plenty of yogurt and dietary supplements.
Calcium,Ca, is one of the alkaline-earth metals along with Beryllium,Be, Magnesium,Mg,Strontium,Sr, Barium,Ba and Radium, Ra. (Radium was covered last week) All are metals and form Group 2, next to the Group 1 alkali-metals in the Periodic Table. Like the alkali-metals, they are soft, silvery-white metals, reactive (but not as reactive as the alkali-metals) and never found as an element in the natural state. And again, like them, they glow with characteristic colors and are distinguished by the flame test. Unlike the alkali-metals which have 1 electron in the ‘s’ shell, they have two electrons in the ‘s’ shell.(Ref.1)
Some of the alkaline-earth metals except radium and beryllium were discovered by the English Chemist, Sir Humphrey Davy in the early part of the 19th century. Around this period, Sir Davy also discovered two of the alkali-earth metals, potassium and sodium.(Ref.1)
The alkaline-earth metals react easily with water to release hydrogen gas and form the metal hydroxide. Many of them react with oxygen to form oxides. In nature they are usually found as sulfates and carbonates.(Ref.1)
The most abundant of these metals is calcium, Ca. It is the fifth most abundant element in the earth’s crust as well as in the human body. Magnesium, Mg is the seventh most abundant element in the human body, whereas Ba, Be nor Ra, St are found in the body, since the first two are poisonous while radium is radioactive; meanwhile strontium is only present as 360 ppm on the earth’s crust.(Ref.1)
Beryllium is used in the health-care industry, (besides being found in precious stones)in X-ray tubes as well as in alloys for specialized electrical connections and for high-temperature uses.
Besides magnesium being important as a digestive aid and formerly used for asbestos, today it is used in the manufacture of fertilizers. Because of its property to burn in oxygen with a brilliant flame,in World War 1, magnesium was used as flares, tracer bullets and incendiary bombs. Later in World War 2, it was used to build aircraft and military equipment. Today it is used with other metals to manufacture catcher’s masks, skis, race cars and even horseshoes.(Ref.1)
Calcium has been used in buildings from ancient times. Steel, glass, paper and metallurgical industries use slaked lime(calcium hydroxide, Ca(OH)2). Acetylene used for welding is made by reacting calcium carbide(CaC2) with water. Calcium compounds are also used as a bleach, fertilizer and sometimes to melt ice on roads.
Even though strontium is not as abundantly available it still has several uses. Like magnesium, it is used for flares, tracer bullets and also for fireworks- having a brilliant crimson color. It is also used in color television picture tubes, to refine zinc and combined with iron, strontium is used to make magnets.(Ref.1)
Barium compounds are used extensively in health care applications: in enemas and also to coat inner linings of intestines so doctors can examine the patients’ digestive system.(Ref.1)
The alkaline-earth elements are used in a wide variety of ways; they are not just known for calcium and strong bones.
Activities for Middle School Teachers:
Study the boiling and melting points of the alkaline- earth elements. Is there a correlation between them and their atomic numbers as in the case of alkali-metals?
Helium,, He, has two electrons in its outermost ‘s’ shell, why then does it not behave like an alkaline-earth metal? Let the students discuss this with the teacher.
Nuggets of Information:
Beryllium is found in emeralds and aquamarines as a compound of beryllium and alumino-silicate and is called beryl.(Ref.1)
Magnesium is found as dolomite or magnesite which are carbonates of magnesium, MgCO3. (Ref.1)
Calcium is found mostly as limestone and as dolomite (calcium carbonate, CaCO3) and also as gypsum(calcium sulfate, CaSO4)
Strontium was initially discovered by Adair Crawford, an Irish Chemist in the late 18th century in witherite; it is also found in strontianite(strontium carbonate, SrCO3) and in celestite( strontium sulfate,SrSO4)(Ref.2)
Barium is found as barite(BaSO4,barium sulfate) or witherite(BaCO3,barium carbonate)(Ref.3)
Magnesium sulfate, also known as Epsom salts has been long known for their medicinal value,mainly in Epsom salts springs. It has also been used for the treatment of eclampsia, a condition that causes seizures in pregnant women.(Ref.1)
Salts of magnesium are used as a powerful laxative(Ref.1) but magnesium hydroxide,Mg(OH)2 also known an milk of magnesia is the preferred laxative.(Ref.4)
One of the most controversial uses of magnesium has been in asbestos, as a fire retardant. It is a silicate of magnesium with the formula Mg3Si2O5(OH)4. This had been used for commercial purposes 95% of the time.(Ref.5) For years it was used as a flame-retardant till it was found to be cancer-causing and had to be removed from many buildings. In spite of this, magnesium as an element is important in the health of living organisms.(Ref.1)
Magnesium plays a critical role in chlorophyll, the green pigment in plants that gets its energy from sunlight.(Ref.1)
More than magnesium, calcium is vital for living beings and is present in leaves, teeth, bones, shells and coral.(Ref.1)
We all know that calcium is essential for bone-building but it also plays an integral part in almost every cell in the body especially in the growth of muscles, the nervous system as well as the heart.(Ref.6)
Osteoporosis is caused by a loss in bone density and can be prevented by eating foods high in calcium like green vegetables and dairy products.(Ref.1)
An isotope of strontium, Sr 90, is radioactive and is a by-product of nuclear testing from the ’40’s. Once, during testing, this isotope fell to earth, coated grass and was ingested by cows. The milk from these cows was drunk by many children when the Sr 90 got into their teeth and gums causing many health problems. In the 60’s atmospheric nuclear testing was stopped. Strontium 90 affects production of red blood cells and could lead to death.(Ref.1)
Prior to receiving X-rays, patients drink a chalky barium sulfate,BaSO4 solution which absorbs radiation and adds contrast to the image.(Ref.1)

Science Makes Sense-Week 36: Chemistry and Social Justice-radiation, radium girls.

May 9, 2016

I remember when I was six or seven, my uncle came to visit us in the evening when we had a power cut in India and had no electricity. Everything turned pitch dark but I could see my uncle’s watch gleaming green in the dark! “Why is that happening? Do you have a magic watch?” I exclaimed. ” No magic, it is a glow-in-the-dark watch,” he responded. I was fascinated and learned years later that it was a radium watch. The dials had been painted with a salt containing radium.
Today we shall look closely at the discovery and use of one of the radioactive elements, radium (mention others in nuggets) and the terrible results of exposure due to ignorance and careless/negligent planning.
Radium was discovered by Pierre and Marie Curie in 1897 along with Polonium.(Ref.1) Pierre and Marie Curie were unaware of the dangers in the late 19th century/ early 20th century about nuclear reactions.
Most chemical reactions occur through transference/sharing of electrons, those very tiny particles that circle far away from the nucleus of an atom of any element. The nucleus is not touched in such reactions; however by the end of the 19th century, scientists were entering the realm of nuclear reactions. The nucleus is where the protons and neutrons are situated. The energy released when the nucleus is attacked, is several times that of a chemical reaction. Such attacks can be man-made as in nuclear reactors, and the explosion of atomic bombs, but radioactive elements that naturally decay can also cause nuclear reactions.
In fact Henri Becquerel was the first to observe mysterious radiation in uranium compounds and Maria and Pierre Curie did measurements on the amount of radiation emitted.(Ref.1) It is important to note that elements like technitium,Tc, prometheium, Pm as well as elements starting with polonium Po, all the way to the end of the Periodic Table exhibit radioactivity. In other words all the elements from atomic number 84 to atomic number 105 are radioactive, besides technitium and prometheium. Some of these elements are not too stable having very short half-lives.(Ref.2,3) Half life for an element is the time needed for half the mass of the element to decay.
The radioactive decay of elements leads to three kinds of ionizing radiation: alpha and beta particles as well as gamma radiation. Alpha particles consist of a pair of protons and neutrons, viz., it is a Helium ion. This is the least dangerous as far as radiation effects go, since they do not penetrate very deeply into clothing or skin. However, once ingested or inhaled through water or food sources, they could become carcinogenic and ultimately lead to lung cancer and other cancers. Beta particles are electrons that move very quickly; being 8000 times smaller than an alpha particle, this allows them to penetrate clothing and skin very easily. External exposure leads to burns and tissue damage and ingested/inhaled through water/food contamination could lead to serious health problems. Gamma rays are the most dangerous, these are fast-moving photons with no mass , passing easily through all body tissues and bone marrow causing extensive damage to the body and death based on amount/duration of exposure.(Ref.4)
While Marie and Pierre Curie may have been ignorant of the dangers of radium’s radioactivity, years later, many women were dangerously exposed to radium in U.S.factories where they were making radium watches and clocks. Referred to as the “radium girls” in Waterbury,Connecticut, Orange,New Jersey and in Ottawa, Illinois, young girls worked in factories and painted radium mixed as a paint with zinc sulfide, on dials of watches and clocks.(Ref.5) The managers, wanted them to lick the brushes so they were pointed to do the fine painting on the dials. Some of these girls even painted their buttons and finger nails to glow in the dark unaware of the terrible consequences. Initially because of ingesting alpha particles from the radioactive radium, they had terrible pains near the teeth and jaw, but eventually developed swelling and total destruction of the jaw and finally death in some cases. In Orange, new Jersey, 4 dial painters died and 8 were very ill. Dial painters there filed a suit in March of 1925 and following that workers no longer used their mouths to lick and point the brushes, they started wearing rubber gloves and use fume hoods after 1927. No more cases of cancers in dial painters were officially blamed on radiation. But the damage had been done.(Ref.5,6,7)
Years later, the suffering of the Radium girls led to safety measures for World War II atomic bomb workers.(Ref.5) Aah! But at what cost??
Activities for Middle School Teachers:
Teachers need to discuss how loosely and incorrectly certain words are used in daily life. The most common errors are made when the word ‘chemical’or ‘radiation’ is used, for example. All chemicals, radiation are considered harmful whereas water is also a chemical and electromagnetic radiation encompasses visible light. Let students research these words in science and understand the variation in meaning depending on context. Also, let students find other words in science that are mis-understood or partially explained by the non-scientific community.
Teachers should collaborate with Language Arts teachers and see if the word ‘synecdoche’ could be used to describe the incorrect usage of certain scientific words. (This word is a part of speech akin to a metaphor or simile; it means when a word is used to describe part of what it actually means)
Nuggets of Information:
Marie Curie’s notebooks and even her cookbook are so radioactively charged that they can only be viewed through lead screens today.(Ref.8)
Henri Becquerel received a burn carrying radium-rich barium chloride in his waist-pocket. Pierre Curie suggested that radium could be used for cancer therapy and in the 20’s it was used to treat some forms of skin cancer. In fact radium was touted as a cure for hypertension, diabetic pain, arthritis, gout and even for tuberculosis of the lung. Today, however radium is not used for any of this, but some research is underway to study its use to relieve intractable pain.(Ref.9)
Because of prolonged exposure to uranium, polonium and especially radium, Marie Curie succumbed to anemia related to radiation in bone marrow.(Ref.4)
The Geiger Counter was invented in 1928 and is used to measure radioactivity levels in many elements.(Ref.9)
It is important to note that all forms of radiation are not harmful to humans; e.g., electromagnetic radiation includes visible light. Also many man-made products like televisions,smart phones, microwave ovens emit radiation that are not dangerous and the danger varies with strength and length of exposure.(Ref.4)
There were 30 women in Connecticut, 35 women in Illinois and 41 women in New Jersey who died because of being dial painters (Radium Girls) in the 1920’s.(Ref.5)
Alexander Litvinenko, a former KGB officer died 3 weeks after ingesting a cup of tea containing Polonium 210.(Ref.8)
6.Clark, Claudia, Radium Girls,(University of North Carolina Press, 1997)
7.Mullner, Ross, Deadly Glow,( American Public Health Association, 1999)

Science Makes Sense-Week35:Organic Chemistry,Benzenoid aromatic compounds

May 2, 2016

Every year my mother would clean her silk saris by washing them in mild soap, getting them ironed and stack them in the cupboard with a few moth balls. So every time I would open the cupboard to wear her saris I would smell the odor of moth balls and hope it did not cling to me! Moth balls originally contained naphthalene which is a benzenoid compound and we shall look at a few of these today.
Benzenoid compounds contain the benzene ring and last time we had a chance to look at the simplest of these, benzene. The structure of benzene was discovered almost simultaneously by Loschmidt and Kekule around the mid-19th century,(both German scientists) as a six-membered cyclic hydrocarbon containing 6 carbon and 6 hydrogen atoms with alternating double bonds. But it was Kekule who modified the structure to one where the oscillation of the double bonds gave two equivalent structures in rapid equilibrium. Then in 1931, Linus Pauling suggested that benzene had a single structure that was a resonance hybrid of the two Kekule structures.(Ref.1)
Benzene is a colorless volatile liquid with a characteristic strong odor and is the starting point for the manufacture of many aromatic compounds including aniline, phenols.(Ref.1)
Modern bonding models (valence bonding and molecular orbital theory) explain the stability of the benzene due to the delocalization of the six electrons. This delocalization refers to the attraction of an electron by all six carbon atoms instead of one or two, making benzene very stable. Unlike other unsaturated hydrocarbons, the hydrogenation and oxidation of benzene is a slow process. Most reactions of benzene are electrophilic aromatic substitution where the ring is intact and replacement of hydrogen occurs. Such reactions are important in forming derivatives of benzene.(Ref.1)
Benzene is present/manufactured in oil refineries, rubber and shoe manufacturing as well as in gas stations and firefighting.(Ref.2). Benzene has been documented as a cancer-causing agent and the results of exposure are mentioned in Nuggets.
The next aromatic compound we will study is toluene, also known as methyl benzene where one of the hydrogen atoms is replaced by a methyl(CH3)group. The odor is similar to benzene and it is usually a stable compound unless subjected to high temperatures. It is one of the by-products of gasoline production, but most of the benzene is manufactured starting with toluene. Toluene is used in the manufacture of adhesives, rubber, laboratory paints, pesticides and pharmaceuticals.(Ref.3)
The third set of aromatic compounds are called phenols. When a hydroxyl group, -OH group is attached to a carbon atom of a benzenoid ring, the compound is called a phenol. Phenols are similar to alcohols; however the hydrogen bond is stronger so they are more soluble in water than alcohols and have a higher boiling point. They are usually colorless liquids or white solids and are toxic and caustic. Household products that contain phenols include disinfectants and mouthwash. In industry, phenol is the starting point for plastics, explosives,photography, dyes and aspirin.(Ref.4)
Finally we will look at the chemical composition of moth balls, another benzenoid compound. Today we use dichloro-benzene , but years ago naphthalene was used in the manufacture of moth balls. 2 fused rings of benzene comprise naphthalene with the formula C10H8. Naphthalene is a white, solid crystal and has a strong odor of coal tar. It can undergo electrophilic aromatic substitution. It can be hydrogenated partially to form 1,2,3,4 tetra hydro-naphthalene or completely to form decalin, C10H18. Both are used as low volatile solvents. Naphthalene is used as a fumigant/ pesticide mainly as well as in the production of dyes.(Ref.5)
We have looked at some of the benzenoid compounds; we use them in our everyday lives. Look at Nuggets to realize that some of these compounds are carcinogenic, some are explosives and some are also medicines. However, all are essential in our lives today.
Activities for Middle School Teachers:
Benzene has 3 different positions on the 6 carbon atoms: Immediately adjacent to the first carbon atom is called the ortho position, next to it is the meta position and directly opposite to it is the para position. Create the basic structure of benzene using kits available and then substitute different methyl groups in the different positions. Name them. Then change the hydrogen atom in the first position and insert an amine or hydroxyl group and repeat the process. Find out if such benzenoid compounds exist and what their names and uses are.
Also create structure of aspirin and salicylic acid. What is the latter used for?
Build structures for other pain relievers like ibuprofin and tylenol; find out their chemical/generic names as well.
Nuggets of Information:
Most of the benzene was originally obtained from coal tar, but from 1950, it has been derived from petroleum-based processes. More than half the benzene is converted to polystyrene, a common plastic. The steps to the conversion as as follows: benzene to ethyl benzene to styrene and then the polymer polystyrene.(Ref.1)
Benzene is one of the twenty most widely used chemicals in the United States. It is used mainly to manufacture plastics, lubricants, rubbers, dyes, detergents, drugs, and pesticides. You could breathe or ingest this aromatic compound easily in such environments.(Ref.2)
Benzene is present in cigarette smoke; in the presence of smokers we inhale benzene vapor. In fact, cigarette smoking causes half the exposure to benzene in the U.S.(Ref.2)
Benzene is a known carcinogen and workers who are constantly exposed to it are at a higher risk in developing leukemia and related cancers.(Ref.2)
Toluene derived its name from a tree in Colombia which has an aromatic extract called tolu balsam.(Ref.3)
TNT or tri-nitro-toluene is a known explosive and is made from nitric acid and toluene.(Ref.3)
Toluene is also used as an octane booster in gasoline. In biochemistry experiments toluene is used to rupture red blood cells for hemoglobin extraction.(Ref.3)
Phenols were the first surgical antiseptic used in 1865. Surgical amputations fell from 45% to 15% after using phenols. However, they were toxic as well.
A less toxic phenol like resorcinol, that contains two hydroxyl groups is often found in cough drops.(Ref.4)
Picric acid, which is trinitro phenol is used as a yellow dye as well as an explosive like TNT.(Ref.6)
Trace amounts of naphthalene are found in magnolias and certain kinds of deer.(Ref.5)
Naphthalene is considered to be a carcinogen; excessive inhalation or ingestion could cause hemolytic anemia.(Ref.7) Hemolytic anemia is caused by the destruction of red blood cells in the body.(Ref.8)
Aspirin, which is also known as methyl salicylate or 2 acetoxy-benzoic acid is an analgesic and is a non-steroidal anti-inflammatory agent. It is used usually for minor headaches and pains. Aspirin exhibits anti-coagulant properties(Ref.9) and therefore small doses are recommended every day to prevent heart attacks for some patients. It is an aromatic benzenoid compound.
Aniline, which is benzene with a hydrogen atom replaced by an amine _NH2 group is essential in the manufacture of dyes. It is responsible for the indigo color in blue jeans. Aniline is also used to make polymers like polyurethane, fungicides and herbicides. It is also used to make additives in rubber.(Ref.10)

Science Makes Sense-Week34: The other Alkali metals

April 25, 2016

Growing up, I was under the impression that potatoes were not good for you. Of course, my mother made them often and I enjoyed eating potatoes especially when fried. But I do remember the National Geographic feature on the merits of a potato and then I realized its significance as a great source of vitamins and minerals. A baked potato is high in potassium, an essential element needed in our bodies.
Potassium, like sodium, lithium, are part of Group 1A in the Periodic Table and are called alkali metals. They all have one lone electron in the ‘s’ orbital which makes them metals since they are willing to give it up to be a cation and have the outermost electronic structure of the closest neighbor, the inert noble gases. There are six alkali metals: lithium,Li, sodium,Na, potassium,K, rubidium,Rb, cesium,Cs and francium,Fr. Since the alkali metals are so reactive, it is never found in the elemental form in nature. Sir Humphrey Davy discovered Na and K in the early 19th century, while Li was discovered ten years later by a Swedish chemist. Later, Robert Bunsen, who invented the Bunsen burner, discovered Rb and Cs in 1860. Meanwhile, Fr was found in trace amounts and very little is known about its behavior.(Ref.1)
The alkali metals have a lot of properties similar to other traditional metals(copper, iron) like high conductivity, form cations easily, and are malleable and ductile. They have low ionization energy, i.e., the energy required to remove the outermost ‘s’ electron is not high. However, they are softer and silvery-white in color except for cesium which is yellow. In addition, their densities are lower than most metals and they have low boiling and melting points.(Ref.2)
They react very readily with oxygen when exposed to the air/oxygen to form oxides. Another important reaction is with water, when it vigorously reacts with it to form the hydroxides or alkalis, (which is responsible for its name) along with the release of hydrogen gas. This reaction is well documented in several videos to illustrate the increase in the rate of reaction as well as the increase in the intensity of the exothermic reaction as you go down this group of alkali metals. This particular video uses the same number of atoms of each alkali metal to react with the same amount of water each time and you will clearly see that the rate and intensity of the reaction increases significantly as you go down the group making cesium one of the most violent reactions to observe.(Ref.3)
The alkali metals react very easily with halogens to form the various halides.(Ref.1) No wonder sodium and potassium chlorides are found abundantly in nature.(Ref.4) In addition, the oxides of sodium and potassium react with carbon dioxide to form the various carbonates.(Ref.1) The alkali metals as hydroxides can easily react with nitric/nitrous and sulfuric acids to form the nitrates/nitrites and sulfates respectively.
Once we see the properties and reactions of alkali metals it is easy to see what are the salts of alkali metals available on the earth’s crust. Besides the fact that sodium chloride is found abundantly on the earth, we also find sodium carbonate, sodium nitrate(saltpetre), and sodium sulfate. Sodium nitrite is used extensively in the manufacture of gunpowder. The pulp and paper industry uses the hydroxide, carbonate and sulfates of sodium. Sodium sulfate is also used in the manufacture of cardboard and brown paper. Sodium carbonate is used in power companies to absorb sulfur dioxide which is a serious pollutant. NaOH, sodium hydroxide is one of the top ten industrial chemicals, while sodium bicarbonate, baking soda, NaHCO3, is invaluable in the food industry.(Ref.4)
Meanwhile most of the potassium is used as a fertilizer. KOH, potassium hydroxide is used for detergents,KClO3 potassium chlorate is needed in the manufacture of explosives while KBr, potassium bromide is essential in the photography industry.
The next three alkali metals, rubidium, cesium and francium are much less common. Rubidium is sometimes used for the treatment of depression, while cesium is mainly used in the manufacture of certain kinds of glass and radiation detection equipment. It is also used to make the atomic clock which will be explained more under Nuggets. But the main use of francium is in research, along with rubidium as well.(Ref.4)
The role of two of the alkali metals, sodium and potassium in our bodies cannot be underestimated. Both these alkali metals function as cations in our body; in other words they are charged particles that carry an electric current across our cells causing many physiological processes. It is important to maintain a balance of the sodium and potassium ions; ideally we need 3 times as much potassium as sodium in our bodies. Sadly we tend to consume more sodium containing products versus potassium containing products.(Ref.5) (More under Nuggets)
Even though the higher group alkali metals like rubidium, cesium and francium have limited uses, our lives would be cut short without the salts and hydroxides of the other alkali metals.
Activities for Middle School Teachers:
Look at the various halides formed by the alkali metals. Does it follow the multiplication principle? How about oxides and hydroxides? Do they follow that same principle? Why or why not?
How do we lose sodium from our bodies? What are the main sources of sodium in our diet? What are the common diseases associated with high sodium in our diets? Study the increase or decrease in these illnesses based on diet in various different countries over a 50-year period.
Nuggets of Information:
Sir Humphrey Davy who discovered two of the alkali metals, was born in Penzance, Cornwall, England. He was known as a wild man in the laboratory, often smelling and tasting the products of his experiments, which almost certainly shortened his life.(Ref.1)
The colors of the alkali metal salts are distinctive and are often used in the flame test to determine the cations of lithium, sodium and potassium. Chlorides of these cations are mixed with a little hydrochloric acid and placed on the blue upper part of a Bunsen flame. Lithium shows a crimson color, sodium the characteristic golden-yellow color and potassium has a lilac color.(Ref.6) Rubidium gives a dark red color, while cesium has a blue color.(Ref.4)
Potassium exists as sylvite, KCl on the earth’s crust.(Ref.4)
Both cations of potassium and sodium are found inside and outside a cell membrane in our bodies. The difference in the concentrations of these ions on each side of the cell membrane is called a membrane potential. The membrane potential uses the charge differences to conduct electricity between cells. This electricity then helps perform the work of contracting muscle, transmitting nerve impulses and maintaining the heartbeat. Processed foods increases the amount of sodium in our bodies, while foods like baked potatoes, prunes, spinach, bananas are good sources of potassium.(Ref.5)
Cesium has been used in the manufacture of atomic clocks that keep the best time. How does it work? Prior to 1964, the International Standard second was based on the orbital period of the earth. However, the cesium clock period was found to be much more stable. Using the 133 atomic mass of cesium, we focus on the lone electron outside the 54 electron core. This electron interacts with the nuclear spin and has an energy splitting called hyperfine structure. This splitting allows us to measure time with a precision of one second in 1.4 million years!(Ref.7)

Science Makes Sense-Week33: Lithium, the little pill that can

April 18, 2016

I shall never forget that call from my dear friend who needed me when her husband had a manic episode in the 80’s. Those were the days when I had barely heard of mental illnesses and least of all anything about manic depression/bipolar disorders. On a wintry morning, I drove over to her place to give her some company and comfort. He had been taken in restraints to the hospital. After years of being treated with ‘lithium’ he is the charming intelligent human being I knew before that incident. Now he is able to take care of his family and himself. This ‘lithium’ is chemically lithium carbonate which has been used successfully by several psychiatrists to treat mental illnesses like bipolar disorders.
Lithium,Li, is the first in the alkali metals and is one of the smallest atomic solids on the second period of the Periodic Table. As a metal it is highly reactive, and when added to water, reacts explosively to form the alkali lithium hydroxide.(Ref.1) In nature, lithium is found as a mixture of the two isotopes Li6 and Li7. Soft and silvery-white, Li has a low melting point but has a high specific heat. It seems to behave more like the alkaline-earth metals than the alkali-metals. (Ref.2)
Being very reactive, it does not usually exist as metallic Li but as the hydroxide, LiOH. It is one of the few elements to react easily with nitrogen to form a black nitrite. It reacts with hydrogen at higher temperatures around 500 degrees C to form lithium hydride, LiH. (Ref.2)
Uses: Main industrial uses of Li is as a lubricant grease thickener, in the glazing of pottery and to extend the life and storage of alkaline batteries. Lithium carbonate, Li(CO3)2, is used mainly to treat bipolar disorders. What is bipolar disorder or BD as it is often called? It is a mental condition that causes extreme shifts in a person’s energy levels. The person affected by this disease could be extremely agitated and ‘manic’ with racing thoughts for days/months and then come crashing down feeling major depression and guilt for their earlier actions. These mood shifts are very different from those that everyone else goes through, because people with BD could be totally impaired in their abilities to complete day-to-day tasks when suffering from this disorder.(Ref.3) When Li was discovered in 1817, it was used initially in the treatment of gout and physicians could tell that it was good as a mood stabilizer. The Australian psychiatrist, Dr. John Cade published the first paper on the use of lithium in the treatment of acute mania in 1949, but it was not until 1970 that the U.S.FDA approved it. (Ref.4)
The chlorides and bromides of Li are also used in absorbing humidity and hence in air-conditioning systems. Alloys of Li with cadmium, Cd, manganese, Mg, copper, Cu, are used in the manufacture of high-performance aircraft parts.(Ref.2)
Lithium’s role in the treatment of bipolar disorder or BD has undergone several modifications, but the key role is how it helps in reversing structural abnormalities in the brain/biochemical changes in the brain because of BD.
First Li ions help in decreasing second messenger systems in the brain, protects the nerves in the brain. BD patients have grey matter reductions especially in the medial frontal cortex and the hippocampus regions of the brain; Li ions once again help in reversing these effects. Overall, Li treatment(in the form of lithium carbonate/lithium ions) helps in maintaining the nerve plasticity of the brain. (Ref.5). It is almost as if this tiny metal ion is able to go around the brain and repair problems that cause BD in patients!
Activities for Middle School Teachers:
Students can study the ionic radii of elements in the first three periods and try to understand what the relative sizes of the cations and anions are. Is there a correlation with the increase/ decrease of radii based on the group or period ? Why?Create a graph for each of those periods using ionic radius of the element versus its atomic number. Is it a straight-line variation? How does the size of the lithium ion compare to other elemental ions?
If a model of the brain is available, the teacher needs to spend time talking about the different parts of the brain, including the hippo-campus and the frontal and medial cortices. What are the functions of the various parts of the brain?
Let the teacher spend time talking about several kinds of illnesses versus mental illnesses. Discuss how families are more open to talking about physical illnesses in loved ones versus mental illnesses. How are psychiatrists viewed in societies as opposed to other kinds of medical doctors? Is there a difference? Why?
Nuggets of Information:
Lithium is moderately abundant on the earth’s crust: 65ppm.(Ref.2)
In the U.S.,lithium is recovered from brine pools in Nevada while most commercial lithium is obtained from Chile.(Ref.2)
Compounds of Li and acetylene are used in the manufacture of Vitamin A.(Ref.2)
Bipolar disorder was officially known as manic depression in the 80’s.
The National Institute of Mental Health(NIMH)estimates 2.6% of U.S. adults suffer from BD, which is approximately 600,000 people in the U.S. More than 80% of these cases are classified as severe.(Ref.3)
Research has never indicated that bi-polar illness is because of lithium deficiency; rather that lithium carbonate acts as a mood stabilizer.(Ref.5)


Science Makes Sense-Week 32: Chemistry and Social Justice-Pesticides

April 11, 2016

Rachel Carson, wrote her book “Silent Spring” in 1962 and changed the way we looked at pesticides especially DDT. She may have been quite responsible to have initiated the environmental movement of today. But along with this movement, we continue to produce a lot of new pesticides that make your head spin when you do a search on the internet! So in the 21st century, when we talk of pesticides, it covers such an extensive area that we are not only looking at chlorinated organo-compounds like DDT but so many others including, to name a few, herbicides, fungicides, rodenticides as well.
Today we shall look at the chemical composition of many common pesticides, fungicides etc., their classifications and understand how it impacts humans and the environment. We will also touch on what are the alternatives to using synthetic pesticides.
The word “pesticide” is used to describe a substance (or mixture) that kills a pest, or it can prevent or minimize the damage that a pest causes. Examples of pests include insects, mice or other animals, unwanted plants (weeds), fungi, bacteria or viruses. Pesticides can also include any substance that is used to modify a plant. They are usually chemicals, but can also be made from natural materials such as animals, plants, bacteria, etc.(Ref.1)
The chemical families that most pesticides belong to are the following, organo-phosphates (organic compounds containing phosphorus), chlorinated hydrocarbons including DDT, carbamates (salts from carbamic acid which is really formic acid,HCOOH, with its free hydrogen replaced by an amine NH2 group). There are also thiocarbamates (‘thio’ is when an oxygen atom, O, is replaced by a sulfur,S, atom) and pyrethroids. Pyrethroids are benzenoid derivatives of pyrethrum which is obtained from chrysanthemums. Pyrethrum has the characteristic cyclopropane structure along with hydrocarbon chains with oxygen.(Ref.2)
How do all these different kinds of products broadly called insecticides affect humans and the environment?
Let us first look at its effects on humans. Starting with mild results like headaches and nausea, pesticides can also cause more serious and lasting health effects such as cancer, disruption of the endocrine system and reproductive harm. Disruption of the endocrine system means that the complex production of hormones is disturbed, resulting in infertility and babies born with birth defects. Children are especially susceptible to pesticides, because till the age of twelve, their brains are not fully developed and pesticides can impact the central nervous system.(Ref.4)
Pesticides affect the environment as well. Depending on whether the pesticide is water soluble or fat soluble, it can enter water bodies or get into fish and other aquatic life. Then when we as humans ingest them, we get health problems as well.(Ref.4)
In short, these are the harmful effects of all kinds of pesticides:
1. Pesticides damage ecosystems
2. They may damage/harm un-targeted animals(see Nuggets under ‘bioamplfication’)
3. Pesticides decrease biodiversity
4. Pesticides may cause a decline in populations and/or extinction of species
5. Pesticides “mess up” food chains/webs
6. Pesticides disrupt the ecosystems’ natural balance.
Knowing all this, organic farmers try going in one of two directions. The word ‘organic’ here has nothing to do with the definition in chemistry, it simply means the use of no pesticides or the absence of synthetic fertilizers. When they use no pesticides they allow crops to be spotted or eaten by a few pests and not look ‘perfect’ and allow weeds to coexist with crops/or do a lot of hand weeding. The alternative is to use naturally grown pesticides like pyrethrum that comes from chrysanthemums instead of synthetically applied pesticides and pheromone traps. Too much application of these pesticides can also lead to toxicity, so organic farming is a tricky business. But crop rotation, sprays and pheromone traps combined with minimal use of even naturally obtained pesticides by organic farmers will lead to less toxicity in humans and the environment.(Refs.5,6)
Activities for Middle School Teachers
Study the time-line of the different kinds of pesticides from the early 60’s to right now out there. How ‘natural’ are some of these pesticides? Take students on a field trip to organic farms and orchards. What alternative types of pest control is used here and how effective are they?
Look at the chemical structures of the different pesticides and note if there is a connection between type of chemical classification and specific use of the pesticide.
Nuggets of Information
Pesticides kill or repel insects and include bug sprays/repellants, baits, commercial and garden sprays, shampoos and moth balls. Herbicides kill weeds and unwanted plants. To achieve this we use weed killers, weed and feed fertilizers and tree stump treatments. Meanwhile, fungicides kills mould, mildew and other fungi. here we use commercial/ garden flower sprays,treated seeds and paint additives. Rodenticides kill all kinds of rodents using mouse and rat baits. Then we have disinfectants to kill bacteria, mould and mildew and use bleaches, ammonia, kitchen and bathroom cleaners as well as pool and spa cleaners. Finally, wood preservatives protect wood from insects and fungi and we use pressure-treated wood.
Broad Spectrum: Insecticides vary in what insects they kill. Some kill only a few types of insects. Then you could choose these insecticides when you wish to kill only one insect pest and not other beneficial insects in the area. Many insecticides are wide range killers or “broad spectrum”. Such pesticides are used when several different kinds of insects are a problem. One chemical can kill them all. No broad spectrum insecticide kills all insects; each varies as to the kinds of insects it can control.
Narrow Spectrum: While many insecticides are broad spectrum, a new group of insecticides attack the central nervous system, and are much more selective. The chitin inhibitors only affect animals with chitin in their exoskeleton (i.e. insects). (Chitin is the growth on an insect and inhibiting that growth can also kill the insect.) Growth regulators are even more specific. They affect certain groups of species that have a particular hormone. Finally, when we talk about pheromones, they are the most restrictive because they react with only one species or one sex of a single species.(Ref.3)
When grasshoppers, that are lower on the food chain eat pesticide-laden foods, they get the toxins in their systems. Then shrews, who are their predators, eat several grasshoppers and get more of the toxins in them. Owls in turn, eat several shrews and get even more toxins in them. This process is called Bioamplification. Remember, there could be a decrease in the owl population which may die because of so many toxins in their systems, leading to an increase in shrew population and a consequent decrease in grasshoppers. All this leads to a complete change in the balance of species.
Cesar Chavez was a fighter for better working conditions for the California grape and lettuce pickers. He gave the famous ‘wrath of grapes’ speech in the 80s after twenty years of organizing and forming a union called the United Farm Workers(UFW) in California. He urged the government to ban the use of pesticides in the growing of grapes, demanded better working conditions, better pay for the workers not only in California, but all over the country..(Ref.7)

Science Makes Sense-Week31:Organic Chemistry, Cyclic compounds, alicyclic and aromatic.

April 4, 2016

When people visit young mothers with little babies in India, they first place a little sugar in the mouth of the baby and then give money. The baby is not interested in the money, but the little one lights up when the sugar hits the palate! Sugar, chemically, is a cyclic hydrocarbon compound.
Today we shall look at simple cyclic hydrocarbons, their general formula, nomenclature and some well-known cyclic hydrocarbons including sugars with different groups attached. We shall look at their uses and properties and briefly touch on aromatic compounds as well.
Cyclic hydrocarbons are hydrocarbons that form a ring. The simplest of cyclic hydrocarbons are cyclo-alkanes, which are saturated hydrocarbons. Let us start with the smallest ring (looking like a triangle) that will have 3 carbons and 6 hydrogen atoms called cyclo-propane with the formula C3H6. The next one in the series will be the 4-membered ring, cyclo-butane,C4H8, resembling a quadrilateral; the third one will be a 5-membered ring called cyclopentane, C5H10.(Ref.1) As one can see, the general formula resembles a straight-chain alkene and not a straight-chain alkane. Most cyclo-alkanes have similar reactivity to their corresponding alkanes.(Ref.2)
In cyclo-alkanes the carbon-carbon bond is sp3 hybridized and the ideal angle is 109.5 degrees, but in cyclo-propane and cyclo-butane the angles are 60 and 90 degrees respectively, making them unstable and reactive molecules.(Ref.1)
Sometimes these cyclic compounds might even have straight-chain hydrocarbons attached to them and then they are called generally by the term alicyclic compounds. The straight-chain hydrocarbons along with the saturated cyclic hydrocarbons are classified as aliphatic compounds(Ref.3)
Sugars are also cyclic compounds, but they are not cyclic hydrocarbons. Just like the word ‘table salt’ refers to a particular kind of salt in chemistry, the word ‘table sugar’ refers to a particular sugar in the world of chemistry. ‘Table sugar’ or sugar used at home is chemically known as sucrose and is a di-saccharide, which means two cyclic compounds, linked (through an oxygen atom) together containing four hydroxyl groups in each cyclic structure (one is 6-carbon chain and the other is a 5-carbon chain each with an oxygen instead of a carbon in its cyclic chain)instead of hydrogens. Some sugars like fructose are mono-saccharides containing the five chain cyclic poly-hydroxyl compound mentioned above and so is glucose with the same chemical formula as fructose(C6H12O6) but being the 6 carbon chain with one replaced by an O. In fact sucrose is manufactured with the starting mono-saccharides fructose and glucose. All sugars are sweet and are a store-house of energy, falling under the biological umbrella of carbohydrates.(Ref.4)
So far we have looked at examples of alicyclic compounds, but there is a vast number of cyclic compounds containing the benzene ring in them and are called aromatic compounds. Let us first look at the history and structure of benzene to understand these cyclic compounds.
Kekule, a German scientist pondered for days to figure out the structure of benzene whose chemical formula indicated six carbon and six hydrogen atoms. He kept thinking of straight-chain structures and was unable to arrive at any reasonable arrangement of the carbon and hydrogen atoms. Exhausted, he lay down to sleep and had a dream about a serpent eating its tail. Of course! Benzene was a ring structure with alternating double bonds that satisfied the chemical formula finally..(Ref.5)
We will continue the discussion of aromatic compounds, since the derivatives of benzene are vast and have great practical applications.
Activities for Middle School Teachers:
Students can once again create models of straight-chain alkanes, alkenes from carbon 1-10, 2-10 respectively. Then they can compare the structures and angles of C-C bonds with cyclo-alkanes starting of course with n=3, where ‘n’ refers to the number of carbon atoms and go up to n=10. Create a graph plotting number of carbon atoms to the angles between adjacent carbon atoms. Let students do a research project on actual angles seen with cyclo-alkanes having more than 5 carbon atoms. Are there stereo-isomers here as well?
Students can look at the chemical structure of cholesterol (Look up nuggets) and know what exactly ‘good’ and ‘bad’ cholesterol means.
Nuggets of information:
Cyclohexane is manufactured by the hydrogenation of benzene, a six carbon ring which is unsaturated. The nitration of cyclo-hexane leads to nylon products and its derivatives like balloons, ropes, etc.(Ref.1)
Sometimes, cyclic hydrocarbons are also called Naphthenes; these are the by-products of petroleum, usually cyclohexane and cyclopropane.(Ref.6)
Cholesterol, is another alicyclic compound with one of the six-membered carbon ring having an unsaturated bond. There are 3 parts to this compound: a hydroxyl group, a ring structure with 4 hydrocarbon rings and a hydrocarbon tail. The -OH or hydroxyl group is polar and soluble in water, so cholesterol is an alcohol. The 4-ring region lets us know it is a steroid hormone like estrogen or testosterone. All steroids begin with cholesterol. Since we have both the hydroxyl group and steroid part, it is called a sterol. The hydrocarbon tail is non-polar and is soluble in fats and not in water, making cholesterol not soluble in the blood stream.(Ref.7)
Brain scans reveal that sugar affects us in ways similar to drugs.(Ref.8)
Benzene is sometimes depicted as a hexagon with a circle inside it; this means that the electrons responsible for the alternating double bonds flow around like a ring of electrons.(More next time in Organic Chemistry)

Science Makes Sense- Week 30: Hydrogen, Helium, the very light gases

March 28, 2016

In the days of black and white photography, how can those who lived in the early part of the 20th century ever forget what happened on May 6th,1937? Today one can watch that video clip of the Hindenberg disaster that gripped the world then and is still quite dramatic and shocking to see now. The words of the reporter “Oh the humanity …..!” is something you cannot get out of your minds. This was a major tragedy that, if it had not occurred, would have changed the face of modern aviation completely.(Ref.1)
It was a chemistry blunder when hydrogen, a very inflammable gas was used to send the blimp with so many passengers up in the air. And it was not as if scientists did not know the easy burning of hydrogen. However, it was cheaper to use and had greater lift than Helium and was chosen since early test runs with the Hindenberg happened without any hitches.(Ref.2)
Hydrogen and Helium are both gases and are the only two elements on the first row of the Periodic Table. However, in spite of being gases, their properties could not be more different. Hydrogen,H, is the most abundant element in the universe, while Helium,He, is less than 0.0005%. H is very reactive and is hardly found as an element, whereas He is the first of the Noble inert gases and is not reactive.(Ref.3) The electronic structure gives us a hint; H is 1S1, whereas He is 1S2, which means the first s orbital is filled up and is a stable doublet.
Hydrogen is a colorless, odorless gas but is extremely reactive and forms myriads of compounds readily.
Let us delve into the differences of these two light gases.
Hydrogen is a gas and is the lightest element known. It is the only element with no neutrons and has 1 proton and 1 electron. However,it has two other isotopes, Deuterium that has a neutron and Tritium that has two neutrons. Hydrogen is not usually found in its elemental form on earth but is found as such in many planets especially Jupiter and is abundant in stars.(Ref.4)
Hydrogen has two oxidation states, +1 and -1. This makes it both an oxidizing and reducing agent. It is positively charged when reacting with halogens or oxygen and has a negative charge reacting with alkali metals.(Ref.4)
Helium, He, is also a colorless, odorless gas and has the second lowest atomic weight. Very little He is found in the earth’s atmosphere. Being such a light element, unconfined He immediately begins rising and escaping from the planet. However a lot of helium produced commercially is obtained from the ground. Some natural gas fields have enough helium mingled with the other gases to be extracted economically. Most of the helium recovered this way is thought to be formed as a result of radioactive decay of uranium and thorium found in granitoid rocks(See Activities for Middle School Teachers).(Ref.5)
Till World WarII, Helium was used in blimps, dirigibles, weather balloons or to fill balloons for parties and other festive occasions. Today it is used as a purging gas since it has the lowest melting and boiling point of any gas and is inert.(Ref.5) (A purging gas displaces other gases or liquids stored in tanks/containers.)
Since helium is an inert gas with low reactivity, high thermal conductivity and low density, it is an ideal gas to use in metallurgical processes, growing crystals in chemical vapors and manufacturing optical fibers, etc.(Ref.5)
Helium has very low atomic weight, high diffusion coefficient which means it escapes easily; hence it is used for leak detection. It is also used in breathing mixtures for deep water diving and medical procedures since it has a low viscosity and is easier to breathe under high pressure. A Helium atmosphere is good for welding processes since it does not react with the metals being welded.(Ref.5)
Hydrogen and Helium are both light gases; one electron and proton change causes such drastic differences in their properties and uses. One is present in almost everything but the other is hardly around us in the atmosphere. Yet both manage to play important roles in our lives.
Activities for Middle School Teachers:
Look at all the compounds in organic and inorganic chemistry that contain hydrogen. How many kinds of bonds are formed by a hydrogen atom? What classes of compounds in inorganic chemistry have to contain hydrogen? Are there compounds in organic chemistry that do not contain hydrogen? What is their number compared to those that do contain hydrogen?
Students can do a simple activity bringing everyday objects from home and figuring out if they contain the element hydrogen in them.
Look at the different kinds of rocks studied in geology. At least two types of rocks show the presence of helium. How are they formed in the earth? Where are they found on the earth?
Nuggets of Information:
Hydrogen, the lightest element of all, explodes at concentrations of 4-75%by volume in the presence of sunlight,flames or sparks.(Ref.4)
Despite being a stable element, hydrogen forms many bonds and exists in a wide variety of compounds. It is mostly found on earth as hydrocarbons and water.
The 3 isotopes of hydrogen show different properties because of the differing number of neutrons in the nucleus. Deuterium and its compounds are used in chemical experiments as well as in H-NMR Spectroscopy.(Ref.4)
In aqueous solutions the H+ ion is actually H3O+ or hydronium ion and this ion is extremely important in acid-base chemistry.(Ref.4)
The word ‘helium’ comes from the Greek word meaning sun (helios).(Ref.6)
The U.S. is the world’s largest supplier of helium, found in many natural gas fields.(Ref.6)
The balloon boy hoax on October 15, 2009 made people believe that a six-year old boy had floated away in a home-made helium balloon. But in reality, the boy was just hiding in his home.(Ref.6)
Since helium is less dense than air, when inhaled from a source, say, a helium balloon, it briefly changes the voice of the person to sound much higher. However, breathing too much helium could choke people due to lack of oxygen.(Ref.6)
Liquid helium is used for cooling metals in superconductivity experiments.(Ref.6)
Helium is a non-renewable source since the decay of thorium and uranium is slower than the rate at which it is being used. In 1925, the U.S. established a National Helium reserve and there was plenty of helium available. However, with more and more usage of helium as a purging gas and other uses and the selling of it to other countries, today we are at the stage that by 2021, the National Helium Reserve will be sold out.(Ref.5)


Science Makes Sense-Week 28: Chemistry and Social Justice, Air Pollution in India

March 14, 2016

I go to India in December to be with my siblings and spend most of my time in Chennai, a south-eastern city along the Bay of Bengal. Every year I notice that construction is booming with more and more multi-story structures and houses all over the city. Apart from that, vehicular traffic on the roads keeps increasing. This year I found myself struggling with a hacking cough and continuous throat irritation.
There is an urgent need to address air pollution here. It is important to understand the unique blend of pollutants present in India versus countries like the United States. As students of science one needs to have a general idea about measurement techniques as well. As social justice advocates it is imperative to look at the alarming health effects to the citizens and what measures are being taken to counteract this.
Even though the capital of India, New Delhi, is considered to have the worst Air Quality Index (Ref.1), or AQI, Chennai, seemed to be worse than new Delhi in 2015.(Ref.2)
What is AQI? Basically it is an index that lets one know how polluted or safe the air quality is in a particular country. Depending on the industries and the culture of daily life prevalent in the country, there are several different pollutants present in the air. One usually calculates its concentration for a 24 hour period in 3 -4 hour intervals. The AQI ranges from 0- 500+ and the higher the value the more polluted is the air. Several countries use a color code to indicate the levels of different pollutants ranging from safe to highly polluted/dangerous.(Ref.3) In the US, we often hear about ozone levels and PM2.5 and PM10 along with a few chemicals like sulfur dioxide etc.(PM2.5 is particulate matter less than 2.5 microns in diameter and PM10 is particulate matter less than 10 microns in diameter. A grain of sand is 50-70 microns in diameter. A micron is one millionth of a meter.)
In India, apart from the above mentioned pollutants the presence of nitrogen dioxide, ammonia,lead, benzene, nickel, carbon monoxide, arsenic levels are calculated to measure AQI.(Ref.4)
Why does India have all these extra air pollutants? As a rapidly industrializing country, there is a lot of coal production that leads to incomplete combustion forming carbon black(particulate matter,soot), carbon monoxide as well as lead, arsenic and oxides of nitrogen and sulfur.(Ref.5) Ammonia is present in decaying garbage, excreta as well as in pesticides.(Ref.6) Benzene and other such aromatic hydrocarbons are present because there is indoor air pollution especially in rural households where biomass, which is plant waste matter,(Ref.7) is burned during cooking, along with incomplete combustion products like carbon, carbon monoxide.(Ref.8) Nickel is present also in fossil fuel emissions as well as in the cement industry.(Ref.9)As you can see, India poses unique problems because of very severe indoor and outdoor pollutants.
The measurements of these pollutants is done using statistical analysis, gravimetric (where the element or compound being studied is isolated in a solid form and weighed)studies. In some cases, based on the chemical properties of the pollutants chemiluminescence, specroscopy as well as gas chromatography are some of the other tools utilized to do some quantitative analysis.(See Nuggets for more clarification of new terms.) All the measurements are done in terms of micrograms of the pollutant per cubic meter.(Ref.4)
Once the measurements are done for the 24 hour period, the range of pollutants present decides how safe or hazardous the air quality is for the day. 6 color codes are used in India; the safest is when the pollutants present is below 50 micrograms per cubic meter; satisfactory is around 50-100 micrograms per cubic meter; 101-200 micrograms per cubic meter is moderately polluted whereas 200 and higher will be classified under poor, very poor and severe conditions.(Ref.10)
The Air Quality Index determines the level of pollutants and as already pointed out, certain major cities in India constantly surpass safe levels many days of the year. People with asthma and other lung infections are particularly prone to severe attacks and the color codes advise them to stay indoors. However, even people with no specific health problems are prone to get headaches, coughs and throat irritations. As the threat level increases from moderately polluted to higher levels, more serious health issues are observed with the populace. There are respiratory diseases, problems during pregnancy and sometimes even death due to dangerous levels of air pollution.(Ref.11)
What is being done to combat these problems? In New Delhi, where the AQI is consistently one of the worst in the world,the government decided in early January of this year to have half the cars on the street, by having odd-even licence plate cars on the street on alternate days. Initially not much improvement was seen in the AQI, but with time and the additional factor that more people started using public transportation, the air quality has considerably improved. (Ref.1)
There is also the feeling that the Supreme court in India has the power to mandate certain reforms. Earlier in the 80’s the court mandated that compressed diesel should be used in the Delhi city buses and that did improve air quality for a while. The legislature now should go for a 30 percent tax on the sale of diesel vehicles, charge higher automobile registration and parking fees, and get more buses on Delhi’s roads. Then the Supreme Court could use its authority to order compliance with these recommendations. Finally, India’s national air-quality standards must be made legally binding.(Ref.12)
The Center for Science and Environment (CSE) is a public interest research and advocacy organisation in New Delhi. CSE researches into, lobbies for and communicates the vital need for development that is both sustainable and equitable. They believe in balancing the rural based life style of doing sustainable agriculture using biomass with the rapidly industrializing urban world in India. CSE brings out a lot of pamphlets and information articles to educate, promote the need for better air quality and care for the environment while rapidly developing.(Ref.13)
The fact that more and more people are aware of AQI is a start. There is even a smart phone app for AQI and most Indians love their smart phones!(Ref.14) Civic awareness can play a major part in a country where it was citizens who clamored for reform and created the Aam Aadmi Party(The Common man’s Party) in New Delhi to create positive change. In addition, India is cutting dependence on fossil fuels by looking seriously at alternative green sources like solar energy. But the pollution is still there, there are many deaths and severe illnesses reported in India because of poor air quality and so we have a long way to go.
Activities for Middle School Teachers
Why does New Delhi have such high AQI numbers? It could have something to do with the fact that it is landlocked and the smog presence is similar to Mexico City and Los Angeles. Study geographical reasons that might exacerbate or mitigate air pollutant levels. Would sea breezes help or hinder this process?
Look at a few major cities in the world to compare and contrast air pollutants. Why do they differ?
If students have smart phones, let them study AQI in a few regions all over the world for different months of the year and plot days from different months against AQI. Is there a correlation, any pattern seen?
Study all the quantitative techniques like spectroscopy, gravimetric analysis, gas chromatography and chemiluminescence and get to use/see those instruments either at the school laboratory or through you-tube videos.
Nuggets of Information:
A Yale University research team 2014 report shows that India ranked 174 out of 178 countries in air quality, somewhere close to China and Pakistan.(Ref.15)
World Health Organization says(2014 report) New Delhi’s air quality is the worst in the world!(Ref.15)
Air Pollution is the fifth largest killer in India.(Ref.15)
The Taj Mahal is turning yellow due to coal dust, biomass burning and high fossil fuel burning in India.(Ref.16)
Chemiluminescence simply means that certain compounds emit light due to chemical reactions just like fireflies do on long summer nights.
The number of photons (quantitative measurement of light particles) emitted can help calculate the concentration of certain pollutants like nitrogen dioxide, ozone and ammonia.
Spectroscopic studies use instruments like spectrometers that are able to assay spectral data using mathematics to calculate concentrations of different compounds.
Chromatography separates several constituents in a mixture and in a gas chromatograph, one analyses the peaks, the position of the peaks and the height of the peaks to identify compounds and analyse concentrations of the compound as well.