Archive for April, 2016

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)