Archive for October, 2015

Science Makes Sense, Week 10: Glass, silicon, sandy beaches, fiber optics, piezoelectricity

October 25, 2015

William the Franciscan Friar who has come to investigate a murder in the monastery, is busy getting his glass lenses ready to help him with his failing eyesight.  Humberto Eco, in his classic  “The Name of the Rose” explains with great detail about life in the 14th century where he imagines the origins of using convex glass circles to create early eye glasses. (Ref.1)

Of course glass was discovered long before the 14th century.  During 1500  BC, the first creations with glass is credited in ancient Mesopotamia, modern-day Syria.  When lightning struck sand, a brittle shiny object called obsidian was formed.  People in and around Mesopotamia shaped it as knives and sharp objects for hunting.  Glass making was tedious in those days using clay pots and long hours working with sand.  The invention of a glass blower in 30 BC changed glass production considerably allowing different shapes and forms to be created now.(Ref.2).  However, the first recorded uses of glass-like material like obsidian from volcanic areas and fulgurites (lightning striking sand) is from 7500 BC.(Ref.2)

What is glass?  Since it is created from sand which is plentiful in beaches, the main element is Silicon, Si in the form of compounds called silicate SiO44- (Ref.3).  Both Si and O are the two most abundant elements on earth.  Sand contains quartz, made up of an orderly arrangement of SiO44-  anions in a tetrahedral shape combining with other Si and O ions to have the general formula SiO2, silica and is crystalline.  Glass has the same formula, but it is amorphous and the arrangement of the anions is a short range.  The process of creating glass sometimes involves adding sodium carbonate Na2CO3 to sand and heating it to a high enough temperature and cooling it rapidly.(Ref.4) 

Glass manufacture needs three components: the former, flux and stabilizer.  The former is silica or SiO2, and alone it needs very high temperatures to melt and therefore a flux e.g., oxides of alkali metals like Na2O (soda/sodium oxide) or K2O (potash/ potassium oxide) or Li2O (Lithia/ lithium oxide) is added.  Even though now the melting point temperature is lowered, the resulting glass may be water-soluble and of low durability.  A stabilizer like CaO or BaO or MgO or PbO,( oxides of calcium, barium magnesium or lead; also called lime, baria, magnesia, litharge respectively) is also added. Common glass (for windows, jars, bottles, bulbs) contain SiO2 as former, Na2O  as flux and CaO as stabilizer.(Ref.3)  As shown in the above paragraph, sometimes Na2CO3  is used as a flux.

Glass is neither a solid nor a liquid, since the arrangement of the anions and cations are almost like a liquid but it has an appearance of a solid!  Molecular physics and thermodynamics (behavior under different temperatures) are still not clear but here are some observations:

Many solids have a crystalline structure on a microscopic scale just like Na+Cl.  The ions/molecules/atoms are arranged in a regular lattice and when the solid is heated, they vibrate until the melting point and the crystal structure breaks down. The ions/molecules/atoms flow and the solid to liquid state is a sharp transition, which explains the fixed melting point for so many solids.  This is called a first order phase transition.  The density also changes distinctly.

Let us look at the reverse process; from liquid back to the solid state.  As it cools, the viscosity (also called resistance to flow) increases, which is understandable since the ions/molecules/atoms are moving closer together.  However, this increase in the viscosity could prevent crystallization.  And it could keep cooling below the freezing point called supercooling, and may never crystallize.  The viscosity keeps rising and forms a thick syrup and finally an amorphous solid.  The molecules will have a disorderly arrangement, almost glass-like?

Therefore, glass could be considered a super-cooled liquid with no first order phase transition, but a second order phase transition; between super-cooled liquid state and the glass state, not as dramatic as the liquid to crystalline solid state.  The temperature at which this glass transition occurs depends on how slowly it is cooled.

So to summarize we have three types of molecular arrangements:

  1. Crystalline solids- ions/molecules/atoms are ordered in a regular lattice.
  2. Fluids- ions/molecules/atoms disordered and not rigidly bound.
  3. Glasses- ions/molecules/atoms disordered but rigidly bound. (Ref.5)

The jury is still out on the exact definition of glass!


Activities for Middle School Teachers:

Make glassy material using some sugar syrup; also make crystalline candy with sugar syrup and study the difference in the procedure.

Silicon is present in many semi-precious stones including quartz; list the elements that cause different colors/ semi precious stones.(Ref.6)

Students can study architectural wonders in the world constructed with glass: Louvre in Paris France and La Estancia Glass Chapel in Cuernavaca, Mexico are examples.(Ref.7)

Study the different civilizations like the Mayas and in Mesopotamia and look at the role of obsidian, glass during those periods. (Refs.8,9)

Nuggets of information:

In 1664, an Englishman, Mr.Ravenscroft added small amounts of lead oxide (PbO) during the glass making process to create brilliant glass.  This led to the creation of crystal bowls and goblets.  Different grades of glassware can be created by adding different oxides:

  1. When boron oxide is added, laboratory glassware is produced that withstands high temperature.
  2. When aluminium oxide is added the glass withstands even higher temperature to keep on stove tops.
  3. High content (almost 100%) silica glass, resistant to thermal shock and chemical attack is used to make spacecraft windows, fiber optics. (Ref.3)

Fiber optics or optical wave grids are today’s communication technology that has replaced the humble copper wire.  A single strand of glass fiber, coated with a protective plastic resembles a human hair.  The glass fiber has an inner core of ultra-pure fused SiO2 coated with another SiO2 glass to act as a light reflective barrier.  Lasers are used to convert electrical impulses and sound waves to pulses of light that travel through the inner core.  1lb of glass fiber transmits the information that would formerly require 200 tons of copper wire!  These fiber optic cables criss-cross our entire earth. (Ref.3)

Cooks who create desserts and work with sugar probably know how to create glassy shards of brittle concoctions using the super-cooled process with sugar syrup, a liquid.  This same sugar syrup can be used to make crystalline candy.

In old churches, the glass is found to be thicker at the bottom of the window and people thought glass must be a liquid and flowed from top to bottom over the years.  Actually this is not true.  In Medieval times, panes of glass were often made by the blown glass method.  A lump of molten glass was rolled, blown, expanded and flattened.  Finally it was spun into a disk, which made it thicker at the edges.  When installed, the thicker side was placed at the bottom side of a window-pane. (Ref.4)

Si, like C, (being in the same Group in the Periodic Table) forms a lot of different covalent bonds with O.  Apart from quartz, talc, there are different kinds of naturally occurring asbestos that contain silicates. (Ref.4)

One of the most interesting properties of quartz is piezoelectricity, which means that when you apply pressure to a crystal of quartz, the orderly arrangement of atoms/molecules/ions is disturbed and the crystals conduct electricity.  The opposite is also true; when you apply electricity to quartz crystal, there is a shift in the position of the atoms/molecules/ions. These principles are used in a quartz watch that keeps perfect time, as well as in voice-recognition software that we use frequently. (Ref.10)

Glass containers are considered the best for storing spices and other foods.  Glass, especially clear glass in a dark cupboard or dark-colored glass, stores herbs well and does not impart any odor to the food, like plastic.

Today, most supermarkets sell liquids in plastic or paper coated with plastic containers that were previously sold in glass containers. The one place where glass use continues is in the making of all kinds of mirrors. (Ref.11) and in the manufacture of LED (light emitting diodes) lighting.(Ref. 12)


1. Eco, Humberto, The Name of the Rose, (Bompiani, 1980, English,1983)













Science Makes Sense, Week 9: Common Salt, Sodium Chloride, ionic bonds,crystallography, La Gabelle and Dandi March.

October 18, 2015

Pliny the Elder, a Roman statesman and scholar (first century) is supposed to have come up with the famous saying Cum grano salis or more accurately Addito salis grano (Ref.1) which means ‘with the addition of a grain of salt’ questioning a statement’s veracity. It is possible that expressions with salt have been there  even before the time of the Bible. In the Thirukural , a book of 1330 couplet verses of 4 and 3 words in the Tamil language, (Time period:two hundred years BC to 8th century?), there is a reference to salt almost at the end!  At the tip of India, in a city called Kanyakumari where the Bay of Bengal meets the Indian Ocean and the Arabian Sea, there is a splendid statue of Thiruvalluvar, who is credited with the poetry of Thirukural. (See third picture)

Common salt or table salt has the formula NaCl in Chemistry, and it is called sodium chloride.


IMG_2358Let us look at the structure of sodium chloride. We have already looked at covalent bonds where there is sharing of electrons, and we have seen hydrogen bonds that are weak bonds between oxygen and hydrogen in compounds like water. Now we will look at a third kind of bond here. Inorganic compounds form bonds in a different manner than organic compounds where electrons are shared. Inorganic compounds form ionic bonds, which involves a transfer of electrons from one element to another element or group of elements. Many of the elements in the Periodic Table can form these ionic bonds. Today we will look at the simplest ionic bond involving two elements : sodium and chlorine forming the compound sodium chloride. Such compounds are called binary compounds.

When a sodium atom reacts with a chlorine atom, the sodium atom gives up one electron and becomes a positive ion(cation),the sodium ion,Na+. (All atoms are electrically neutral)  The chorine atom accepts the electron and becomes a negative ion(anion), the chloride ion,Cl

The bond is actually the attraction of oppositely charged particles :Na+Cl, so technically it is not a bond like the covalent bond  where two shared electrons constitute a bond. Since these are charged particles, a solution of sodium chloride or molten sodium chloride will conduct electricity. In fact, all ionic compounds in the molten state or in a solution will be conductors of electricity.Other properties of ionic compounds include high boiling and melting points, solubility in water (for some ionic compounds) and defined crystal shapes.(Ref. 2)

What is a crystal? It is a definite arrangement of atoms, molecules or ions in a periodic pattern in three dimension. (Ref.3) Let us look at a crystal of sodium chloride or more accurately Na+Cl–   

Every sodium ion is surrounded by 6 chloride ions and each of the chloride ions are surrounded by six sodium ions as shown in the second picture. The crystal structure of sodium chloride is cubic.The larger green circles in the second picture are chloride ions and the smaller blue circles are sodium ions. Why are the sizes different?

First let us look at the position of Na in the Periodic Table. It is the 11th element in the Periodic Table. and then it loses an electron to become a cation,Na+.  It loses the outer electron in the second shell and also has one more proton than electron and the attraction to the nucleus is more and hence becomes much smaller.  Meanwhile  the chloride ion,Cl.has 18 electrons and only 17 protons, nuclear attraction to each electron is decreased and allows the Cl atom to expand as it forms the Cl   This makes the Cl  to be considerably larger than a Na+.(Ref.4)

Many ionic compounds form crystals and the order and arrangement of the atoms can be studied by crystallography. Using X-rays, or neutrons , a single crystal of any ionic compound is studied; a pattern of spots are seen and using mathematical models, the arrangements of the atoms/ molecules/ ions can be deduced.(Ref.5)  Just as visible light is part of the electromagnetic spectrum, X- rays with much shorter wavelength are part of this same spectrum. (Ref.6)IMG_1795

This ionic compound, sodium chloride, has played a critical role in the history of the world.Before industrialization and definitely before refrigeration,salt was a much-needed commodity for food preservation. We will talk about the spice trade where wars were fought over the pepper trade, but everyone forgets the importance of salt, which is fundamental for living and caused upheavals in many countries.

When the British ruled India for over 200 years, they imposed a salt tax and made it very difficult for poor Indians to get their daily intake of salt In fact, there is evidence that it resulted in the death of many people due to a  lack of salt in their systems. Mohandas K Gandhi, the freedom fighter, who used non-violent methods to achieve India’s independence refused to buy salt from the British. He started a long march, called the Dandi March to walk to the seashore on the west coast of India to evaporate salt from the sea and use it instead.(Ref. 7)

In France, from the 14th through the 18th century, high salt taxes called la gabelle  were levied and caused a lot of anger and resentment among the people.(Ref.8) Even during the Civil War in the United States in the latter part of the 19th century, the South’s supply of salt was destroyed by the Union forces; tactics used to cripple the South’s effectiveness in the battlefield.(Ref.9)

No wonder so many sayings throughout the world mention salt, this small ionic compound called sodium chloride.

Activities for Middle School Teachers:

Students should have a discussion about sayings with salt in their cultures. It would be interesting to see how vital a role salt has played in our lives for so long.

Let students sharpen their idioms in English by thinking of all the sayings that are common using salt; eg, “rubbing salt to one’s wounds”, ” worth your weight in salt” etc.

Let students grow crystals of salt in the laboratory. let them examine the little crystals called seed crystals that may be found at the bottom of the beakers using magnifying glasses, what are their shapes?

Confluence of geometry and atomic arrangement: The Na+Cl–  crystal has perfect symmetry among all the 14 Bravais crystal lattice structures. (Students need to understand the different types of symmetry, mirror image symmetry, rotational symmetry etc.)(Ref.10) Here a=b=c and the angles are all equal to 900. Students could construct the 14 possible arrangement of atoms/molecules/ ions among the various crystal structures.

How did people look for salt long ago besides going to the salt water areas? Let students search for salt- water lakes all over the world as a geography project.

Students can read the following books about salt:”Men of Salt” by Michael Benanav,”Salt” by Neil Morris and “Salt” by Mark Kurlansky.(Refs.11,12,13) The third book is considered a must for anyone interesting in cooking/food.

Nuggets of Information:

Crystals of sodium chloride are also called halite crystals.

Why do some elements like to give up electrons and others prefer accepting them? Look at the Periodic Table and you will notice that elements on the left side of the Periodic Table in the first two groups and the Transition Elements give up electrons to attain the electronic configuration of Noble Gas elements like He, Ne, etc.that are before these elements These elements are called metals

On the other hand, Cl, Br, F as well as O, S, N etc, on the right-hand side of the Periodic Table, like to take electrons to attain the electronic configuration of the Noble Gas that follows them. These elements are called non-metals.

Even though salt, NaCl, is essential for all of us, today we are dealing with health problems because of too much salt in our foods especially processed foods like canned soups. Obesity, high blood pressure are some of the negative effects of too much salt in our diets.(Ref.14)

In Chemistry, when we use the word ‘salt’ we are not just talking about NaCl. A reaction between an acid and a base creates salt and water. There are many salts that are created this way and one of them  besides rock salt, (NaCl) can be used on the roadways to melt ice and snow during winter. This is a salt of calcium Ca, or magnesium, Mg.(Ref.15)

How does this salt melt the ice? It lowers the freezing point of ice when it mixes with the solid ice.

In Poland, there is a famous salt mine called Wieliczka where there are salt sculptures.(Ref.16)

Look at a tribute to Martin Gardner, who wrote regularly in the Scientific American; he was obsessed with symmetry and you can make a hexaflexagon! (Ref.17)


1.Knowles, Elizabeth(editor),The Oxford Dictionary of Quotations (Oxford University Press,2001)



4. Hein, Morris & Arena, Susan, Foundations of College Chemistry, (John Wiley and sons, 2007)



7. Sinha, Sarojini, A Pinch of Salt Rocks an Empire, (Children’s Book Trust, New Delhi,1985)




11. Benanav, Michael, Men of Salt,(Lyons Press, 2006)

12.Morris, Neil, Salt, (London Franklin Watts,2005)

13. Kurlansky, Mark, Salt,(Penguin Books,2003)

14. Moss, Michael, Salt, Sugar and Fat,(New York, Random House,2013)




Science Makes Sense Week 8: Chemistry and Social Justice: burning of fossil fuels, climate change, carbon dioxide,methane levels and the monarch butterfly

October 11, 2015

There are many topics I will cover under Chemistry and Social Justice, but the excessive use and  burning of fossil fuels and its consequences seem the most urgent and grave topic for us all right now.

As some of you already know, those of us who live in the United States, know that we are dependent on fossil fuels for most of our energy sources. Today you will see through chemical reactions, what happens when fossil fuels/petroleum by-products are burnt. Petroleum by-products includes all the hydrocarbons, alkanes ,plus several derivatives that we use as fuels. When methane, ethane, propane or any alkane  burns, it combines with oxygen to give carbon dioxide and water. This is an oxidation reaction we studied (Week 2).The amount of carbon dioxide and water produced varies with the alkane; the higher the number of carbon atoms, the more carbon dioxide is produced:

CxHy + aO2 –> bCO2(g) + cH2O(g) ..                      

As you can see  x=b  which means that the higher the number of carbon atoms, the greater will be the molecules of carbon dioxide emitted; let me prove it to you with some examples:

CH4    +  2 O2      →   CO+  2H2O

2C2H6   +    7O2  →   4 CO2   +   6H2O

C3H8   + 5O2        →    3 CO2   +  4H2O

2C4H10  + 13O2    →   8 CO2   +  10H2O    

The ratio of alkane to carbon dioxide is 1:1 for methane, 1:2 for ethane and by the time you get to butane, the ratio is 1:4, which proves the statement before the equations, viz., the higher the alkane the greater the molecules of carbon dioxide produced. The amount of carbon dioxide produced has been increasing more rapidly in the 20th and 21st century, and there is a direct correlation between the increase in the amount of fossil fuels burnt in this period and the rise in carbon dioxide in parts per million (ppm)(Ref.1,3)


The concentration of carbon dioxide levels has been monitored since the late fifties of the 20th century by scientists. However, air trapped in the snows of Antarctica have led to data on carbon dioxide levels for the past 160,000 years. These studies indicate that as the amount of carbon dioxide(CO2) increased, the global temperature increased as well. Now the levels of CO2 have remained fairly constant from the last Ice Age (100,000 years ago) until the Industrial Revolution which took place in the late 18th to mid 19th  century. However, a greater rise occurred in the 20th century (greater production and use of fossil fuels in developed and developing countries) and is rising even more dramatically in the 21st century where we have reached critical and dangerous levels.

How exactly does the increase in carbon dioxide lead to climate change? The CO2 rises to the atmosphere and forms an  invisible barrier or layer around the earth, almost like a glass in a greenhouse (the earth being the greenhouse) leading to the phenomenon we call ‘global warming’ or climate change.  CO2 and CH4 (methane; see next paragraph after this)  trap heat near the surface of the earth. While the sun’s radiation strikes the earth and warms it up and the warmed surface re-radiates this energy as heat, the gases absorb some of the heat which then warms the earth. (Ref.2,3) 

When considerable ice melts in the Arctic due to global warming, CH4 trapped  in the ice is released and this combines with the CO2 to add to more global warming and the vicious cycle is repeated ( Ref.4)

The warming of the earth for the last 10,000 years has been about 1 degree Centigrade (C) but since green house gases stay in the atmosphere for a very long time, in the last fifty years we have seen almost another degree rise in C! Many countries have agreed not to go beyond the critical 2 degree C rise. But if we continue at the rate at which we are using fossil fuels, doing nothing, the rise could go up by 6 degrees C!! Scientists have shown with their climate models that at a 4 degree C rise , sea levels will rise by several feet, 40% of the earth will be uninhabitable leading to over millions of displaced people and several species will get extinct.( Ref.4)

 The terrible hurricane called Katrina in New Orleans, the horrible floods along the east coast due to Hurricane Sandy, the recent severe drought in California, the resulting forest fires and the recent flooding in North Carolina, plus the rapidly melting ice layers in the Arctic and the Antarctic regions can all be attributed to climate change. This is directly as a result of our fossil fuel culture and the consequent rise in carbon dioxide production. The melting of the ice and the displacement of animals like the polar bear were vividly illustrated in the documentary, “An inconvenient truth” publicized by Vice President Al Gore.(Ref.5) All these unusual weather patterns have caused movement of people from different regions:  New Orleans is a prime example, where the poor especially were not able to come back and are permanently displaced; a case of climate exiles.

Rising sea levels have been seen all over the world and small island countries  like Vanautu are showing alarming erosion of land and displacement  of peoples.Climate exiles will become a big problem if we do not address the problem of our heavy reliance on fossil fuel (Ref. 6 )

The reason we have not done much to counteract the use of fossil fuels by switching more to solar, wind power as alternative energy sources, is not difficult to comprehend. The tobacco lobby prevented the general public from knowing the hazards of smoking, and it took years of advocacy and presentation of evidence to connect lung cancer with smoking and change laws.  We have the fossil fuel industry today that campaigns vigorously  to deny climate change linkage with fossil fuel usage. We are encouraged to buy cars and not enough money is put into public transportation.(Ref. 7) In addition, there is pseudo-science to convince the public with false claims stating that climate change has nothing to do with fossil fuels (Ref.8) Several policy makers are beholden to fossil fuel companies and are not willing to legislate change. It  is not enough if a few countries lower their emissions, convert to alternative sources of energy ( solar, wind, waste) (Ref.7); many other countries that consume a lot of energy like the United States have to join in this venture.

The situation looks bleak here and we should be worried about the future of our planet earth. However, there are little rays of hope even here: Shell has decided not to drill in the Arctic, solar panels are back on the White House, and President Obama is definitely linking our dependence on fossil fuels with global warming/ climate change. But action is needed soon : it is needed now to respect the earth and the lives of future generations here.

Activities for Middle School Teachers:

Let students understand ppm by doing a serial dilution : starting with 1ml of  any food coloring agent added to 9ml  of water in a test-tube; taking 1ml of this solution to the next test-tube adding 9ml water, repeating this 4 more times. The 6th test-tube will be 1ppm of the food coloring.

Barbara KingSolver, a well-known writer and advocate for the well-being of the earth, wrote a  book about the demise of the monarch butterfly due to climate change and excessive herbicide use. The book is called,”Flight Behavior” (Ref.9). Students could learn about what happened to the monarch butterfly because of climate change. Many students with family in Michoacan, Mexico, might have heard stories about the migration of the monarch butterfly and the dwindling of the species.

Students could learn about ways to reduce their carbon footprint and calculate how much energy  they could save per month or per year.(Ref.10,11)

All the information given earlier about the possible devastation of the earth could make students and instructors depressed and feel helpless. Encourage students to look at courageous individuals like Dr Hansen (Ref.12) who has for years presented evidence at legislative hearings and has vowed to continue to fight against our energy choices. Bill McKibben, a long-time environmentalist with a global grass-roots movement, runs an organization called (that website has more information) to keep carbon emissions at or around 350 ppm. Let students also study what other countries in the world are doing for alternative sources of energy, look at India, Iceland, Norway,Peru, for example.(Look at second image where solar powers some signs in Tampa, Florida)

Learn about climate summits that have happened and will continue to happen every year in different countries.(Ref.13)

Nuggets of information:

Food transportation  in the United States is the largest single cause of carbon dioxide emissions.(Ref.7) Locally grown food consumed locally is more nutritious and less carbon energy intensive.

This July(2015) has been the hottest year since record-keeping began.(Ref.14)

Carbon footprint is the amount of carbon (carbon dioxide) each individual uses in a year.(Ref. 10)

The first reference to greenhouse effect because of the presence of gases was made in 1858 by John Tyndall. (Ref.15)

Jet or aviation fuel used for airplanes use higher alkanes from pentane all the way to 15 carbon alkanes, so you can imagine how much carbon dioxide is given off! There are some climate scientists who refuse to go anywhere by plane to avoid adding to the carbon footprint.

Climate scientists are seriously talking about the plight of climate exiles and which countries need to take them in when survival becomes impossible due to life-changing events like hurricanes, floods etc in their own homeland. I am proud to include my brother and sister-in-law’s articles here; they have been working tirelessly on climate change and social justice.(Ref.7,16,17)



2. Hein, Morris & Arena,Susan, Foundations of College Chemistry, (John Wiley and Sons, 2007)





7. Hillman, Mayer, Fawcett, Tina & Rajan, Sudhir Chella, The Suicidal Planet ( Thomas Dunne Books, /St.Martin’s Press, 2007)


9. Kingsolver, Barbara, Flight Behavior,(Harper/Harper Collins,2012)







2 Attachments16,17.

Preview attachment Byravan and Rajan (2010) – Ethical Implications SLR.pdf

Byravan and Rajan (2010) – Ethical Implications SLR.pdf

Preview attachment Byravan and Rajan (2015)-SLR and climate exiles-a possible solution.pdf

Byravan and Rajan (2015)-SLR and climate exiles-a possible solution.pdf
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Science Makes Sense Week 7: Organic Chemistry, covalent bonds, alkenes/olefins,isomers, saturated and unsaturated fats .

October 5, 2015

I remember noticing that bananas in this country seem to ripen faster than in India. Two days ago the banana was greenish-yellow and today it is completely yellow with brown spots, why?

Most of the bananas in the United States are picked unripe and ethylene gas is passed over them to hasten the ripening process.No wonder half green and yellow bananas turn ripe so quickly. In fact, during the natural ripening of fruits, ethylene gas is given off. What is ethylene, also known as ethene? It is the first in the alkenes (also called olefins/olefines) series I will talk about today.


(Week 3 was about alkanes.) Alkenes have the general formula CnH2n and the first one in the series is C2H4 , called ethylene or ethene, (second picture above)

Notice the two bonds connecting the two carbon atoms. Let us take a few minutes to understand what the word ‘bond’ means. There are different kinds of chemical bonds; we have seen hydrogen bonding and today we will look at covalent bonding. Organic compounds exhibit covalent bonding.

That line or toothpick (Week 3) I use to indicate a bond is actually the sharing of electrons here. All chemical reactions involve transfer of electrons and all compounds in organic chemistry consists of  the sharing of electrons. Here with only C-H bonding you have the sharing of two electrons.The carbon atom has one electron that it shares with the one electron that the hydrogen atom has leading to two shared electrons;but since there is a double bond for the C-C bond, there are actually 4 electrons here. ( If it had been a single bond as in ethane, there would be the sharing of two electrons for the C-C bond.)These two shared electrons comprises the covalent bond indicated by lines (or dots for the electrons) like shown above in ethylene or ethene.

Since we are dealing with double bonds between two carbon atoms, the first in the alkene series has to have two carbon atoms.When n=3 we have  C3H6, called propene and when n=4 it is called butene,  C4H8. When there are 4 carbon atoms, for butene, you can have the double bond between the carbon 1 and 2 and create two distinct structures. First, you can have a straight chain structure and then a branched chain structure for the carbon atoms. (You need a minimum of 4 carbon atoms to do straight and branched chains of carbon atoms.

Next, the double bond can move between the second and third carbon atoms. Now, since we have a double bond, the structure cannot rotate so positions for the attachments to the second and third carbon atoms become rigid. When the methyl ( methane is CH4 ,but when one hydrogen is less it becomes methyl written as CH3) components are on the same side it is called ‘cis’ and when they are on opposite sides it is called ‘trans’. Observe propene ( only one form) and butene with 4 isomers:


Notice that the carbon atom has 4 bonds while the hydrogen atom forms only one bond. If you have a 5 carbon alkene,it  will be pentene, and you will have more isomers possible. Many of these isomers are extremely important; slight variation in structure causes immense changes in properties. Week 11 we will look at some remarkable examples of isomers and their significance in medicine, especially.

Week 3 I covered alkanes, where the carbon atom had no double bonds, today we see a double bond in each of the alkenes mentioned. Hydrocarbons like alkanes are called saturated hydrocarbons and when a double bond or bonds are present in an organic molecule, it is called unsaturated. Oils are usually unsaturated  which means they are organic molecules with double bonds while solids like butter, lard are saturated with no double bonds. In daily life we hear the words ‘saturated fats’, ‘unsaturated fats’ and now you can at least know that the chemical structure includes single or double bonds between carbon atoms.

Alkanes are vital as fuels while alkenes are the building blocks for the manufacture of plastics. Ethene, we already know is used in the artificial ripening of fruits.

Activities for Middle School Teachers: Let students construct alkenes from n=5 to say, n=10. Let students do straight chain and branched chain for the carbon atoms and also look for the different isomers.

Let students look for a relationship between number of carbon atoms and number of isomers, is that a linear relationship? ( What is a linear relationship?)

Find out if other countries ripen fruit artificially, what chemicals do they use besides ethylene/ethene? Locate these countries in a map.

Students can study how effective unsaturated fats are compared to saturated fats for a healthy diet.

Nuggets of information: diene is an organic compound with two double bonds. Butadiene is a four-carbon hydrogen compound with two double bonds. The formula is C4H6  and the carbon double bonds are in the 1, 3 position: -C=C-C=C-

Butadiene is extremely useful today; it is the starting point for the manufacturing of synthetic rubber (Week 6)

Trans fats  today are even worse for our diets than saturated fats. The adding of hydrogen to unsaturated oils leads to a solid product like margarine where the hydrogen atoms are on opposite sides of a double bond in the oil structure. ( trans position).