By Robert Hazen, Ph.D., George Mason University
More than 90 percent of all the known compounds in chemistry are carbon-based compounds. And, by far, organic chemistry is the largest subject in chemistry today. The total production of organic chemistry is just vast. It includes all the plastics, all the paints, the glues, the drugs, the cosmetics that are used, and also the fuels—gasoline, kerosene, natural gas, heating oil.
Different Types of Bonding in Chemistry
So let’s begin by thinking about the strategy that carbon adopts in its quest for chemical stability. Chemical bonds reflect a tendency of atoms to try to find a filled shell of electrons. That is, either two electrons, or eight more, which gives you ten electrons, or eight more than that, which gives you 18 electrons, and so forth. Those are the filled shells, which are particularly stable.
So, there is ionic bonding, in which one atom gives up an electron and becomes a positive ion. Another atom takes up that electron and becomes a negative ion. And the ions bond together through electrostatic forces. And there is metallic bonding, where all the atoms in a collection give up some electrons, form a negative sea of electrons, and then there are positive charges interspersed, and that holds the metal together.
And finally, covalent bonding, in which just a few atoms together share their electrons so that every atom sees that magic number. Each of these strategies—that is to accept electrons, to share electrons, to give away electrons—can result in lower energy.
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When Carbon and Oxygen Bond
Let’s take a look at oxygen, the element eight. It needs two extra electrons, so it often forms a double bond with carbon, sharing four electrons in total. You can think of the letter C next to the letter O with two lines drawn between them. And that double line, that equal sign, represents two pairs of electrons that are shared.
So, the oxygen’s fully satisfied; it had 8 electrons, to begin with, it sees two more, and now it has ten. The carbon has two of its four electrons satisfied. So, for example, it can bond to two more hydrogens. And in that case, you get the carbon-based compound called formaldehyde, CH2O.
Carbon has three neighbors. The oxygen shares two electrons, each of the hydrogens shares one. There are other larger aldehydes that just form by replacing the hydrogen with the CH3 group. Now in carbon dioxide, CO2, you have a carbon with two neighboring oxygens.
Each of those oxygens shares two pairs of electrons. Oxygen atoms can also form parts of rings; they can form parts of chains. In fact, anything that satisfies the two electrons that oxygen needs and the four that carbon needs is possible.
Learn more about carbon’s unparalleled ability to form covalent bonds.
Alcohols As Examples of Carbon-based Compounds
Now, let’s look at another important group of atoms that involves oxygen, and that’s the OH group. If you think about oxygen bound to one hydrogen, then hydrogen is fully satisfied. It now sees two electrons. The oxygen now has nine electrons; it wants one more. So the OH group can form a single bond and can share a single pair of electrons with carbon.
So, if you start with methane, CH4, take away one hydrogen, which has a single bond, and replace it with an OH, which has a single bond, and you form methanol CH3OH, that’s the simplest of the alcohol. You can form larger and larger alcohols, once again, just by replacing another one of the hydrogens with CH3.
For example, the two-carbon alcohol is ethanol, C2H5OH, and that’s the common alcohol of alcoholic beverages and one of the most popular carbon-based compounds. You can replace it with methane, or you can replace one hydrogen with an OH group, two more hydrogens, and then you have the compound formic acid, C, H, O with two bonds, and OH. Formic acid, [CHO(OH)], is the simplest of what’s called the carboxylic acids, which are absolutely vital in our own metabolic process.
Learn more about the properties of materials.
Interaction of Carbon-based Compounds with Other Elements
Let’s see how it goes with nitrogen, that’s element seven; it needs three extra electrons, and so here there are many different strategies. Nitrogen can form a triple bond with carbon. It can also form an NH group and form a double bond with carbon. Or you can have an NH2 group and form a single bond with carbon. Those are the amines of amino acids.
Now, going to the periodic table, there are also some other elements. For example, in life, phosphorus, which lies immediately below nitrogen, and sulfur, which lies immediately below oxygen, are also very important elements. Indeed, sulfur acts very much like oxygen, with one important difference. Sulfur compounds have a notoriously horrible smell.
Phosphorus lies right below nitrogen, so phosphorus has a lot of similarities with nitrogen also in organic chemistry. And here again, the rules of the game are simple. Carbon wants four extra electrons; hydrogen wants one extra electron; oxygen and sulfur want two extra electrons; nitrogen, phosphorous want three extra electrons. And so any carbon-based compound you can imagine drawing that fills those criteria, that satisfies those needs, is possible in organic chemistry.
Common Questions about the Importance of Organic Chemistry and Carbon-based Compounds
Carbon can sometimes form a double bond with oxygen when they meet. In that instance, carbon can also bond with two more hydrogens to form a new carbon-based compound called formaldehyde. Formaldehyde’s chemical formula is CH2O.
To form methanol (a carbon-based compound), a methane molecule and an OH group are needed. Methane, CH4, takes away one of its hydrogen atoms and replaces it with the OH group to form a chemical formula CH3OH.
Carbon can bond to a large number of elements in the periodic table to form carbon-based compounds. For example, carbon, in combination with nitrogen and hydrogen, forms a compound called amine. Amines are used in the formation of amino acids.
