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We all know that atoms join together to form molecules. But what joins the atoms to each other in a molecule? What is the "glue" that holds the molecule together?
To find out what joins atoms to each other in a molecule, it helps to know a little bit about atoms themselves. As you may know, an atom is made of a tiny core called a nucleus, with tiny particles called electrons traveling about the nucleus. Sometimes when atoms come together, two electrons will start to travel about the nuclei of both atoms. The two atoms then share the pair of electrons. With the pair of electrons happily traveling about both atoms, the two atoms are bound together. This is called a covalent bond. When we draw pictures of molecules we draw a single line between two atoms, and this line represents a pair of electrons. For example, a chlorine molecule, made from two chlorine atoms, is drawn like this:
Sometimes two atoms share more than one pair of electrons. If they share two pairs, we draw two lines. For example, in this molecule of ethylene, the two carbon atoms are sharing two pairs of electrons:
Note that each carbon atom also shares pairs of electrons with two hydrogen atoms. Sometimes even three pairs of electrons are shared. In this hydrogen cyanide molecule, the carbon atom (C) and the nitrogen atom (N) share three pairs of electrons:
The type of covalent bonding that joins a few atoms together to make the small molecules on this page can join thousands of atoms together to form macromolecules.
This has been a very simple explanation of covalent bonding, and if you're interested in knowing more about covalent bonding, please go visit the websites listed below.
For more information, at other Web sites...
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Bonding and
Isomerism — an in-depth lesson on chemical bonding from the ChemTeam at Diamond Bar High
School.
Chemicial Synthesis, Structure and Bonding — biographical sketches of some scientists who shaped our understanding of chemical bonding, part of Chemical Achievers from the Chemical Heritage Foundation.
Lewis Dot Structures — a tutorial from the University of Waterloo, Waterloo, Ontario.