Shown here are four representations chemists use for a molecule of ammonia. In the colored models, nitrogen atoms are blue and hydrogen atoms are white.
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Windows to the Universe original artwork by Randy Russell.


Most things around us are made of groups of atoms bonded together into packages called molecules. The atoms in a molecule are held together because they share or exchange electrons.

Molecules are made from atoms of one or more elements. Some molecules are made of only one type of atom. For instance, two oxygen atoms bond together to form the molecule O2, the part of the air that we need to breath to survive. Other molecules are very large and complex. Protein molecules, for example, often contain hundreds of atoms.

Other well known molecules include water, which is two hydrogen atoms bonded to one oxygen atom (H2O), and carbon dioxide, which is one carbon atom bonded to two oxygen atoms (CO2).

Each molecule is so small that you would not be able to see one molecule of a substance. But when thousands of molecules are together, they might look like a glass of water, a tree in the forest, or your computer screen, depending on what types of molecules they are.

A glass of water sitting on a table might look pretty still, but the molecules of water (H2O) and glass (Si) are moving all the time. In fact, though too small to see, all molecules are always moving and they will move faster as temperature increases.

Last modified September 17, 2010 by Randy Russell.

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