Mike Ewart, age 9, of Arlington Heights, I11., for his question:

WHAT IS A MOLECULE?

A molecule is one of the basic units of matter. In fact, it is the smallest particle into which a substance can be divided and still have the properties or characteristics of the original substance.

If a substance were divided further than a single molecule, only atoms or individual particles of chemical elements would remain.

Molecules are made up of atoms held together in certain patterns. Every atom is made up of a positively charged central core or nucleus, surrounded by negatively charged electrons. In a molecule, there are an equal number of positive and negative charges.

Almost all gases, most liquids and many solids are made up of molecules.