A molecule is the smallest part
of a substance called a compound that still is that substance. For example,
a molecule of water is the smallest bit of water that still is water. A molecule
of a substance cannot be seen by the naked eye - a drop of water is made up
of many, many molecules of water.
Molecules are composed of atoms
joined together chemically. Molecules do not have an electrical charge.
Scientists believe that molecules
are always moving. They can be solids, liquids or gases. Molecules move the
most and are the furthest apart when they are gases. Molecules are closest together
and move the most slowly when they are solids. Molecules that are liquids movement
is between those of gases and those of solids.
A formula tells what elements
make up a molecule. For example, a molecule of water is made up of two hydrogen
atoms and one oxygen atom. The formula for a molecule of water is H2O.
Molecules come in different sizes
and molecular weights. Their atoms can be arranged in different ways. Molecules
in substances can be split up in chemical reactions to form other molecules.
They can also recombine into larger molecules or be broken down into smaller
molecules,
