Greg Lubianecki, age 14, of Beamsville, Ontario, Canada, for his question:
WHAT IS A MOLECULE?
Molecular biology is the study of the structure and function of the large molecules essential to life. Among these molecules are proteins and nucleic acids. Proteins speed up chemical reactions that supply the energy for living cells while nucleic acids carry the information or genetic code necessary for the development of all living cells.
A molecule is one of the basic units of matter. It is the smallest particle into which a substance can be divided and still have characteristics or properties of the original substance.
Molecules are made up of atoms held together in certain patterns. Every atom consists of a positive charged central core called the nucleus which is surrounded by negatively charged electrons. In a molecule, there are an equal number of positive and negative charges.
Chemical formulas are used by scientists to show the makeup of molecules.
Almost all gases, most common liquids and many solids consists of molecules.
Molecules are held together in a group by forces called Van der Waals forces. These forces are usually weaker than those that hold the molecule itself together. The force between molecules depends on how far apart they are. When two molecules are widely separated, they attract each other. When they come very close together, they repel or push apart each other.
In a solid, the molecules are arranged so that the forces which attract and repel are balanced. The molecules vibrate about these positions of balance, but they do not move to different parts of the solid. As the temeerature of a solid is raised, the molecules vibrate more strongly.
When the Van der Waals forces can no longer hold the molecules in place, the solid melts and becomes a liquid.
In a liquid, the molecules move about easily but they still have some force on one another. These forces are strong enough to form a film like surface on a liquid and prevent it from flying apart.
In a gas, the molecules move about so fast that the attractive forces have little effect on them.
When two molecules in a gas collide with each other, the repelling force sends them apart again. Therefore, gas molecules fill a container completely because they move freely through all the space available.
Most substances can be changed into solids, liquids or gases by either raising or lowering their temperatures.