Nutrition Science and Everyday Application - beta v 0.1

AN INTRODUCTION TO MOLECULES 23
Figure 1.3. Diagram of a lithium atom, showing the placement of protons, neutrons, and
electrons. Protons and neutrons are found in the nucleus (center) of the atom. Electrons are found
outside the nucleus.
MOLECULES AND COVALENT BONDING
Atoms combine to form a larger and more complex entity called a molecule. Molecules are
composed of two or more atoms held together by chemical bonds.
The electrons of an atom contain energy. This energy is stored within the charge and
movement of electrons and the bonds that atoms make with one another. However, this
energy is not always stable, depending on the number of electrons within an atom. Atoms
are more stable when their electrons orbit in pairs. An atom with an odd number of
electrons must have an unpaired electron. In most cases, these unpaired electrons are
used to create chemical bonds. A chemical bond is the attractive force between atoms and
contains energy. By bonding, electrons find pairs, and atoms become part of a molecule.
The most stable situation for an atom is to have its outer shell completely filled with
electrons. It is not easy to explain why this is true, but it’s a rule of thumb that predicts
how atoms will react with each other. The first electron shell of an atom is considered
full (or stable) when it contains two electrons, and the second and third shells are full
(stable) with eight electrons. Atoms tend to bond to other atoms in such a way that both
atoms have filled outer shells as a result of the interaction. While some elements may be