is a covalent chemical bond? In a simple wooden model, two balls
representing atoms are connected by a stick symbolizing the bond.
What is the "stick" that holds the atoms together in a real molecule?
How does a pair of electrons keep two atoms from flying apart? Just
as important, how many bonds can a particular type of atom form
with other atoms, and in what directions in space? Only when we
can answer these questions can we understand how molecules are constructed
and how they behave.
As we saw with the H2 molecule in Chapter
2, a bond between two atoms is formed by the sharing of a pair of
electrons between the atoms. This is illustrated on the right. The
bonding pair of electrons spends most of its time between the two
atomic nuclei, thereby screening the positive charges from one another
and enabling the nuclei to come closer together than if the bonding
electrons were absent. The negative charge on the electron pair
attracts both nuclei and holds them together in a bond.