CHAPTER
148 ❯
Bonding
IN THIS CHAPTER
Summary: The difference between elements and compounds was discussed
in the Basics chapter, and chemical reactions were discussed in the Reactions
and Periodicity chapter. But what are the forces holding together a compound?
What is the difference in bonding between table salt and sugar?
What do these compounds look like in three-dimensional space?
Compounds have a certain fixed proportion of elements. The periodic
table often can be used to predict the type of bonding that might exist
between elements. The following general guidelines apply:
metal + nonmetal → ionic bonds
nonmetal + nonmetal → covalent bonds
metal + metal → metallic bonding
We will discuss the first two types of bonding, ionic and covalent, in some depth.
Metallic bonding is a topic that is very rarely encountered on the AP exam. Suffice
it to say that metallic bonding is a bonding situation between metals in which the
valence electrons are donated to a vast electron pool (sometimes called a “sea of
electrons”), so that the valence electrons are free to move throughout the entire
metallic solid.
The basic concept that drives bonding is related to the stability of the noble
gas family (the group VIIIA or group 18 elements). Their extreme stability (lower
energy state) is due to the fact that they have a filled valence shell, a full complement
of eight valence electrons. (Helium is an exception. Its valence shell, the 1s, is filled
with two electrons.) This is called the octet rule. During chemical reactions, atoms lose,
gain, or share electrons in order to achieve a filled valence shell, to complete their
octet. By completing their valence shell in this fashion, they become isoelectronic,
having the same number and arrangement of electrons, as the closest noble gas.11
KEY IDEA