Chemistry, Third edition

Bonding Between Atoms

Objectives

Explains why elements react

Describes the extreme types of bonding between atoms

Links the properties of compounds to the bonding within those compounds

Extends the description of bonding in compounds to include ‘intermediate’

bonding types

Why atoms combine

You have already seen that atoms of different elements react together to form

compounds. The forces that hold these atoms together in compounds are called

chemical bonds. In order to understand the nature of these bonds, perhaps we

should first ask the question: Why do atoms bother to combine in the first place?

Noble gases

Clues to the answer to this question may be found by considering a group of

elements known as the noble(orinert) gases: helium (He), neon (Ne), argon (Ar),

krypton (Kr), xenon (Xe) and radon (Rn). Inert means ‘inactive’ or ‘idle’, and

describes the chemical reactivity of these elements. They are unreactive and for this

reason are said to be chemically stable. He, Ne and Ar do not react with any other

elements, whereas Kr and Xe react only with highly reactive fluorine. What is it that

makes them so unwilling to react?

The electronic structures of the atoms of these elements are listed in Table 4.1.

With the exception of helium, the atoms have eight (or ns^2 np^6 , where nis a whole

number greater than one) electrons in the outer shells of their atoms. The arrange-

ment is called a stable octetof electrons. There seems to be a stability associated

with this arrangement, and with the unique electron configuration of helium, which

makes the gases unreactive.

Lewis symbols

In 1916, Kossel and Lewis proposed that atoms of elements react with each other in

order to achieve the stable electron arrangements of the noble gases. In order to

4.1

Contents

4.1Why atoms combine 46

4.2Ionic bonding 47

4.3Covalent bonding 52

4.4Coordinate bonding 56

4.5Ionic and covalent
compounds – two
extremes 57

4.6Resonance structures 60

4.6Revision questions 62

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