Chemistry, Third edition

IONIC BONDING 47

obtain these stable arrangements, atoms may gain, lose or share electrons. These

processes are generally represented by using Lewis symbols– an atom of an element

is represented by the symbol for that element and the electrons in the outer shellof

the atom are shown as dots, small circles or crosses. For example, the Lewis symbol

for the sodium atom is

Na

The symbol for sodium is Na and the electronic structure of the sodium atom is

2.8.1, so there is oneelectron in the last electron shell which we represent by one dot

(or cross – the choice is yours!).

Ionic bonding

When an atom of sodium reacts with an atom of chlorine, sodium chloride is

formed. The Lewis symbols for sodium and chlorine are

Although the complete electron arrangements of each atom are written underneath

each Lewis symbol, only the outer electronsare shown by dots and crosses because

they are the only ones that take part in bonding.

When a sodium atom reacts with a chlorine atom, the sodium atom loses one

electron to chlorine (to obtain the stable electron arrangement of neon), while the

chlorine atom, in gaining an extra electron, attains the stable electron arrangement

of argon. This can be represented in an equation:

Before the reaction the neutral sodium atom had 11 electron and 11 protons.

After giving an electron to chlorine, the sodium atom has 10 electrons and 11 pro-

tons, so it is not electrically neutral – it carries an overall positive charge equal to the

charge of one proton (+1). The new species is written Na+and is called a sodium ion

4.2

Table 4.1Electronic structures of the noble gases*

Inert Electronic structure Electronic structure
gas (Bohr model) (s,p,d,f notation)

He 2 1s^2
Ne 2.8 [He] 2s^2 2p^6
Ar 2.8.8 [Ne] 3s^2 3p^6
Kr 2.8.18.8 [Ar] 3d^10 4s^2 4p^6
Xe 2.8.18.18.8 [Kr] 4d^10 5s^2 5p^6
Rn 2.8.18.32.18.8 [Xe] 4f^14 5d^10 6s^2 6p^6

• To save space, the convention [noble gas] is used and refers to the
  electronic configuration of that gas. So, for example, [He] replaces 1s^2.

Lewis symbols

Write Lewis symbols (using

dots or crosses) for the

following neutral atoms.

The number of electrons in

each atom is shown in

brackets:

(i) F (9)

(ii) K (19)

(iii) Be (4)

(iv) S (16)

(v) P (15)

(vi) Ca (20)

(vii) C (6)

(viii)Al (13)

(ix) Ar (18)

(x) H (1).

Exercise 4A

2.8.1 2.8.7

2.8.1 2.8.7 2.8 2.8.8