Chemistry, Third edition

IONIC BONDING 49

Example 4.1

Magnesium reacts with fluorine to form magnesium fluoride.

Write an equation to describe the bonding using Lewis symbols.

Answer

The bonding in the compound can be shown by writing an equation using Lewis

symbols, as follows:

Comment

Magnesium needs to lose two electrons to attain the stable electronic configuration

of neon, so two fluorine atoms accept one electron each to also gain the same

electron arrangement as neon. Magnesium ions (10 electrons, 12 protons) with a

charge of 2+ are formed, while fluorine forms Fions. Magnesium fluoride is an

ionic compound in which the Mg2+ions and Fions are in a ratio of 1:2.

The best equation that can be written for this reaction is therefore

Mg(s) + F 2 (g)Mg2+, 2F(s)

Reaction of potassium with chlorine

The equations using Lewis symbols provide us with more information than the usual

equations for chemical reactions. The reaction of potassium metal with chlorine gas is

shown in Fig. 4.1.

(i)Write an equation, using Lewis symbols, that shows the changes in electronic structure

that occur when potassium atoms react with chlorine atoms.

(ii)Write the balanced equation for the reaction of potassium with chlorine gas (Cl 2 ).

Exercise 4B

Fig. 4.1The reaction of

potassium metal with chlorine

gas.

Writing equations for the formation of ionic compounds using

Lewis symbols

Write equations for the formation of the following compounds, using Lewis symbols. Use
Table 3.3 for electronic arrangements:

(i) magnesium oxide (MgO) from Mg and O atoms

(ii) calcium fluoride (CaF 2 ) from Ca and F atoms

(iii)aluminium chloride (AlCl 3 ) from Al and Cl atoms

(iv)lithium oxide (Li 2 O) from Li and O atoms

(v) aluminium oxide (Al 2 O 3 ) from Al and O atoms.

Exercise 4C