Lesson 10, Topic 2
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# Electrovalent Bonding (Ionic)

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The main principle of this type of bonding is donor/acceptor principle.

Electrovalent bonding is the complete transfer of electrons from the outermost shell of a metal to the outer-most shell of non-metal.

The metals donate electrons while non-metals accept. After combination, both the metal and non-metal will form a stable structure i.e attain the octet or duplet structure of rare gases.

The metals being positively charged while the non-metals negatively charged.

Example

### Formation of sodium chloride (Na+cl–)

Equation for the reaction

$$\scriptsize Na \: \rightarrow \: Na^+ \:- \: e^-$$ ………….(i)

$$\scriptsize Cl \: \rightarrow \: Cl^- \: + \: e^-$$ ………….(ii)

Add equation (i) and (ii) together

The e cancel out

$$\scriptsize Na \: + Cl \: \rightarrow \; Na^+ Cl^-$$

Diagrammatic Representation

### Structure of Sodium Chloride

Sodium chloride exists as face-central cubic crystals composed of cations Na+ and anions Cl arranged as shown in the figure below.

A close look at the figure shows that the number of anions (Cl) surrounding a cation (Na+) is six, and also the number of cations surrounding a single anion is six i.e the co-ordination number of each of Na+ or Cl is six. Hence, the opposite ions exist in a simple ratio of 6:6 or 1:1.

### Formation of Magnesium Oxide (Mg2+O2-)

Equation for the Reaction

$$\scriptsize Mg \: \rightarrow \: Mg^{2+} \: – \: 2e^-$$ ………….(i)

$$\scriptsize O \: \rightarrow \; O^{2-} \: + \: 2e^-$$ ………….(ii)

The 2e cancels out

$$\scriptsize Mg \: + \: O \; \rightarrow \: Mg^{2+} O^{2-}$$

Diagrammatic Representation

### Formation of Calcium Fluoride (Ca2+F–)

Equation for the Reaction

Ca $$\scriptsize \rightarrow$$  Ca2+ – 2e ………… equation (i)

2F $$\scriptsize \rightarrow$$ 2F + 2e ………… equation (ii)

The 2e cancels out

Ca + 2F $$\scriptsize \rightarrow$$  Ca2+ F

Diagrammatic Representation

### Characteristic properties of Electrovalent (Ionic) Compounds

1. Electrovalent compounds exist as an aggregate of positively charged ions, which are held together by strong electrostatic forces

2. They have high melting and boiling points due to strong electrostatic forces which hold the ions together.

3. They are soluble in water or polar solvent but insoluble in a non-polar solvent like – benzene, ether, etc.

4. They are electrolytes or they conduct electricity in solution or molten form.

5. They are solids that do not vaporise easily.

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