Chemical Bonding

An ionic bond is a bond which is formed by the transfer of electrons from a metal atom to a non-metal atom, forming Ions having stable electronic configuration.

1. Ionic compounds have high melting and boiling points. This is because ionic compounds form giant ionic lattices (structure) consisting of cations (positive ions) and anions (negative ions) held together by strong electrostatic forces of attraction.

Ionic compounds have a giant lattice structure and a strong electrostatic force of attraction, and thus it requires a lot of energy to overcome these forces of attraction.

The melting point of Sodium Chloride is 801℃.

The melting point of Magnesium Oxide is 2852℃.

The higher melting point of Magnesium Oxide is due to stronger electrostatic forces of attraction as a result of higher or greater charges.

2. Ionic compounds do not conduct electricity in the solid state, but they conduct electricity in the molten (liquid) or aqueous state.

Ionic compound do not conduct electricity in the solid state due to the absence of mobile ions which are locked in the lattice.

In the molten or aqueous state, ions are mobile and hence can carry the charges of electricity.

3. Ionic compounds are mostly soluble in water (Potassium nitrate, Calcium nitrate, Sodium chloride)

A covalent bond is formed between atoms of non-metals by the sharing of electrons, such that each atom obtain a stable electronic configuration.

1. Low melting and boiling point as the amount of energy which is required to overcome the forces of attraction between the molecule is low because these forces are very weak, and they are known as Van der Waal's forces.

2. The compounds or molecules do not conduct electricity in any state due to the absence of free delocalised / mobile electrons.

3. The compounds or molecules are insoluble in water, but soluble in organic solvents. (petrol, thinner)

4. The compounds or molecules are volatile. (low melting / boiling point)

Substances which are covalently bonded together and having high melting point form giant molecular structures.

1. Silica (Silicon dioxide or sand)

2. Graphite

3. Diamond

Silica forms a giant molecular structure where the Silicon and Oxygen atoms are arranged in a tetrahedral manner in a vast network (infinite assembly).

Silicon dioxide has a high melting point (about 1410℃) because a large amount of energy is required to break these strong bonds.

In the structure of Silicon dioxide, each Silicon atom is covalently bonded to four oxygen atoms, while each oxygen atom is bonded to two Silicon atoms.

Silicon dioxide does not conduct electricity because it does not contain free delocalised atoms.

Allotropes are different forms of the same element, having different arrangement of atoms.

Graphite forms a giant molecular structure consisting of many strong covalent bonds. This explains why Graphite has a very high melting point (3650℃) as a large amount of energy is required to break these strong covalent bonds.

Graphite has a layer structure consisting of carbon atoms arranged in hexagonal rings. Each Carbon atom in Graphite is covalently bonded to three other Carbon atoms.

Graphite is soft and slippery. This is because in between the layers, weak forces are present (Van der Waal's forces) and the layers of atoms can slide over each another.

1. As electrodes in electrolysis.

2. As a dry lubricant, since graphite is slippery and has a high melting point.

Diamond forms a giant molecular structure consisting of many strong covalent bonds arranged in a vast tetrahedral network.

A large amount of energy is required to break these strong covalent bonds.

This explains why Diamond has a very high melting point of 3500℃ and has an even higher melting point of 4800℃.

Each carbon atom is covalently bonded to four other carbon atoms in a vast network.