The Periodic Table

State and explain the variation in bonding in oxides in terms of electronegativity

1. Na2O, MgO and Al2O3 form ionic compounds due to the large differences in electronegativity between between the elements and that of oxygen.

2. SiO2, P4O10 and SO3 form covalent compounds due to the small differences in electronegativity between the elements and that of oxygen.

Describe and explain the reaction of Na2O with water

1. Na2O reacts vigorously with water to form a strongly alkaline solution of NaOH(aq). The pH= 13 and universal indicator turns violet.

2. Na2O(s) + H2O(l)—> 2NaOH(aq).

Describe and explain the reaction of MgO with water

1. MgO reacts with water to a very small extent due to its high lattice energy to form a sparingly soluble solution of Mg(OH)2(aq). The pH= 9 and universal indicator turns blue.

2. Formation of ion dipole interactions between MgO molecules and water molecules releases insufficient energy to overcome stronger ionic bonds between Mg2+ and O2- and hydrogen bonds between water molecules.

3. MgO(s) + H2O(l) reversible Mg(OH)2(aq).

Describe and explain the reaction of Al2O3 with water

1. Al2O3 does not react with water due to its high lattice energy. The pH= 7 and universal indicator is green.

2. Formation of ion dipole interacts between Al2O3 molecules and water molecules releases insufficient energy to overcome stronger ionic bonds between Al3+ and O2- and hydrogen bonds between water molecules.

Describe and explain the reaction of SiO2 with water

1. SiO2 does not react with water due to its giant molecular structure. The pH= 7 and universal indicator is green.

2. Formation of instantaneous dipole induced dipole attractions between SiO2 molecules and water molecules releases insufficient energy to overcome strong covalent bonds between Si and O atoms and hydrogen bonds between water molecules.

Describe and explain the reaction of P4O10 with water

1. P4O10 reacts vigorously with water to form a strongly acidic solution of H3PO4(aq). The pH= 2 and universal indicator turns red.

2. P4O10(s) + 6H2O(l)—> 4H3PO4(aq).

Describe and explain the reaction of SO3 with water

1. SO3 reacts vigorously with water to form a strongly acidic solution of H2SO4(aq). The pH= 1 and universal indicator turns red.

2. SO3(g) + H2O(l)—> H2SO4(aq).

Describe the base behaviour of Na2O and NaOH

1. Na2O is a basic oxide and reacts vigorously with an acid to form salt and water.

2. Na2O(s) + 2HCl(aq)—> 2NaCl(aq) + H2O(l).

3. NaOH is a base and reacts with an acid to form salt and water.

4. NaOH(aq) + HCl(aq)—> NaCl(aq) + H2O(l).

Describe the base behaviour of MgO and Mg(OH)2

1. MgO is a basic oxide and reacts with an acid to form salt and water.

2. MgO(s) + 2HCl(aq)—> MgCl2(aq) + H2O(l).

3. Mg(OH)2 is a base and reacts with an acid to form salt and water.

4. Mg(OH)2(aq) + 2HCl(aq)—> MgCl2(aq) + 2H2O(l).

Describe the amphoteric behaviour of Al2O3 and Al(OH)3

1. Al2O3 is mainly ionic with partial covalent character, hence it is amphoteric. It reacts with an acid to form salt and water, hence behaving as a basic oxide. It reacts with a base to form salt, hence behaving as an acidic oxide.

2. Al2O3(s) + 6HCl(l)—> AlCl3(aq) + 3H2O(l).

3. Al2O3(s) + 2NaOH(aq) + 3H2O(l)—> 2NaAl(OH)4(aq).

4. Al(OH)3 reacts with an acid to form salt and water, hence behaving as a basic oxide. It reacts with base to form salt, hence behaving as an acid.

5. Al(OH)3(s) + 3HCl(aq)—> AlCl3(aq) + 3H2O(l).

6. Al(OH)3(s) + NaOH(aq)—> NaAl(OH)4(aq).

Describe the acidic behaviour of SiO2

1. SiO2 is insoluble in an alkali under normal conditions. It is an acidic oxide and reacts with molten NaOH at high temperature to form silicate salt.

2. SiO2 + 2NaOH(l) molten—>350 Na2SiO3(l) + H2O(g).

Describe the acidic behaviour of P4O10

1. P4O10 is an acidic oxide and reacts with a base to form salt and water.

2. P4O10(s) + 12NaOH(aq)—> 4Na3PO4(aq) + 6H2O(l).

Describe the acidic behaviour of P4O10

1. SO3 is an acidic oxide and reacts with a base to form salt and water.

2. SO3(g) + 2NaOH(aq)—> Na2SO4(aq) + H2O(l).

State and explain the variation in bonding in chlorides in terms of electronegativity

1. NaCl and MgCl2 form ionic compounds due to the large difference in electronegativity between the elements and that of chlorine.

2. SiCl4 and PCl5 form covalent compounds due to the small difference in electronegativity between the elements and that of chlorine.

3. AlCl3 is ionic with a large degree of covalency.

State and explain the variation in bonding in chlorides in terms of electronegativity

1. NaCl and MgCl2 form ionic compounds due to the large difference in electronegativity between the elements and that of chlorine.

2. SiCl4 and PCl5 form covalent compounds due to the small difference in electronegativity between the elements and that of chlorine.

3. AlCl3 is ionic with a large degree of covalency.

Describe and explain the reaction of MgCl2 with water

1. Hydration occurs: MgCl2(s) + 6H2O(l)—> [Mg(H2O)6]2+(aq) + 2Cl-(aq).

2. Slight hydrolysis occurs due to the higher charge density of Mg2+: [Mg(H2O)6]2+ reversible [Mg(H2O)5OH]+(aq) + H+(aq).

3. The pH=6.5.

Describe and explain the reaction of AlCl3 with water

When a large amount of water is added:

1. Hydration occurs: AlCl3(s) + 6H2O(l)—> [Al(H2O)6]3+(aq) + 3Cl-(aq).

2. Hydrolysis occurs due to the higher charge density of Al3+. Al3+ has high polarising power and draws electrons away from its surrounding water molecules and weakens the O-H bonds to produce H+ in solution: Al[(H2O)6]3+(aq) reversible Al[(H2O)5OH]2+(aq) + H+(aq).

3. The pH= 3.

When a few drops of water is added,

1. AlCl3(s) + 3H2O(l)—> Al(OH)3(s) + 3HCl(g).

Describe and explain the reaction of SiCl4 with water

1. Complete hydrolysis occurs due to the energetically accessible and vacant 3d orbital available for dative bonding with water molecules: SiCl4(l) + 2H2O(l)—> SiO2(s) + 4HCl(aq).

2. The pH= 1.

Describe and explain the reaction of PCl5 with water

1. Complete hydrolysis occurs due to the energetically accessible and vacant 3d orbital available for dative bonding with water molecules: PCl5(s) + 4H2O(l)—> H3PO4(aq) + 5HCl(aq).

2. The pH= 1.

3. When PCl5:H2O= 1:1/ water is cold/ water in limited amount: PCl5(s) + H2O(l)—> POCl3(l) + 2HCl(g).

4. When excess water is added: POCl3(l) + 3H2O(l)—> H3PO4(aq) + 3HCl(aq).