Properties of Period 3 elements and their oxides - AL only (3.2.4)

Sodium reacts vigorously with cold water to produce sodium hydroxide and hydrogen:

Magnesium reacts slowly with cold water to produce magnesium hydroxide and hydrogen:

With steam, magnesium reacts vigorously to produce magnesium oxide and hydrogen:

The reactions of Period 3 elements with oxygen show a trend from forming basic ionic oxides to acidic covalent oxides, with the amphoteric (a substance that can act as both an acid and base) marking the transition; this reflects a shift from ionic to covalent bonding, which determines acid–base behaviour.

Sodium and magnesium form basic, ionic oxides:

Aluminium forms an amphoteric oxide:

Silicon forms an acidic, giant covalent oxide:

Phosphorus forms an acidic, molecular oxide:

Sulfur also forms an acidic, molecular oxide:

Then, sulfur dioxide reacts with oxygen to form the acidic sulfur trioxide

and both have high melting points as they are giant ionic lattice structures.

has a higher melting point than .

ions are smaller and more highly charged than ions, leading to stronger electrostatic attractions between the and ions, which require more energy to overcome.

, exhibits a mix of ionic and covalent character.

The strong ionic bonds between and contribute to a high melting point, although the covalent character in its structure makes its melting point less than .

has a giant covalent structure, where strong covalent bonds between silicon and oxygen atoms hold the structure together, resulting in a high melting point.

The network of covalent bonding leads to a strong, stable structure, which requires a lot of energy to overcome.

and , have simple molecular structures with weak intermolecular forces between molecules.

The melting points are lower than those of the giant ionic and giant covalent oxides in Period 3.

, with more electrons and greater polarisability, experiences stronger induced dipole–dipole forces and a higher melting point than , which has fewer electrons. is a gas at room temperature whereas is a solid.

Note that has a permanent dipole, but the difference in molecular size leads to the induced dipole–dipole forces in being larger than the permanent dipole–dipole forces in .

The Period 3 oxides react with water to form solutions with varying , depending on the type of bonding in each oxide.

and are basic oxides with a giant ionic lattice structure. When they react with water, they form alkaline solutions:

is a giant structure with a mix of ionic and covalent character.

is a giant covalent oxide with strong covalent bonds.

Both and are insoluble in water, resulting in a neutral .

and are simple molecular oxides with covalent bonding. They form acidic solutions when they react with water:

Basic oxides like and react with acids to form salts:

Aluminium oxide, is amphoteric and therefore reacts with both acids and bases:

Acidic oxides like , , and react with bases to form salts: