Halogens and displacement reactions

Last time

Before we start: last time, in Group I metals, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

A gas, a liquid and a solid

Chlorine is a pale green gas. Bromine is a red-brown liquid, and iodine is a grey-black solid. They look nothing alike, yet all three are in Group VII, the halogens, and they react in the same way. A reactive one can even push a less reactive one out of a compound.

The family

The halogens are fluorine, chlorine, bromine, iodine and astatine. All are non-metals. Each has seven outer electrons. They gain one electron to form a one minus ion. They exist as diatomic molecules, with two atoms joined by a covalent bond: Cl 2, Br 2 and I 2.

Appearance

Chlorine is a pale yellow-green gas. Bromine is a red-brown liquid giving off an orange-brown vapour. Iodine is a grey-black solid, and it gives a purple vapour when heated. The colour gets darker, and the state changes from gas to liquid to solid, going down the group.

Trends down the group

The melting point and the boiling point increase going down the group. The density increases going down the group. The reactivity decreases going down the group. Chlorine is more reactive than bromine, and bromine is more reactive than iodine.