Group 7 - chemical properties

Atoms of group 7 elements all have seven electrons in their outer shell. This means that the halogens all have similar chemical reactions.

When a group 7 element takes part in a reaction, its atoms each gain one electron. These atoms form negatively charged ions. The ions have a stable arrangement of electrons, with a complete outer shell.

Reactions with metals

The halogens react with metals to produce salts. The salts are made up of ions, which are held together by ionic bonds. For example, chlorine reacts with sodium:

sodium + chlorine → sodium chloride

2Na(s) + Cl2(g) → 2NaCl(s)

Sodium and chlorine react vigorously when heated, giving an orange flame and clouds of white sodium chloride.

In group 7, the reactivity of the elements decreases down the group. The table describes what happens when halogens react with iron wool.

FluorineCold iron wool burns to produce white iron(III) fluoride
ChlorineHot iron wool burns vigorously to produce orange-brown iron(III) chloride
BromineHot iron wool burns quickly to produce red-brown iron(III) bromide
IodineHot iron wool reacts slowly in iodine vapour to produce grey iron(II) iodide

Write a balanced equation for the reaction of iron with chlorine to produce solid iron(III) chloride, FeCl3. Include state symbols.

2Fe(s) + 3Cl2(g) → 2FeCl3(s)

Reactions with non-metals

The halogens react with non-metals such as hydrogen. When a halogen reacts with hydrogen, the product is a compound called a hydrogen halide. For example, chlorine reacts with hydrogen:

hydrogen + chlorine → hydrogen chloride

H2(g) + Cl2(g) → 2HCl(g)

The hydrogen halides are gases at room temperature. They dissolve in water to produce acidic solutions. Hydrogen chloride dissolves in water to produce hydrochloric acid, HCl(aq).

The table describes what happens when halogens react with hydrogen. It shows that the reactivity of the elements decreases down the group.

FluorineExplodes at room temperature and in the dark, forming hydrogen fluoride
ChlorineExplodes with a flame or in sunlight, forming hydrogen chloride
BromineVigorous reaction when warmed with hydrogen, forming hydrogen bromide
IodineVery slow reaction when heated strongly, forming some hydrogen iodide

Astatine is below iodine in group 7. Use the information to predict the reaction of astatine with hydrogen.

Astatine should react very slowly with hydrogen, even when heated. A small amount of hydrogen astatide should form, which should dissolve in water to form an acidic solution.