Physical properties of the group 7 elements

Group 7 contains non-metal elements placed in a vertical column on the right of the periodic table. The elements in group 7 are called the halogens.

Periodic table with Group 7 halogens coloured in red.Group 7 is on the right-hand side of the periodic table, next to group 0

The halogens show trends in their physical and chemical properties.

Physical properties

The table shows the colour and physical states of chlorine, bromine and iodine at room temperature and pressure.

Group 7 elementColourState Colour in gas state
Chlorine, Cl2Yellow-greenGasYellow-green
Bromine, Br2Deep-redLiquidRed-brown
Iodine, I2Grey SolidPurple

The melting points and boiling points of the halogens increase going down group 7, and their colour gets darker.

The group 7 elements exist as diatomic molecules. Their chemical formulae are F2, Cl2, Br2 and I2.

The bond between the atoms in a molecule is very strong, but the forces of attraction between molecules are weak. This explains why group 7 elements have low boiling points.

Question

The graph shows the melting and boiling points of the first four group 7 elements. Astatine is placed below iodine in group 7. Predict the melting and boiling points of astatine, and its state at room temperature.

Bar chart showing how the melting and boiling points of the halogens increase going down group 7

Astatine should have a melting point of about 300°C and a boiling point of about 340°C. This means that it will be solid at room temperature. (Actual boiling point is 350°C.)