Physical properties of the alkali metals

Group 1 is a vertical column on the far left of the periodic table. The elements in group 1 are called the alkali metals.

Periodic table with Group 1 metals coloured in red.Group 1 is on the left-hand side of the periodic table

The alkali metals share similar physical and chemical properties.

Physical properties

The alkali metals:

  • are soft (they can be cut with a knife)
  • have relatively low melting points

The alkali metals also have low densities. They are low enough for the first three (lithium, sodium and potassium) to float on water.

Example

Group 1 elementMelting point (°C)
Lithium, Li180
Sodium, Na98
Potassium, K63
Rubidium, Rb39
Caesium, Cs28
Question

The table above shows the melting points of five alkali metals. Use this information to describe how melting point changes in group 1.

Going down group 1, the melting point decreases.

Question

Use the information in the table to predict the melting point of francium, Fr. Explain your answer.

The melting point of francium will be around 27°C. This is because francium is below caesium in the periodic table, so it should have a lower melting point, and the difference in melting point decreases going down from one element to the next.