Group 1

Group 1 contains elements placed in 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 elements coloured in red.Group 1 is on the left-hand side of the periodic table

The alkali metals share similar physical properties. For example, they:

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

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

ElementMelting point (°C)
Lithium, Li180
Sodium, Na98
Potassium, K63
Rubidium, Rb39
Caesium, Cs28

Going down group 1, the melting point decreases.

Chemical properties of group 1 elements

Atoms of group 1 elements all have one electron in their outer shell. This means that the alkali metals all have similar chemical properties.

When a group 1 element takes part in a reaction, its atoms each lose one electron. This forms positively charged ions. The ions have a stable arrangement of electrons, with a complete outer shell.

Reactions with water

The alkali metals react with water to produce a metal hydroxide and hydrogen. For example, sodium reacts with water:

sodium + water → sodium hydroxide + hydrogen

2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

Sodium hydroxide is an alkali. It is a base that dissolves in water to form an alkaline solution. This solution:

Question

Complete the word equation and balanced symbol equation for the reaction of potassium with water.

potassium + water → ______________ + ______________

2 ___(s) + 2H2O(l) → ___KOH(aq) + ______(g)

potassium + water → potassium hydroxide + hydrogen

2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)

Reactions compared

The table shows observations when lithium, sodium and potassium are added to water. The reactivity of these metals increases going down the group.

ElementObservation when added to water
Lithium, LiFizzes steadily; slowly becomes smaller until it disappears
Sodium, NaFizzes rapidly; melts to form a ball; quickly becomes smaller until it disappears
Potassium, KBurns violently with sparks and a lilac flame; quickly melts to form a ball; disappears rapidly, often with a small explosion
The reaction of potassium with water gives a lilac flame
The reaction of potassium with water gives a lilac flame

Question

Rubidium is placed below potassium in group 1. Predict what is seen when rubidium is added to water.

Rubidium melts very quickly. It burns violently and explodes.

Reactions with oxygen

The group 1 elements react with oxygen from the air to make metal oxides.

At room temperature, oxygen reacts with the surface of the metal. This forms a white oxide, which covers the surface. The metal below the surface does not react.

The alkali metals burn vigorously when heated and placed in a gas jar of oxygen. The oxide forms as white smoke.

For example:

sodium + oxygen → sodium oxide

4Na(s) + O2(g) → 2Na2O(s)

The reactivity of the group 1 elements increases down the group, so their reactions with oxygen get more vigorous.

Question

Predict which becomes white more quickly on exposure to air - a piece of rubidium, or a piece of lithium. Explain your answer.

The rubidium becomes white more quickly. This is because rubidium is below lithium in group 1, so rubidium is more reactive and so it reacts with the oxygen in the air to form an oxide layer more quickly.

Reactions with chlorine

The group 1 elements react vigorously with chlorine. The products of the reactions are chlorides. At room temperature the chlorides are white solids. They dissolve in water to form colourless solutions. For example:

sodium + chlorine → sodium chloride

2Na(s) + Cl2(g) → 2NaCl(s)

The reactions with chlorine get more vigorous going down the group.

Question

Balance the equation for the reaction of potassium with chlorine.

_____K(s) + Cl2(g) → _____KCl(s)

2K(s) + Cl2(g) → 2KCl(s)

Explaining the trend in reactivity

When a group 1 element takes part in a reaction, each of its atoms loses its outer electron to form a positively charged ion. The more easily the ions form, the more reactive the metal.

Going down group 1:

  • the atoms become larger
  • the outer electron becomes further from the nucleus
  • the force of attraction between the nucleus and the outer electron decreases
  • the outer electron is lost more easily
Table showing electronic structures of group 1 elements, lithium, sodium and potassium. Group 1 elements have similar properties and reactions as they all have one electron in their outer shell.