Group I Properties (Cambridge O Level Chemistry)

The Group I metals

• The Group I metals are also called the alkali metals as they form alkaline solutions with high pH values when reacted with water
• Group I metals are lithium, sodium, potassium, rubidium, caesium and francium
• They all contain just one electron in their outer shell

Physical properties of the Group I metals

• The Group I metals:
  • Are soft and easy to cut, getting even softer and denser as you move down the Group (sodium and potassium do not follow the trend in density)
  • Have shiny silvery surfaces when freshly cut
  • Conduct heat and electricity
  • They all have low melting points and low densities compared to other metals, and the melting point decreases as you move down the Group; some would melt on a hot day
  

The alkali metals lie on the far left-hand side of the Periodic Table

Chemical properties of the Group I metals

• They react readily with oxygen and water vapour in air so they are stored under oil to stop them from reacting
• Group I metals will react similarly with water, reacting vigorously to produce an alkaline metal hydroxide solution and hydrogen gas
• The Group I metals get more reactive as you look down the group, so only the first three metals are allowed in schools for demonstrations

Reactions of the Group I metals and water

• Knowing the reactions of elements at the top of the group allows you to predict the properties of other elements further down Group I

Properties of other Alkali Metals (Rubidium, Caesium and Francium)

• As the reactivity of alkali metals increases down the group, rubidium, caesium and francium will react more vigorously with air and water than lithium, sodium and potassium
• Lithium will be the least reactive metal in the group at the top, and francium will be the most reactive at the bottom
• Francium is rare and radioactive so is difficult to confirm predictions
• For example the reactions with water can be predicted:

Predicting the Reaction with Water

• You can also look at other properties such as boiling point, melting point and density of Group I elements and use them to predict whether the other properties are likely to be larger or smaller going down the group