Group 1: The Alkali Metals (AQA GCSE Chemistry)

• The Group 1 elements are known as the alkali metals
  • They form alkaline solutions when they react with water

• The Group 1 metals are lithium, sodium, potassium, rubidium, caesium and francium and they are found in the first column of the periodic table
• The alkali metals share similar characteristic chemical properties because they each have one electron in their outermost shell
• Some of these properties are:
  • They are all soft metals which can easily be cut with a knife
  • They have relatively low densities and low melting points
  • They are very reactive (they only need to lose one electron to become highly stable)

Group 1 elements in the Periodic Table

The alkali metals lie on the far left of the periodic table, in the very first group 

• The alkali metals are soft and easy to cut, getting softer as you move down the group
  • Potassium is the exception; it has a lower density than sodium
• The first three alkali metals are less dense than water
• They all have relatively low melting points which decrease as you move down the group, due to decreasing attractive forces between outer electrons and positive ions

Melting points of the Group 1 elements

The melting point of the Group 1 metals decreases as you descend the group

• The reactivity of the Group 1 metals increases as you go down the group
• When a Group 1 element reacts, its atoms only need to lose the 1 electron in the outer shell
  • When this happens, 1+ ions are formed

• The next shell down automatically becomes the outermost shell and since it is already full, a Group 1 atom obtains noble gas configuration
• As you go down Group 1, the number of shells of electrons increases by 1
  • This means that the outermost electron gets further away from the nucleus, so there are weaker forces of attraction between the outermost electron and the nucleus
  • Less energy is required to overcome the force of attraction as it gets weaker, so the outer electron is lost more easily
  • So, the alkali metals get more reactive as you descend the group

The electronic structure of Group 1 elements

These electron shell diagrams of the first 3 alkali metals show that the group 1 metals have 1 electron in their outer shell

• You need to be able to describe the reactions of the first three alkali metals with water, oxygen and chlorine
  • This includes providing reaction equations to show what is happening

• Alkali metals react readily with oxygen and water vapour in air, so they are usually stored in oil to stop them from reacting

Reactions with Water

• The reactions of the alkali metals with water get more vigorous as you descend the group, as with the other reactions
• You could be asked to describe and explain the reactions of the alkali metals with water

Summary of the Reactions of the First Three Alkali Metals with Water

Element	Reaction	Observations
Li	lithium  + water   →   lithium hydroxide  +  hydrogen  2Li (s)  +  2H2O (l)   →   2LiOH (aq)  +   H2 (g)	Relatively slow reaction Fizzing Lithium moves on the surface of the water
Na	sodium + water   →   sodium hydroxide  +  hydrogen  2Na (s)  +  2H2O (l)   →   2NaOH (aq)   +   H2 (g)	More vigorous fizzing  Moves rapidly on the surface of the water Dissolves quickly
K	potassium  + water   →   potassium hydroxide  +  hydrogen  2K (s)  +  2H2O (l)   →   2KOH (aq)  +   H2 (g)	Reacts more vigorously than sodium  Burns with a lilac flame  Moves very rapidly on the surface  Dissolves very quickly

• Rubidium, caesium and francium will react even more vigorously with air and water than the first three alkali metals
• Of the alkali metals, lithium is the least reactive (as it is at the top of group 1) and francium would be the most reactive (as it’s at the bottom of group 1)

Reactions with Oxygen

• The alkali metals react with oxygen in the air forming metal oxides, which is why the alkali metals tarnish when exposed to the air
• The metal oxide produced is a dull coating which covers the surface of the metal

Summary of the reactions of the first three alkali metals with oxygen

Element	Reaction
Li	lithium + oxygen → lithium oxide  4Li (s)  +  O2 (g)   →   2Li2O (s)
Na	sodium + oxygen → sodium oxide  4Na (s)  +  O2 (g)   →   2Na2O (s)
K	potassium  + oxygen →  potassium oxide  4K (s)  +  O2 (g)   →   2K2O (s)

Reactions with Chlorine

• All the group 1 metals react vigorously when heated with chlorine gas to form salts called metal chlorides
• This reaction becomes more vigorous moving down the group, the same as with the reaction between the metals and water

Summary of the Reactions of the First Three Alkali Metals with Chlorine

Element	Reaction
Li	lithium  + chlorine →   lithium chloride 2Li (s) + Cl2 (g) → 2LiCl (s)
Na	sodium  + chlorine →   sodium chloride 2Na (s) + Cl2 (g) → 2NaCl (s)
K	potassium  + chlorine →   potassium chloride 2K (s) + Cl2 (g) → 2KCl (s)