Group 1 (AQA GCSE Combined Science: Synergy: Physical Sciences): Revision Note

Group 1 elements - the alkali metals

• The Group 1 elements are known as the alkali metals

• They are found in the first column of the periodic table:

• They share similar chemical properties because they each have one electron in their outer shell

Group 1 properties

• The properties of Group 1 metals include:

  • Soft - these metals can easily be cut with a knife

  • Low density - the first three alkali metals are less dense than water

  • Low melting points compared to most metals

  • Very reactive - they only need to lose one electron to achieve a stable outer shell

  • React with water to form hydroxides that give alkaline solutions

    • This is why they are called the alkali metals

  • React with non-metals - this includes oxygen and chlorine to form ionic compounds

Reactions with water

• The alkali metals react vigorously with water, producing a metal hydroxide and hydrogen gas

• Reactions become more vigorous going down the group

• The alkali metals are stored in oil to prevent them from reacting with oxygen or water vapour in the air

Lithium

lithium + water → lithium hydroxide + hydrogen 

2Li (s) + 2H₂O (l) → 2LiOH (aq) + H₂ (g)

• Observations:

  • Relatively slow reaction

  • Fizzing

  • Lithium moves on the surface of the water 

Sodium

sodium + water → sodium hydroxide + hydrogen 

2Na (s) + 2H₂O (l) → 2NaOH (aq) + H₂ (g)

• Observations:

  • More vigorous fizzing 

  • Moves rapidly on the surface of the water

  • Dissolves quickly 

Potassium

potassium + water → potassium hydroxide + hydrogen 

2K (s) + 2H₂O (l) → 2KOH (aq) + H₂ (g)

• Observations:

  • Reacts more vigorously than sodium 

  • Burns with a lilac flame 

  • Moves very rapidly on the surface 

  • Dissolves very quickly

Reactions with oxygen

• The alkali metals react with oxygen in the air forming metal oxides

  • This causes them to tarnish when exposed to the air

• The metal oxide produced is a dull coating which covers the surface of the metal

Lithium

lithium + oxygen → lithium oxide 

4Li (s)  +  O₂ (g)   →   2Li₂O (s)

Sodium

sodium + oxygen → sodium oxide 

4Na (s)  +  O₂ (g)   →   2Na₂O (s)

Potassium

potassium  + oxygen →  potassium oxide 

4K (s)  +  O₂ (g)   →   2K₂O (s)

Reactions with chlorine

• All the group 1 metals react vigorously with chlorine gas when heated

  • They form metal chloride salts

• Thiese reactions become more vigorous going down the group

Lithium

lithium  + chlorine →   lithium chloride

2Li (s) + Cl₂ (g) → 2LiCl (s)

Sodium

sodium  + chlorine →   sodium chloride

2Na (s) + Cl₂ (g) → 2NaCl (s)

Potassium

potassium  + chlorine →   potassium chloride

2K (s) + Cl₂ (g) → 2KCl (s)

Group 1 reactivity

Physical trends

• The alkali metals are soft and get softer going down the group

• Their densities are low

• They have relatively low melting points, which decrease going down the group

  • The is due to decreasing attractive forces between outer electrons and positive ions

Reactivity trend

• Reactivity increases going down Group 1

• When a Group 1 metal reacts:

  • It loses the 1 electron in its outer shell

  • It forms a 1+ ion

• Going down the group:

  • Atoms have more electron shells

  • So, the outer electron is further from the nucleus

  • This menas that the force of attraction between the nucleus and the outer electron is weaker

  • Therefore, less energy is needed to remove the outer electron, and it is lost more easily

• This is why reactivity increases going down Group 1

Electronic structures of the first three alkali metals