Group I Properties (Cambridge (CIE) IGCSE Combined Science): Revision Note

Group I properties & trends: basics

• The Group I metals are called the alkali metals

  • This is because they form alkaline solutions (with high pH values) when reacted with water

• Group I metals include:

  • Lithium, Li

  • Sodium, Na

  • Potassium, K

• 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

    • They get softer down the Group

  • Have shiny silvery surfaces when freshly cut

  • Conduct heat and electricity

  • Have low melting points compared to other metals

    • The melting point generally decreases as you move down the Group

    • Some would melt on a hot day

  • Have low densities compared to other metals

  

Chemical properties of the Group I metals

• They react readily with oxygen and water vapour in air

  • This is why they are stored under oil, to stop them from reacting

• Group I metals will react similarly with water

  • They react to form an alkaline metal hydroxide solution and hydrogen gas

2M (s) + 2H₂O (l)  → 2MOH (aq) + H₂ (g)

• The Group I metals get more reactive as you move down the group

  • Only the first three metals are allowed in schools for demonstrations

Reactions of the Group I metals and water

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

General trends of the Group I metals

• As you move down the group:

  • Melting point decreases

  • Density increases

    • There is an exception in the early part of the group

  • Reactivity (with water) increases

Predicting the Properties of Group I Elements

Extended tier only

• 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

• The reactivity of alkali metals increases down the group

• This means that rubidium, caesium and francium will react more vigorously with air and water than lithium, sodium and potassium

  • Lithium will be the least reactive metal at the top of the group

  • 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

Rubidium

• Predicted observations:

  • Very violent reaction

  • May explode with sparks

Caesium

• Predicted observations:

  • Extremely violent reaction

  • Can explode due to rapid production of heat and hydrogen

Francium

• Predicted observations:

  • Extremely reactive

  • Difficult to confirm experimentally due to rarity and radioactivity

You can use any given data for Group 1 elements to identify trends and make predictions about other elements in the group.