Group I Properties (Cambridge (CIE) O Level Chemistry): Revision Note

Group I Properties & Trends: Basics

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

Lithium

• Reaction equation:

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

• Slower reaction than sodium

• Bubbles of hydrogen gas

• Lithium moves around the surface of the water

  • Floats on water because it is less dense

Sodium

• Reaction equation:

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

• Bubbles of hydrogen gas

• Sodium melts into a shiny ball that moves around the surface of the water

  • Floats on water because it is less dense

• Melts because sodium has a low melting point and a lot of heat is released in the reaction

• Hydrogen is evolved, which causes the ball of sodium to move around the surface of the water

• A white trail of sodium hydroxide is produced, which dissolves in the water, producing an alkaline solution

Potassium

• Reaction equation:

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

• Reacts more violently than sodium

• Bubbles of hydrogen gas

• Melts into a shiny ball that dashes around the surface

• Burns with a lilac flame

• A white trail of potassium hydroxide is produced, which dissolves in the water, producing an alkaline solution

Predicting the Properties of Group I Elements

• 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