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Edexcel IGCSE Chemistry Your notes

Group 1 (Alkali Metals)

Contents
Group 1 (Alkali Metals)
Group 1: Reactivity & Electronic Configurations

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Group 1 (Alkali Metals)

Your notes
Group 1 elements
The Group 1 metals 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

Reaction with water

The reaction of the Group 1 metals with water provides evidence for categorising these elements into
the same chemical family
The general pattern shown is:

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Group 1 metal + water ⟶ metal hydroxide + hydrogen

2M (s) + 2H2O (l) ⟶ 2MOH (aq) + H2 (g) Your notes

where M is Li, Na, K, Rb or Cs
The hydroxides formed all have the same general formula and are colourless, aqueous solutions
The metals are so named because they form alkalis in water

Examiner Tip
Remember the Group 1 metals all produce alkaline solutions (>pH 7) when they react with water.
Lithium will produce a solution of lithium hydroxide; sodium will produce a solution of sodium
hydroxide and so on. Make sure you can give the reaction equations with the correct state symbols to
show what is happening during the reactions!

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Trends in Group 1
Your notes
The differences between the reactions of the group 1 metals with water and oxygen provide evidence
of trends within the group

Reactions with water

The reactions of the alkali metals with water get more vigorous as you descend the group
Summary of the reactions of the first three alkali metals with water

Element Reaction Observations

lithium + water → lithium hydroxide + hydrogen Relatively slow reaction

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

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
The metal tarnish more rapidly as you go down the group
Summary of the reactions of the first three alkali metals with oxygen

Element Reaction

lithium + oxygen → lithium oxide

Li
4Li (s) + O2 (g) → 2Li2O (s)

Na sodium + oxygen → sodium oxide

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4Na (s) + O2 (g) → 2Na2O (s)

potassium + oxygen → potassium oxide Your notes

K
4K (s) + O2 (g) → 2K2O (s)

Physical trends
Apart from the chemical trends there are also patterns to be seen in the physical properties
The alkali metals are soft and easy to cut, getting softer as you move down the group
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
Graph to show the physical trends in Group 1

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

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Examiner Tip
Your notes
Trends are patterns of behaviour that change as you go down a group or across a period. Trends are
not the same as rules, so sometimes there are odd properties that seem inconsistent, but the overall
patterns remain the same.

Predicting properties in Group 1

Following these trends, we can say that:
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)
Using the information given in the trends we would predict that rubidium:
would be a soft grey solid
appears shiny when freshly cut
is more dense than potassium (> 0.86 g cm-3)
has a lower melting point than potassium (< 63.5 oC)

Examiner Tip
You could be asked to make predictions about how rubidium would be expected to react with water,
knowing that it lies below potassium in group 1. Words like 'explosively' and 'violently' would be good
ones to choose when describing the reaction.

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Group 1: Reactivity & Electronic Configurations

Your notes
Electronic configuration of Group 1 elements
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 electron, as there is only 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
ion 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

Electronic configuration 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

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Examiner Tip
Your notes
In your exams, you could be asked to explain the trend in reactivity of the alkali metals - make sure you
answer this question using their electronic configuration to support your answer.

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