Group 1: The Alkali Metals

This lesson covers the properties, trends and reactions of the Group 1 elements (the alkali metals), as required by the Edexcel GCSE Combined Science specification (1SC0). You need to know their physical and chemical properties, how reactivity changes down the group, and the reactions of lithium, sodium and potassium with water and oxygen.

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The Group 1 Elements

The alkali metals are the elements in Group 1 of the periodic table. The ones you need to know for GCSE are:

Element	Symbol	Atomic Number	Electron Configuration
Lithium	Li	3	2, 1
Sodium	Na	11	2, 8, 1
Potassium	K	19	2, 8, 8, 1
Rubidium	Rb	37	2, 8, 18, 8, 1
Caesium	Cs	55	2, 8, 18, 18, 8, 1
Francium	Fr	87	(radioactive, very rare)

All Group 1 elements have one electron in their outer shell. This single outer electron is the key to understanding their chemistry.

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Physical Properties of Group 1 Metals

Compared to most other metals, the alkali metals have some unusual physical properties:

Property	Group 1 Metals	Typical Metals
Hardness	Soft — can be cut with a knife	Hard
Density	Low — Li, Na and K float on water	High
Melting point	Low for metals	High
Appearance	Shiny when freshly cut (but tarnish quickly in air)	Shiny

Trends in Physical Properties Down Group 1

Property	Trend Down Group 1
Melting point	Decreases
Boiling point	Decreases
Density	Generally increases
Hardness	Decreases (softer)

Exam Tip: Be careful — although melting point decreases down Group 1, reactivity increases. These are two separate trends and they go in opposite directions.

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Why Are Group 1 Metals So Reactive?

Group 1 metals react by losing their single outer electron to form a positive ion with a +1 charge:

Na → Na⁺ + e⁻

The ease with which this electron is lost determines the reactivity.

Why Reactivity Increases Down Group 1

As you go down the group:

1. The atoms get larger — there are more electron shells.
2. The outer electron is further from the nucleus.
3. There is more shielding from inner electron shells.
4. The attraction between the nucleus and the outer electron is weaker.
5. Therefore the outer electron is easier to lose → the metal is more reactive.

graph TD
    A["Going down Group 1"] --> B["More electron shells"]
    B --> C["Outer electron further<br/>from nucleus"]
    C --> D["Weaker attraction<br/>to nucleus"]
    D --> E["Outer electron<br/>lost more easily"]
    E --> F["Reactivity<br/>INCREASES"]

    style A fill:#2c3e50,color:#fff
    style B fill:#2980b9,color:#fff
    style C fill:#2980b9,color:#fff
    style D fill:#e67e22,color:#fff
    style E fill:#e67e22,color:#fff
    style F fill:#c0392b,color:#fff

Exam Tip: When explaining trends in reactivity, always mention the distance of the outer electron from the nucleus and the weaker attraction due to increased shielding. Simply saying "it has more shells" is not a complete answer.

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Reactions of Group 1 Metals with Water

All Group 1 metals react vigorously with cold water to produce a metal hydroxide and hydrogen gas.

General Word Equation

alkali metal + water → metal hydroxide + hydrogen

General Symbol Equation

2M(s) + 2H₂O(l) → 2MOH(aq) + H₂(g)

(where M represents any Group 1 metal)

Specific Reactions

Lithium + water:

• Lithium floats on the water and fizzes gently.
• It moves around the surface as hydrogen gas is released.
• The solution becomes alkaline (a hydroxide is formed).
• 2Li(s) + 2H₂O(l) → 2LiOH(aq) + H₂(g)

Sodium + water:

• Sodium floats, melts into a silvery ball and fizzes vigorously.
• It moves quickly across the surface.
• May ignite with an orange/yellow flame if it gets trapped.
• The solution becomes alkaline.
• 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

Potassium + water:

• Potassium floats, melts and catches fire immediately with a lilac flame.
• It fizzes violently and may spit.
• The reaction is much more vigorous than with sodium or lithium.
• The solution becomes alkaline.
• 2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g)

Comparing the Reactions

Metal	Vigour of Reaction	Flame?	Observation
Lithium	Gentle fizzing	No	Floats, moves slowly
Sodium	Vigorous fizzing	Sometimes (orange/yellow)	Melts into a ball, moves quickly
Potassium	Very vigorous	Yes (lilac)	Catches fire immediately, spits

This clearly shows that reactivity increases down the group: Li < Na < K.

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Reactions of Group 1 Metals with Oxygen

Group 1 metals react with oxygen in the air to form metal oxides. This is why they tarnish quickly when cut.

General Equation

4M(s) + O₂(g) → 2M₂O(s)

Specific Examples

• Lithium: Burns with a crimson red flame → lithium oxide (Li₂O)
• Sodium: Burns with a bright orange/yellow flame → sodium oxide (Na₂O)
• Potassium: Burns with a lilac flame → potassium oxide (K₂O)

The metals must be stored in oil to prevent them reacting with oxygen and water in the air.

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Storage of Group 1 Metals

Because alkali metals are so reactive, they must be stored carefully:

• Stored under oil to prevent contact with air (oxygen) and moisture (water).
• Handled with tongs or forceps — never with bare hands.
• Cut with a knife (they are soft enough) to expose the shiny surface underneath the oxide layer.

Exam Tip: If asked why Group 1 metals are stored in oil, explain that it prevents them reacting with oxygen and water vapour in the air. They would otherwise tarnish or react vigorously.

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Summary