Group 1: The Alkali Metals

This lesson covers Group 1 of the periodic table — the alkali metals — as required by AQA GCSE Chemistry specification (5.1.2). Group 1 elements are some of the most reactive metals. Understanding their properties, reactions, and the trend in reactivity down the group is essential for GCSE Chemistry.

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The Alkali Metals

Group 1 contains the following elements:

Element	Symbol	Atomic Number	Electronic Configuration	Melting Point (degrees C)	Density (g/cm3)
Lithium	Li	3	2, 1	181	0.53
Sodium	Na	11	2, 8, 1	98	0.97
Potassium	K	19	2, 8, 8, 1	63	0.86
Rubidium	Rb	37	2, 8, 18, 8, 1	39	1.53
Caesium	Cs	55	2, 8, 18, 18, 8, 1	28	1.93
Francium	Fr	87	(radioactive, very rare)	—	—

Why Are They Called "Alkali" Metals?

They are called alkali metals because they react with water to form alkaline solutions (solutions with pH greater than 7). The metal hydroxides produced are strong alkalis.

Exam Tip: Do not confuse "alkali metals" with "alkaline earth metals" (Group 2). Group 1 are the alkali metals. They are called this because they react with water to produce alkaline hydroxide solutions, NOT because they are found in alkaline conditions.

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Physical Properties of Alkali Metals

Group 1 metals have unusual physical properties for metals:

Property	Description
Softness	Alkali metals are very soft and can be cut with a knife. When freshly cut, they have a shiny surface that quickly tarnishes.
Low density	Lithium, sodium and potassium are less dense than water — they float on water.
Low melting and boiling points	Compared to most metals, alkali metals have relatively low melting points. Melting point decreases down the group.
Good conductors	Like all metals, they conduct electricity and heat well.
Stored under oil	They are so reactive with air and water that they must be stored under mineral oil to prevent reactions.

Trends in Physical Properties Down Group 1

Property	Trend Down the Group	Explanation
Melting point	Decreases	Metallic bonds weaken as atoms get larger and the delocalised electrons are further from the positive ions
Density	Generally increases (lithium is an exception)	Atoms have more mass; the increase in mass outweighs the increase in volume
Hardness	Decreases	Metallic bonds are weaker, so the metal is easier to cut

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Reactions of Alkali Metals

1. Reaction with Water

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

General word equation: Alkali metal + Water → Metal hydroxide + Hydrogen

General symbol equation (using M for any Group 1 metal): 2M + 2H2O → 2MOH + H2

Metal	Observation	Reactivity
Lithium	Fizzes gently on the surface, moves around slowly, dissolves gradually	Least reactive
Sodium	Fizzes vigorously, melts into a silvery ball, moves rapidly on the surface, may produce a yellow flame	More reactive
Potassium	Fizzes very vigorously, produces a lilac/purple flame, may spit or explode, moves very quickly	Most reactive (of those commonly demonstrated)

The solutions produced are alkaline — they turn universal indicator purple/blue and have a pH greater than 7.

Specific equations:

• 2Li + 2H2O → 2LiOH + H2
• 2Na + 2H2O → 2NaOH + H2
• 2K + 2H2O → 2KOH + H2

Exam Tip: The reaction of potassium with water is particularly dramatic — it produces a lilac flame. Rubidium and caesium are even more reactive and would explode on contact with water. You must be able to describe the trend: reactivity increases down Group 1.

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Reaction with Oxygen

Alkali metals react with oxygen in the air to form metal oxides. This is why they tarnish rapidly when cut.

General equation: 4M + O2 → 2M2O

• 4Li + O2 → 2Li2O (lithium oxide — white powder)
• 4Na + O2 → 2Na2O (sodium oxide — white powder)
• 4K + O2 → 2K2O (potassium oxide — white/yellow powder)

Reaction with Chlorine

Alkali metals react vigorously with chlorine to form metal chlorides (white crystalline salts).

General equation: 2M + Cl2 → 2MCl

• 2Na + Cl2 → 2NaCl (sodium chloride)
• 2K + Cl2 → 2KCl (potassium chloride)

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Explaining the Trend in Reactivity

Reactivity increases down Group 1. This is explained by atomic structure:

graph TD
    A["Going Down Group 1"] --> B["More electron shells"]
    B --> C["Outer electron is further from the nucleus"]
    B --> D["Greater electron shielding"]
    C --> E["Weaker attraction between nucleus and outer electron"]
    D --> E
    E --> F["Outer electron is lost more easily"]
    F --> G["More reactive"]

    style A fill:#2c3e50,color:#fff
    style E fill:#e74c3c,color:#fff
    style G fill:#27ae60,color:#fff

Detailed Explanation

• All Group 1 elements have 1 electron in their outer shell. They react by losing this electron to form a +1 ion (e.g. Na → Na+ + e-).
• Going down the group, atoms have more electron shells, so the outer electron is further from the nucleus.
• There is also greater shielding from the inner electrons, which reduces the attraction between the positively charged nucleus and the outer electron.
• This means the outer electron is easier to remove (less energy is needed).
• Therefore, the element is more reactive.

Exam Tip: When explaining why reactivity increases down Group 1, you need three key points: (1) more electron shells, (2) outer electron further from the nucleus with greater shielding, (3) outer electron is easier to lose. All three points are needed for full marks. Do NOT just say "bigger atom" — explain WHY that matters.

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Alkali Metals and Ions

When Group 1 metals react, they always form +1 ions by losing their single outer electron: