Group 1 — Alkali Metals

This lesson covers the properties and reactions of the Group 1 elements (alkali metals), as required by AQA GCSE Combined Science Trilogy (8464, Chemistry 4.1.2). Group 1 consists of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr). You need to know their properties, reactions with water, and how reactivity changes down the group.

---

Physical Properties of Group 1 Metals

Compared to most metals, the alkali metals are unusual:

Property	Group 1 Metals
Melting point	Relatively low for metals (and decreases down the group)
Density	Relatively low (Li, Na and K are less dense than water — they float)
Hardness	Very soft — can be cut with a knife
Appearance	Shiny when freshly cut, but tarnish rapidly in air

They are stored under oil to prevent them from reacting with oxygen and water vapour in the air.

Exam Tip: If asked "Why are alkali metals stored under oil?", answer: to prevent them from reacting with oxygen and moisture in the air. They are too reactive to be left exposed.

---

Electronic Configuration

All Group 1 elements have one electron in their outer shell:

Element	Symbol	Atomic Number	Configuration
Lithium	Li	3	$2, 1$2,1
Sodium	Na	11	$2, 8, 1$2,8,1
Potassium	K	19	$2, 8, 8, 1$2,8,8,1

When they react, they lose this one outer electron to form a positive ion with a charge of 1+ (e.g. Na⁺, K⁺).

---

Reactions with Water

All Group 1 metals react with cold water to produce a metal hydroxide (an alkali) and hydrogen gas:

$\text{Metal} + \text{Water} \rightarrow \text{Metal hydroxide} + \text{Hydrogen}$Metal+Water→Metal hydroxide+Hydrogen

Specific Reactions

Lithium: $2\text{Li}(s) + 2\text{H}_2\text{O}(l) \rightarrow 2\text{LiOH}(aq) + \text{H}_2(g)$2Li(s)+2H2​O(l)→2LiOH(aq)+H2​(g)

• Floats, fizzes gently, moves around the surface, dissolves slowly.

Sodium: $2\text{Na}(s) + 2\text{H}_2\text{O}(l) \rightarrow 2\text{NaOH}(aq) + \text{H}_2(g)$2Na(s)+2H2​O(l)→2NaOH(aq)+H2​(g)

• Floats, fizzes vigorously, melts into a ball, moves rapidly around the surface.

Potassium: $2\text{K}(s) + 2\text{H}_2\text{O}(l) \rightarrow 2\text{KOH}(aq) + \text{H}_2(g)$2K(s)+2H2​O(l)→2KOH(aq)+H2​(g)

• Floats, fizzes very vigorously, lilac flame (the hydrogen ignites), melts, moves rapidly.

The solutions formed are alkaline (pH above 7) — this is why Group 1 metals are called the alkali metals.

---

Reactivity Trends Down Group 1

graph TD
    A["Going DOWN Group 1"] --> B["Atomic radius INCREASES"]
    B --> C["Outer electron is FURTHER from nucleus"]
    C --> D["More SHIELDING by inner electrons"]
    D --> E["Less attraction between nucleus and outer electron"]
    E --> F["Outer electron lost MORE EASILY"]
    F --> G["Reactivity INCREASES"]

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

Why Reactivity Increases Down the Group

1. Going down Group 1, atoms get larger — more electron shells.
2. The outer electron is further from the nucleus.
3. There is more shielding by inner shells of electrons.
4. The attraction between the nucleus and the outer electron is weaker.
5. The outer electron is lost more easily.
6. Therefore, the element reacts more vigorously.

Exam Tip (AQA 8464): When explaining reactivity trends, you must use the terms "outer electron," "further from the nucleus," "shielding" and "weaker attraction." Simply saying "the atom is bigger" is not sufficient for full marks.

---

Comparison of Reactions with Water

Element	Observation	Vigour
Lithium	Floats, fizzes gently, dissolves slowly	Least vigorous
Sodium	Floats, melts into a ball, fizzes vigorously, moves rapidly	More vigorous
Potassium	Floats, lilac/purple flame, sparks, fizzes very vigorously	Most vigorous (of those commonly tested)

---

Reactions with Non-Metals

Group 1 metals react vigorously with non-metals (such as chlorine) to form ionic compounds:

$2\text{Na}(s) + \text{Cl}_2(g) \rightarrow 2\text{NaCl}(s)$2Na(s)+Cl2​(g)→2NaCl(s)

• The metal atom loses its outer electron → forms a positive ion (Na⁺).
• The non-metal atom gains the electron → forms a negative ion (Cl⁻).

The compounds formed are white solids that dissolve in water to form colourless solutions.

---

Worked Example

Question: Explain why potassium reacts more vigorously with water than sodium. (3 marks)

Answer:

1. Potassium has more electron shells than sodium, so its outer electron is further from the nucleus.
2. There is more shielding from inner electrons.
3. The attraction between the nucleus and the outer electron is weaker, so the outer electron is lost more easily, making potassium more reactive.

---

Common Mistakes

Mistake	Correction
Saying Group 1 metals are hard and dense	They are soft (can be cut with a knife) and have low density
Saying reactivity decreases down the group	Reactivity increases down Group 1
Forgetting that hydrogen gas is produced	The reaction produces metal hydroxide and hydrogen
Not explaining why reactivity increases	You must mention outer electron distance, shielding and weaker attraction
Saying alkali metals react with water to form acids	They form hydroxides (alkalis), which is why they are called alkali metals

---

Summary

• Group 1 metals have one electron in their outer shell and lose it to form 1+ ions.
• They have low melting points, low densities and are soft.
• They react with water to form metal hydroxides (alkalis) and hydrogen gas.
• Reactivity increases down the group because the outer electron is further from the nucleus, there is more shielding, and the electron is lost more easily.
• They are stored under oil to prevent reaction with air and moisture.
• They react vigorously with non-metals to form ionic compounds.

Exam Tip (AQA 8464): Make sure you can write balanced equations for the reactions of Li, Na and K with water. AQA commonly asks for these equations, and you need to include state symbols for full marks.

---

Detailed Observation Table — Reactions with Water