Chemistry of the Elements

Group 1 — Alkali Metals: Comprehensive Revision Notes

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Key Definitions and Terminology

**Alkali metals**: The elements in Group 1 of the periodic table — lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr). They are called "alkali" metals because they react with water to form alkaline solutions.
**Relative reactivity**: The comparison of how vigorously elements in a group react, which in Group 1 increases going **down** the group.
**Alkaline solution**: A solution with a pH greater than 7; formed when Group 1 metals react with water, producing a metal hydroxide.
**Metal hydroxide**: The ionic compound produced when a Group 1 metal reacts with water (e.g., NaOH — sodium hydroxide).
**Electron configuration**: The arrangement of electrons in shells around the nucleus. All Group 1 elements have **one electron** in their outermost shell.
**Oxidation**: The loss of electrons. When Group 1 metals react, each atom loses its single outer electron to form a **+1 ion** (e.g., Na → Na⁺ + e⁻).

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Physical Properties of Group 1 Metals

Group 1 metals are **soft** — they can be cut with a knife, exposing a shiny surface that quickly tarnishes in air.
They have **low densities** compared with other metals. Lithium, sodium, and potassium are all **less dense than water** (lithium is the least dense metal).
They have **relatively low melting and boiling points** for metals, and these **decrease** going down the group.
They are shiny when freshly cut but rapidly oxidise in air, so they are stored under **oil** to prevent reaction with oxygen and moisture.

| Property | Trend down Group 1 |

|---|---|

| Melting point | Decreases |

| Density | Generally increases (with some irregularity) |

| Reactivity | Increases |

| Atomic radius | Increases |

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Main Concepts

1. Electronic Structure Explains Group Behaviour

Every Group 1 element has **one electron in its outer shell**.
This single outer electron is easily lost during reactions, forming a **+1 ion** (e.g., K → K⁺ + e⁻).
Because they all have the same number of outer-shell electrons, they all react in a **similar way** — this is why they are in the same group.

2. Why Reactivity Increases Down the Group

Going down Group 1, each successive element has **more electron shells**.
The outer electron is **further from the nucleus** and is **shielded** by more inner electron shells.
This means the outer electron experiences a **weaker attraction** (effective nuclear charge) from the nucleus.
Therefore, the outer electron is **lost more easily**, making the atom more reactive.
**Summary**: Li < Na < K < Rb < Cs in order of increasing reactivity.

3. Reaction with Water

All Group 1 metals react 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 = any Group 1 metal)*
The resulting solution is **alkaline** (pH > 7), which can be confirmed using **universal indicator** (turns blue/purple) or **litmus** (turns blue).
The hydrogen gas produced can be tested with a **burning splint** — it burns with a **squeaky pop**.

#### Observations for specific metals:

| Metal | Observations |

|---|---|

| Lithium | Floats, fizzes steadily, moves slowly on the surface, dissolves gradually |

| Sodium | Floats, fizzes vigorously, melts into a silvery ball, moves rapidly on the surface, dissolves faster than lithium |

| Potassium | Floats, fizzes very vigorously, melts into a ball, lilac/purple flame produced (ignites the hydrogen), moves very rapidly, may spit |

4. Reaction with Oxygen (Burning in Air)

Group 1 metals burn in oxygen/air to form **metal oxides**.
**General equation**: 4M(s) + O₂(g) → 2M₂O(s)
Characteristic **flame colours** are observed:
Lithium → **red** flame
Sodium → **yellow/orange** flame
Potassium → **lilac** flame

5. Reaction with Chlorine

Group 1 metals react vigorously with chlorine gas to form white **metal chlorides** (ionic compounds).
**General equation**: 2M(s) + Cl₂(g) → 2MCl(s)
For example: 2Na(s) + Cl₂(g) → 2NaCl(s)

6. Predicting Properties of Unfamiliar Group 1 Elements

You may be asked about rubidium or caesium. Use the **trends** to predict:
Rubidium would react **more vigorously** with water than potassium.
Caesium would react **even more vigorously** — explosively with water.
Their melting points would be **lower** than potassium's.

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Worked Examples and Real-World Applications

Worked Example 1: Writing a Balanced Equation

Question: Write a balanced symbol equation for the reaction of potassium with water.

Solution:

Identify reactants: K and H₂O
Identify products: KOH and H₂
Unbalanced: K(s) + H₂O(l) → KOH(aq) + H₂(g)
Balance: **2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g)**
Include state symbols: solids (s), liquid (l), aqueous (aq), gas (g) ✓

Worked Example 2: Using Trends to Make Predictions

Question: Rubidium is below potassium in Group 1. Predict what would be observed when rubidium is added to water.

Answer:

Rubidium would float on the water (low density).
It would react **more vigorously/violently than potassium**.
It would melt into a ball due to the heat of the reaction (lower melting point than K).
It would **ignite immediately** and may explode.
The metal would dissolve rapidly, producing hydrogen gas (squeaky pop) and an alkaline solution of rubidium hydroxide, RbOH.
**Explanation**: Rubidium has more electron shells than potassium, so its outer electron is further from the nucleus, more shielded, and more easily lost — making it more reactive.

Real-World Application: Sodium and Street Lighting

Sodium is used in some types of **street lamps** (low-pressure sodium lamps), which emit the characteristic **yellow-orange light** associated with sodium's emission spectrum.
Lithium compounds are used in **rechargeable batteries** (lithium-ion batteries) found in smartphones and electric vehicles, taking advantage of lithium's low density and high reactivity.
The vigorous reactivity of Group 1 metals with water is why they must be stored carefully under oil in laboratories — a practical safety consideration students should understand.

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Exam Technique Tips for Edexcel IGCSE

Tip 1: "Explain why reactivity increases" questions (3–4 marks)

Edexcel mark schemes require a logical chain of reasoning. Always include all four of these linked points:

More electron shells / outer electron is further from the nucleus
Greater **shielding** effect from inner electrons
Weaker attraction between the nucleus and the outer electron
Outer electron is lost more easily

> ⚠️ Simply writing "the atom is bigger" is not enough for full marks. You must explicitly connect distance/shielding → weaker attraction → easier electron loss.

Tip 2: Observation vs Explanation — Know the Difference

When a question says **"describe what you would observe"**, give only things you can **see, hear, or measure** (e.g., "fizzing," "floats," "melts into a ball," "lilac flame," "metal dissolves/gets smaller").
Do **NOT** write about atoms, electrons, or equations in an observation answer — these are **explanations**, not observations.
When a question says **"explain"**, then you should refer to electron structure and bonding.
Edexcel examiners will **not award marks** for explanations given in place of observations (and vice versa). Read the command word carefully.

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Quick Summary Checklist

[ ] Group 1 metals have **1 outer electron** → form **+1 ions**
[ ] Reactivity **increases** down the group (outer electron easier to lose)
[ ] Melting points **decrease** down the group
[ ] React with water → **metal hydroxide + hydrogen**
[ ] React with oxygen → **metal oxide**; react with chlorine → **metal chloride**
[ ] Stored under **oil** to prevent reaction with air and water
[ ] Solutions formed are **alkaline** (pH > 7)
[ ] Know observations for Li, Na, and K with water in detail

Subtopics

Revision Method

Group 1 — Alkali Metals