# Group 1 (alkali metals) - lithium, sodium and potassium

> Edexcel International GCSE Chemistry · 4CH1 2017
> Source: https://www.owlsprep.com/study/edexcel-igcse-chemistry-s2-group-1-lithium-sodium-and/

This guide covers core properties, reactions and reactivity trends of Group 1 alkali metals (lithium, sodium, potassium) for Edexcel IGCSE Chemistry, including higher-tier electronic configuration explanations.

**Prerequisites:** [Basic Periodic Table structure and electronic configuration](https://www.owlsprep.com/study/edexcel-igcse-chemistry-s1-periodic-table-electronic-configuration/)

## Learning objectives

- Describe similarities of Li, Na, K reactions with water as evidence of their grouping as a chemical family
- Use differences in reactivity with air and water to identify the trend in reactivity down Group 1
- Predict properties of other Group 1 metals (e.g. rubidium, caesium) using established trends
- Explain the Group 1 reactivity trend using electronic configuration (Higher Tier only)

## Similarities in Group 1 Reactions with Water

**Group 1 Water Reaction** — All Group 1 metals undergo exothermic reaction with water to produce a soluble metal hydroxide and hydrogen gas, forming an alkaline (pH>7) solution.

*Example:* $2Li(s) + 2H_2O(l) \rightarrow 2LiOH(aq) + H_2(g)$

Identical reaction products for lithium, sodium and potassium are key evidence they belong to the same chemical family. The resulting hydroxide solution turns universal indicator blue or purple, confirming its alkalinity.

**Worked example:** Lithium is added to distilled water. Identify the products formed and describe a test to confirm the gaseous product.

1. Step 1: Recall the general Group 1 water reaction: metal + water → metal hydroxide + hydrogen
2. Step 2: Identify products: aqueous lithium hydroxide (LiOH) and hydrogen gas ($H_2$)
3. Step 3: Test for hydrogen: hold a lit splint near the gas, a squeaky pop confirms hydrogen is present.

> **tip**
>
> Always include state symbols in balanced equations for full marks: use (s) for the metal, (l) for water, (aq) for dissolved hydroxide, and (g) for hydrogen.

## Reactivity Trends for Li, Na, K with Air and Water

While all Group 1 metals react similarly with air and water, reaction vigour increases down the group: lithium fizzes gently, sodium reacts vigorously and melts into a silver ball, potassium reacts violently with a lilac flame.

**Group 1 Reactivity Trend** — Reactivity increases as you move down Group 1 of the periodic table, with order of reactivity: potassium > sodium > lithium.

**Worked example:** Equal sized pieces of Li, Na, K are added to identical beakers of water at the same temperature. Rank the metals from least to most vigorous reaction, justifying your answer.

1. Step 1: Recall reactivity increases down Group 1.
2. Step 2: Rank by group position: lithium is highest in the group, followed by sodium, then lowest is potassium.
3. Step 3: Final order (least to most vigorous): Lithium < Sodium < Potassium, as reactivity increases down Group 1.

> **Exam tip:** You may be asked to list observation differences between the three reactions, so memorise key descriptive details for each metal.

## Predicting Properties of Other Group 1 Metals

The consistent reactivity trend down Group 1 allows you to predict properties of less familiar alkali metals like rubidium and caesium, which sit below potassium in the group. You can predict reaction products, reaction vigour and other trend-following properties without memorising specific values for these metals.

**Worked example:** Predict the products formed when rubidium reacts with water, and compare the vigour of its reaction to potassium.

1. Step 1: All Group 1 metals form the same products with water: rubidium hydroxide and hydrogen gas. The balanced equation is shown below:
2. $$2Rb(s) + 2H_2O(l) \rightarrow 2RbOH(aq) + H_2(g)$$
3. Step 2: Rubidium is below potassium in Group 1, so its reactivity is higher.
4. Step 3: Rubidium will react significantly more vigorously than potassium, potentially exploding on contact with water.

> **note**
>
> You will never be asked to recall properties of rubidium or caesium directly: all questions will require you to apply the trend you learned for Li, Na, K to these elements.

## Higher Tier: Reactivity Trend Explanation via Electronic Configuration

**Electronic Configuration Explanation** — All Group 1 elements have 1 electron in their outer shell. Down the group, the outer electron is further from the nucleus, with more inner shells providing shielding, reducing attraction between the nucleus and outer electron, so it is lost more easily, increasing reactivity.

This explanation is strictly qualitative for IGCSE: you do not need to quote ionisation energy values, atomic radius measurements or enthalpy data, only describe the three key factors: distance from nucleus, shielding, and ease of outer electron loss.

**Worked example:** Explain why potassium is more reactive than sodium, in terms of electronic configuration.

1. Step 1: Both sodium and potassium have 1 electron in their outer shell.
2. Step 2: Potassium is lower in Group 1 than sodium, so it has more inner electron shells, meaning its outer electron is further from the nucleus and experiences more shielding from inner shells.
3. Step 3: Attraction between the positive nucleus and negative outer electron is weaker in potassium, so the outer electron is lost more easily, making potassium more reactive than sodium.

> **Exam tip:** Link each factor (distance, shielding) directly to ease of outer electron loss to secure all marks for higher tier explanation questions.

## Common pitfalls

- **Wrong:** Stating reactivity decreases down Group 1
  - Why it fails: Confusing Group 1 trend with Group 7 (halogens) where reactivity decreases down the group
  - Correct: Remember Group 1 reactivity increases down the group, Group 7 reactivity decreases down the group
- **Wrong:** Writing the product of water reaction as metal oxide instead of metal hydroxide
  - Why it fails: Confusing reaction with water with reaction with oxygen in air
  - Correct: Recall the general equation: $2M + 2H_2O \rightarrow 2MOH + H_2$, forming a hydroxide, not oxide
- **Wrong:** Forgetting state symbols in balanced equations
  - Why it fails: Examiners require state symbols for full marks on equation questions
  - Correct: Always add (s) for the metal, (l) for water, (aq) for dissolved hydroxide, (g) for hydrogen
- **Wrong:** Higher tier: Stating the nucleus gets less positive down the group as the reason for easier electron loss
  - Why it fails: Nuclear charge actually increases down the group, but shielding and distance outweigh this effect
  - Correct: Focus on the outer electron being further from the nucleus with more shielding, reducing attraction, making loss easier
- **Wrong:** Predicting rubidium reacts less vigorously than potassium
  - Why it fails: Forgetting the direction of the reactivity trend down Group 1
  - Correct: Elements lower in Group 1 are more reactive, so rubidium reacts more vigorously than potassium

## Cheatsheet

| Metal | Reaction with water observations | Balanced equation | Relative reactivity |
| --- | --- | --- | --- |
| Lithium | Gentle fizzing, moves on surface, no flame | $2Li + 2H_2O(l) → 2LiOH(aq) + H_2(g)$ | Lowest |
| Sodium | Vigorous fizzing, melts to silver ball, may have yellow flame | $2Na + 2H_2O(l) → 2NaOH(aq) + H_2(g)$ | Medium |
| Potassium | Violent reaction, lilac flame, may spit/explode | $2K + 2H_2O(l) → 2KOH(aq) + H_2(g)$ | Highest (of the three) |
| General Group 1 Rule | All form alkaline solution, release hydrogen | $2M + 2H_2O(l) → 2MOH(aq) + H_2(g)$ (M = Group 1 metal) | Increases down group |

## What's next

Now that you have mastered Group 1 alkali metal properties and trends, you are ready to move on to other periodic table groups, starting with Group 7 halogens, which follow the opposite reactivity trend. You will also apply these trend prediction skills to other parts of the periodic table in later inorganic chemistry topics. For higher tier students, make sure you practice writing the electronic configuration explanation for reactivity trends, as this is a common 3-4 mark question in Paper 2C. Don’t forget to link this knowledge to Group 1 flame test identification, which is covered in a separate topic on chemical tests. Past paper practice for this topic will help you get comfortable with describing reaction observations and applying trend rules to unfamiliar Group 1 metals like rubidium and caesium.

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