1.2.5Atomic Structure and the Periodic Table
Group 1: The Alkali Metals — AQA GCSE Combined Science Trilogy 8464 - Chemistry Revision Notes & Topical Questions
10 min read 7 parts Lesson 16 of 17
Section 1 of 7Group 1: The Alkali Metals
Essential knowledge
Group 1 elements
Group 1 elements the Group 1 metals are known as the alkali metals: lithium, sodium, potassium, rubidium, caesium and francium. They are soft enough to cut with a knife, shiny when freshly cut, and tarnish rapidly in air.
Why 'alkali' metals
Why 'alkali' metals they form alkaline solutions when they react with water, because the product is a soluble metal hydroxide that releases OH− ions. Hydrogen gas is also produced.
Physical properties
Physical properties unlike most metals they have low melting points and low densities; lithium, sodium and potassium float on water. Melting point decreases down the group.
Reactions with water
Reactions with water lithium fizzes steadily; sodium melts into a silvery ball and whizzes around; potassium reacts so vigorously that the hydrogen ignites with a lilac flame. General equation: 2M + 2H2O → 2MOH + H2.
Electronic configuration
Electronic configuration every alkali metal atom has one electron in its outer shell. They react by losing this electron to form an ion with a 1+ charge and the stable configuration of a noble gas, e.g. Na (2.8.1) → Na+ (2.8).
Reactivity trend
Reactivity trend going down the group, atoms have more shells. The outer electron is further from the nucleus and more shielded by inner electrons, so it is less strongly attracted and is lost more easily. Therefore reactivity increases down the group.
Predictions
Predictions rubidium and caesium would react explosively with water, forming RbOH and CsOH. They would be even softer, with lower melting points.
Safety
Safety alkali metals are stored under oil, handled with tongs, used in small pieces and reacted behind a safety screen, wearing goggles.
Reaction with oxygen
Reaction with oxygen freshly cut alkali metals tarnish as they react with oxygen in air, forming a dull oxide layer: 4Na + O2 → 2Na2O. Tarnishing is faster further down the group.
Predicting rubidium
Predicting rubidium it would be a soft metal, shiny when freshly cut but tarnishing very rapidly, with a lower melting point than potassium (below about 63 °C) and a higher density. It would react violently or explosively with water.
Most and least reactive
Most and least reactive lithium, at the top, is the least reactive alkali metal; francium, at the bottom, would be the most reactive.
Hydroxide solutions
Hydroxide solutions the products all have the formula MOH and form colourless solutions with pH above 7, e.g. LiOH, NaOH and KOH.
Section 2 of 7Process & sequence
1
Cut a small piece of the metal (it is stored under oil) with a scalpel and note the shiny surface that quickly tarnishes.
2
Add the piece to a trough of water behind a safety screen.
3
Observe floating, fizzing, melting and any flame.
4
Test the gas with a lighted splint: a squeaky pop shows hydrogen.
5
Add universal indicator to the water: it turns purple (alkaline).
6
Compare the vigour of lithium, sodium and potassium to deduce the reactivity order.
Why reactivity rises down Group 1write these steps in this order; each step is a marking point.
1
More shells down the group
2
Outer electron further from nucleus
3
More shielding by inner shells
4
Weaker attraction on outer electron
5
Electron lost more easily
6
Reactivity increases
Section 3 of 7Compare
| Metal | Observations | Products |
|---|---|---|
| Lithium | Floats, fizzes steadily, slowly gets smaller | LiOH + H2 |
| Sodium | Floats, melts into a ball, fizzes rapidly, moves around | NaOH + H2 |
| Potassium | Melts, moves very quickly, ignites with lilac flame | KOH + H2 |
| Rubidium / caesium (predicted) | Explosive reaction | RbOH / CsOH + H2 |
Universal indicator turns purple as an alkaline hydroxide forms.
| Property | Trend down group | Reason |
|---|---|---|
| Reactivity | Increases | Outer electron lost more easily |
| Atomic radius | Increases | More electron shells |
| Melting point | Decreases | Weaker metallic bonding |
| Density | Generally increases | Mass increases faster than volume |
Section 4 of 7Worked examples
1Write a balanced equation, with state symbols, for lithium reacting with water.
- 2Li(s) + 2H2O(l) → 2LiOH(aq) + H2(g).
2Explain why potassium is more reactive than sodium.
- Potassium (2.8.8.1) has one more shell than sodium (2.8.1).
- Its outer electron is further from the nucleus and more shielded, so the attraction is weaker and the electron is lost more easily.
- Hence potassium reacts faster.
Section 5 of 7Key terms
Section 6 of 7Command terms
Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.
Section 7 of 7Exam technique
Keywords the mark scheme looks for in this lesson
Keywords the mark scheme looks for in this lesson
Alkali metal · Alkali · Metal hydroxide · Electronic configuration · Positive ion · Shielding · Reactivity · Oxidation
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.
How to get full marks (examiner guidance)
How to get full marks (examiner guidance)
Use specification keywords exactly (e.g. electronegativity, nucleophile, dynamic equilibrium, activation energy).
Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.
Avoid vague words
“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.
Do not extrapolate a graph line beyond the data or to zero unless asked.
Six-mark extended responses are marked on content AND a logical, linked line of reasoning.
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