Group 1 Alkali Metals

Summary: Group 1 metals (Li, Na, K, Rb, Cs) are soft, reactive metals with low density. Reactivity increases down the group. They react vigorously with water forming alkaline hydroxides and hydrogen gas. Tags: igcse chemistry periodic-table Created: 2026-07-14 Last Updated: 2026-07-16

Physical Properties

Group 1 metals are soft, have low density, and have low melting and boiling points compared to most other metals.

Trends down the group (Li to Cs):

Key data for the first three alkali metals (IGCSE focus):

All Group 1 metals are shiny when freshly cut, but they tarnish rapidly in air as they react with oxygen to form an oxide layer. They are good conductors of heat and electricity (due to delocalised electrons in metallic bonding).

Electronic Structure

All Group 1 metals have 1 electron in their outer shell:

Why they form 1+ ions: Each alkali metal atom loses its single outer electron to achieve a stable noble gas electron configuration. For example, Na (2.8.1) loses 1 electron → Na+ (2.8), which is the same as neon. Losing 1 electron is much easier than gaining 7 to fill the outer shell.

The ion formed therefore has a 1+ charge: Li → Li+ + e-, Na → Na+ + e-, K → K+ + e-.

Chemical Properties and Reactivity

Alkali metals are very reactive and must be stored under oil to prevent contact with air and water.

Reactivity INCREASES down the group (K is more reactive than Na, which is more reactive than Li). This is the opposite trend to the halogens.

Why reactivity increases down Group 1:

1. As you go down the group, the outer electron is in a shell further from the nucleus.
2. There are more inner electron shells, which provide shielding — they block the attractive force of the nucleus on the outer electron.
3. The nuclear attraction on the outer electron is therefore weaker.
4. Less energy is needed to remove the outer electron, so the atom loses its outer electron more easily.
5. Easier electron loss = more reactive.

Example: Potassium has its outer electron in the 4th shell, while sodium’s is in the 3rd shell. The outer electron in potassium is further from the nucleus and experiences more shielding from inner electron shells. Therefore, the nuclear attraction on the outer electron is weaker, so potassium loses its outer electron more easily.

Reactions with Water

All alkali metals react vigorously with water to form a metal hydroxide (an alkali — hence the group name) and hydrogen gas.

General equation: 2M(s) + 2H2O(l) → 2MOH(aq) + H2(g)

Specific equations for IGCSE:

• 2Li(s) + 2H2O(l) → 2LiOH(aq) + H2(g)
• 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
• 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)

Observations for each metal with water:

For rubidium and caesium (Rb and Cs), the reaction is explosive — these are not usually demonstrated in schools.

Testing the products:

• The solution turns universal indicator purple → confirms the presence of an alkali (OH- ions).
• The gas produced gives a squeaky pop with a lighted splint → confirms hydrogen gas (H2).

Reactions with Oxygen

Alkali metals react with oxygen when heated (and tarnish slowly at room temperature).

General equation: 4M(s) + O2(g) → 2M2O(s)

• 4Li(s) + O2(g) → 2Li2O(s) (lithium oxide — white)
• 4Na(s) + O2(g) → 2Na2O(s) (sodium oxide — white; but sodium can also form the peroxide Na2O2 when burned in excess oxygen)
• 4K(s) + O2(g) → 2K2O(s) (potassium oxide)

Flame colours when burning in oxygen/air:

• Lithium (Li): red flame
• Sodium (Na): yellow / golden-yellow flame
• Potassium (K): lilac flame (pale purple)

Reactions with Halogens

Alkali metals react vigorously with halogens (Group 7) to form metal halides (ionic compounds).

General equation: 2M + X2 → 2MX (where X = halogen)

• 2Na(s) + Cl2(g) → 2NaCl(s) — vigorous reaction, white solid formed
• 2K(s) + Br2(l) → 2KBr(s)
• 2Li(s) + I2(s) → 2LiI(s)

These are redox reactions: the alkali metal is oxidised (loses electrons: M → M+ + e-), and the halogen is reduced (gains electrons: X2 + 2e- → 2X-).

Flame Tests

Flame tests are used to identify metal ions (cations) in compounds. For Group 1:

Method (IGCSE standard):

1. Clean a nichrome or platinum wire by dipping in concentrated HCl and heating in a blue Bunsen flame until no colour is imparted.
2. Dip the clean wire into the sample (solid or solution).
3. Hold the wire in the hottest part of the flame (the edge of the blue cone) and observe the colour.

Storage

Alkali metals are stored under oil (e.g., paraffin oil or mineral oil) to prevent them from reacting with:

• Oxygen in the air (which would form metal oxides — they tarnish)
• Water vapour in the air (which would cause a reaction producing hydrogen gas and the metal hydroxide)

Lithium is less dense than oil and tends to float — it may be stored under a hydrocarbon solvent or coated in wax instead.

Uses

Key Points

• Group 1 = alkali metals: Li, Na, K, Rb, Cs (IGCSE focuses on Li, Na, K)
• All have 1 electron in their outer shell → form 1+ ions
• Soft, low density, low mp/bp; shiny when freshly cut but tarnish quickly
• Reactivity increases down the group (K > Na > Li)
• Reaction with water: metal + water → metal hydroxide + hydrogen
• Reaction with oxygen: metal + oxygen → metal oxide (4M + O2 → 2M2O)
• Reaction with halogens: metal + halogen → metal halide (2M + X2 → 2MX)
• Flame test colours: Li = red, Na = yellow/orange, K = lilac
• Stored under oil to prevent reaction with air and water
• The solution formed with water is alkaline (metal hydroxide) — universal indicator turns blue/purple

Key Concepts from Past Papers

• Reactivity increases down Group 1 because outer electron is further from nucleus with more shielding
• 2Na + 2H2O → 2NaOH + H2

Keywords from Past Papers

sodium, chloride, lithium, bromine, potassium, water, values, bromide, iodide, chlorine, point, between, inclusive, these, melting

Related Notes

• Periodic Table Trends
• Group 7 Halogens
• Group 0 Noble Gases
• Transition Metals
• Atomic Structure

Sources

• OpenStax Chemistry 2e — Chapter 6: Electronic Structure and Periodic Properties, Rice University (free, CC BY 4.0)
• BBC Bitesize GCSE Chemistry — Group 1 Alkali Metals, BBC (free educational resource)
• Cambridge IGCSE Chemistry 0620 — Syllabus topic 8 (The Periodic Table), Cambridge Assessment International Education
• CK-12 Chemistry for High School — Alkali Metals, CK-12 Foundation (free, CC BY-NC 3.0)

Past Paper Sources

• 0620/31 May/June 2015: Q66(b)(ii) (0m)
• 0620/32 Feb/March 2017: Q11(a)(ii) (1m), Q11(a)(vi) (1m), Q11(a)(ii) (1m) (+1 more)
• 0620/32 Feb/March 2018: Q11(a)(ii) (1m), Q11(a)(v) (1m), Q22(a)(ii) (1m) (+1 more)
• 0620/32 Feb/March 2020: Q66(b)(i) (3m), Q55(d)(i) (2m)
• 0620/32 Feb/March 2021: Q22(a)(iv) (1m), Q77(b)(iii) (1m), Q77(e)(i) (0m) (+2 more)
• 0620/32 Feb/March 2023: Q88(c)(i) (2m)
• 0620/32 May/June 2020: Q55(c)(i) (1m)
• 0620/33 May/June 2019: Q44(c)(i) (2m), Q11(a)(v) (1m), Q33(a)(ii) (1m)
• 0620/33 May/June 2022: Q33(c)(i) (2m)
• 0620/33 May/June 2023: Q22(b)(i) (2m)
• 0620/33 October/November 2016: Q11(a)(ii) (1m), Q66(c)(iii) (0m), Q11(a)(ii) (1m)
• 0620/33 October/November 2024: Q55(b)(i) (0m)

Common Misconceptions