Group 1 — the alkali metals

Group 1 contains lithium, sodium, potassium, rubidium, caesium and francium. These alkali metals sit on the far left of the periodic table and share a striking set of properties — and a striking trend in reactivity.

Electronic structure

Each alkali metal has one electron in its outer shell:

• Li: 2,1
• Na: 2,8,1
• K: 2,8,8,1

This single outer electron is easily lost to form a +1 ion (Li⁺, Na⁺, K⁺, etc.) with a full outer shell. This explains all of Group 1's chemistry.

Physical properties

• Soft — can be cut with a knife (Li hard, getting softer down the group).
• Low density — Li, Na, K float on water.
• Shiny when freshly cut — but rapidly tarnish in air (oxide layer).
• Low melting points for metals (compared with iron, copper, etc.).

Stored under oil to keep them away from air and moisture.

Reactions of alkali metals

With water (the famous demo)

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

Products: alkali hydroxide + hydrogen gas. The water gradually becomes alkaline (turns universal indicator purple).

Observations show increasing reactivity down the group:

• Lithium: floats, fizzes gently, dissolves slowly.
• Sodium: floats, fizzes vigorously, melts into a silver ball that whizzes about, may produce a spark.
• Potassium: catches fire with a lilac flame, hydrogen ignites; sometimes explodes.
• Rubidium and caesium: extremely violent (sometimes explosive), often demonstrated only on video.

With oxygen

4Na(s) + O₂(g) → 2Na₂O(s) Burns brightly to form a basic metal oxide. Reactivity again increases down the group.

With chlorine

2Na(s) + Cl₂(g) → 2NaCl(s) White ionic salt — same trend.

Reactivity trend explained

Reactivity increases down Group 1. Reason:

1. The outer electron is in a shell further from the nucleus.
2. Inner electron shells shield the outer electron from the positive nucleus.
3. So the attraction holding the outer electron is weaker.
4. The outer electron is lost more easily, so the metal is more reactive.

(This is the textbook 3-mark explanation; learn it word-for-word.)

Compounds of alkali metals

All Group 1 ions are colourless, so most Group 1 compounds are white solids that dissolve in water to form colourless, alkaline solutions:

• Sodium hydroxide (NaOH) — strong alkali used in soap, paper, cleaning.
• Potassium chloride (KCl) — salt substitute, fertiliser.

A flame test (C8.4) gives Group 1 ions characteristic colours: Li (red), Na (orange), K (lilac).

Links

Builds on C1.4 (electronic structure → reactivity). Compare with C1.6 (unreactive Group 0) and C1.8 (Group 7, where reactivity decreases down). Reactivity series in C4 uses the same logic.