Group 1 — the alkali metals

Group 1 (left-hand column) is lithium, sodium, potassium, rubidium, caesium, francium. They each have one outer electron, which they readily lose to form a 1+ ion.

General properties

• Soft (cut with a knife).
• Low density (Li, Na, K float on water).
• Shiny when freshly cut, tarnish quickly in air (oxidise).
• Low melting points compared to most metals.
• Stored under oil to keep them away from oxygen and water.

Reaction with water

All Group 1 metals react with water to form an alkaline hydroxide and hydrogen gas.

General equation: 2 M + 2 H_2 O -> 2 M(OH) + H_2

Metal	Observation
Lithium	Floats, fizzes steadily, gradually disappears
Sodium	Floats, melts into a ball, fizzes vigorously, may catch fire (yellow flame)
Potassium	Floats, melts, ignites instantly with a lilac flame, sometimes spits

The hydroxide solution turns universal indicator purple (alkaline).

Trends going down the group

• Reactivity increases down the group.
• Melting point decreases down the group.
• Atomic radius increases down the group.

Why does reactivity increase?

Each successive Group 1 atom has an extra full shell of electrons, so the outer electron is:

• Further from the nucleus.
• Shielded by more inner electrons.

Both effects weaken the attraction on the outer electron, so it is lost more easily, and the metal is more reactive.

WJEC exam tip

For "explain the trend in reactivity down Group 1", the three magic words are: distance, shielding, attraction. "Outer electron is further from the nucleus and shielded by more electrons, so the attraction is weaker and it is lost more easily." Memorise this sentence — it works for OCR/AQA/Edexcel/WJEC alike.