GCSE Chemistry · The periodic table

Group 1: the alkali metals

Lithium, sodium and potassium all react with water, but each one more violently than the last. Drop each metal into water and watch what happens, then find out why reactivity increases down the group.

GCSE ChemistryCombined Science
Part 1

Reacting with water

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What you see: lithium

    Your results

    MetalTime to reactObservations

    Times are simulated for pieces of the same size. Real pieces are cut to about the size of a grain of rice. Your teacher does this demonstration behind a safety screen, using tweezers and wearing goggles.

    Part 2

    Why does reactivity increase down the group?

    When a group 1 metal reacts, each atom loses its one outer electron. The easier that electron is to lose, the more reactive the metal.

    The dashed line shows the attraction between the nucleus and the outer electron. Thicker means stronger.
    1One outer electronEvery group 1 atom has one electron in its outer shell. It reacts by losing it to form a 1+ ion: Na → Na⁺ + e⁻
    2More shellsGoing down the group, atoms have more shells. The outer electron is further from the nucleus.
    3Weaker attractionThe further away it is, the weaker the attraction between the outer electron and the positive nucleus. Inner shells also shield it.
    4Lost more easilySo the outer electron is lost more easily, and the metal reacts more vigorously.

    Potassium's nucleus has more protons (+19) than sodium's (+11), but its outer electron is so much further away and so well shielded that it is still held less strongly.

    Physical properties

    Trends down the group

    Melting point (°C)

    MetalElectronic structureMelting point / °CDensity / g/cm³

    Properties of the alkali metals

    • Soft: they can be cut with a knife, and get softer down the group.
    • Shiny when freshly cut: they quickly go dull (tarnish) as they react with oxygen in the air.
    • Low density: lithium, sodium and potassium float on water.
    • Low melting points for metals, decreasing down the group.
    • Stored under oil to stop them reacting with oxygen and water vapour in the air.
    • They form white ionic compounds that dissolve in water to give colourless solutions.

    Other reactions

    With oxygen: metal oxide (tarnishing) 4Na + O₂ → 2Na₂O With chlorine: white metal chloride 2Na + Cl₂ → 2NaCl With water: metal hydroxide + hydrogen 2Na + 2H₂O → 2NaOH + H₂

    All three reactions get more vigorous down the group.

    Check understanding

    Quick quiz

    Longer answers

    Exam-style questions: 10 questions

    They start easy and get harder. Write your answer first, then check it.