ZIMSEC O Level · Chemistry · Form 3
Elements are arranged by proton number. Elements in a group have the same number of outer electrons and similar properties.
Group I (alkali metals: Li, Na, K)
Soft, low density, stored under oil. React with water to form an alkaline hydroxide and hydrogen: 2Na + 2H₂O → 2NaOH + H₂. Reactivity increases down the group because the outer electron is further from the nucleus and lost more easily.
Group VII (halogens: F, Cl, Br, I)
Diatomic non-metals; colour darkens down the group (chlorine pale green gas, bromine red-brown liquid, iodine dark grey solid). Reactivity decreases down the group. A more reactive halogen displaces a less reactive one: Cl₂ + 2KBr → 2KCl + Br₂.
Group 0 (noble gases)
Full outer shells, so unreactive. Uses: argon in light bulbs, helium in balloons, neon in signs.
Transition metals
Iron, copper, nickel: high melting points, coloured compounds, often used as catalysts (iron in the Haber process).
Across a period
Metals on the left change to non-metals on the right.
Check yourself
- Why is potassium more reactive than sodium?
- Predict the state of astatine (below iodine) at room temperature.
- Give one use of argon.
Show answers
- Its outer electron is further from the nucleus, so it is lost more easily.
- Solid (and black).
- Filling light bulbs (an inert atmosphere for welding is also acceptable).
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