Elements of the side subgroup of group II
Zn, Cd and Hg are in the side subgroup of group II; their outer shell has 2 s-electrons, they mostly show the oxidation state +2 in compounds, and the reducing power falls from zinc to mercury. The zinc ore is zinc blende ZnS: it is roasted and then reduced with coal or CO: 2ZnS + 3O₂ → 2ZnO + 2SO₂ and ZnO + C → Zn + CO. Zinc stands before hydrogen in the activity series: Zn + 2HCl → ZnCl₂ + H₂↑, and it is also amphoteric: Zn + 2NaOH + 2H₂O → Na₂[Zn(OH)₄] + H₂↑. ZnO and Zn(OH)₂ are amphoteric too: ZnO + H₂SO₄ → ZnSO₄ + H₂O; ZnO + 2NaOH + H₂O → Na₂[Zn(OH)₄]. We obtain Zn(OH)₂ from a Zn²⁺ salt with alkali: ZnSO₄ + 2NaOH → Zn(OH)₂↓ + Na₂SO₄. Zinc is used as a coating to protect iron from corrosion (galvanised sheet), in galvanic cells and in alloys (brass); ZnSO₄·7H₂O is zinc vitriol, a zinc micro-fertiliser. Mercury (Hg) is a liquid metal at ordinary conditions; its vapour and compounds are extremely poisonous, so if a mercury instrument breaks, tell an adult and the teacher at once and do not touch the mercury. Solutions of metals in mercury are called amalgams.
Table: for Zn, Cd and Hg give period number, Z, outer electrons, state of the simple substance, toxicity. Discuss with adults what to do if a mercury thermometer breaks: never collect it by hand or with a vacuum cleaner.