Formulae for ionic compounds
3 marks · EasyThe ions formed by magnesium and sulfur combine to make an ionic compound.
State the symbol and charge of the ion formed by magnesium.
State the symbol and charge of the ion formed by sulfur.
Write the formula for the ionic compound formed from these ions.
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(a) Mg$^{2+}$
(b) S$^{2-}$
(c) MgS
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Marking points
B1 (a) · 1 mark · Correct symbol and charge for magnesium ion: Mg$^{2+}$
B2 (b) · 1 mark · Correct symbol and charge for sulfur ion: S$^{2-}$
B3 (c) · 1 mark · Correct formula: MgS (follow-through)
Worked solution
a) Magnesium (Group 2) forms Mg$^{2+}$.
b) Sulfur (Group 6) forms S$^{2-}$.
c) 2+ and 2– charges balance 1:1, so the formula is MgS.