Calcium chloride
4 marks · NormalCalcium chloride is an ionic compound formed from calcium and chlorine.
State the formula of the calcium ion and the chloride ion.
Draw a dot-and-cross diagram to show how electrons are transferred when calcium reacts with chlorine to form calcium chloride.
Explain why two chlorine atoms are needed for each calcium atom in this compound.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Ca^{2+}, Cl^- · must show Correct charge for Ca ion: 2+, Correct charge for Cl ion: 1-
(b) — · must show Calcium atom loses 2 electrons (shown as dots/crosses), Each electron goes to a separate chlorine atom, Full outer shells for ions, Ions labelled with charges Ca^{2+}, Cl^-
(c) Each chlorine atom can only accept one electron, but calcium loses two electrons, so two chlorine atoms are needed. · must show Refers to calcium losing two electrons, Each chlorine accepting one electron
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Marking points
B1 (a) · 1 mark · States Ca^{2+} and Cl^- as the ions.
D1 (b) · 1 mark · Diagram shows correct loss of 2 electrons from calcium and transfer of 1 to each chlorine.
D2 (b) · 1 mark · Ions labelled Ca^{2+} and Cl^- with full outer shells (dot-and-cross diagram logic correct).
E1 (c) · 1 mark · Explains that two chlorine atoms are needed because calcium loses 2 electrons, one to each chlorine.
Worked solution
a) The formulae: Ca^{2+} and Cl^-
b) Diagram:
c) Calcium loses two electrons, but each chlorine needs only one electron, so two chlorine atoms are needed to accept both electrons.