Calcium chloride
3 marks · Normal(a) Calcium chloride is formed when one calcium atom reacts with two chlorine atoms. Calcium transfers electrons to each chlorine atom.
Draw a dot-and-cross diagram to show the formation of calcium chloride. Label each ion and show their charges.
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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Must show: Ca atom with 2 outer electrons (of one symbol, e.g. dots), Each Cl atom with 7 outer electrons (other symbol, e.g. crosses), Shows 2 electrons, one from Ca to each Cl atom, Ions clearly encased in square brackets, Correct charges: Ca2+ ion, 2 Cl- ions shown as superscripts, All electrons shown in the outer shells
Also accept: Dots and crosses may be swapped, but consistent symbol use is required
Common mistakes: Incorrect number of electrons; Missing square brackets; Incorrect charge on ions
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Shows the transfer of one electron from Ca to each Cl atom, forming ions.
A1 · 1 mark · Correct number of electrons drawn around Ca2+ and both Cl- ions using dot-and-cross convention.
A2 · 1 mark · Each ion is labelled with its charge (Ca²⁺, Cl⁻) and surrounded by square brackets.
Worked solution
Draw a dot-and-cross diagram as follows:
- Calcium ion (Ca²⁺): Circle for the Ca ion with (after transfer) no dots or crosses in the outer shell. Place a superscript 2+ charge and surround with square brackets.
- Each chloride ion (Cl⁻): Two circles, each representing a Cl⁻ ion. For each, show 8 electrons (7 crosses and 1 dot in each outer shell if using dot/cross for electron origins). Each is labelled with a superscript negative charge and enclosed in square brackets.
- One electron is transferred from Ca to each Cl atom. Total transferred: two electrons.