Calcium chloride
4 marks · NormalCalcium chloride is an ionic compound formed from calcium and chlorine atoms.
State the electronic configuration of a calcium atom and a chlorine atom.
Describe, in terms of electron transfer, how calcium and chlorine form ions in calcium chloride.
Draw a dot-and-cross diagram to show the ions present in calcium chloride (CaCl₂). Use dots (•) for calcium’s electrons and crosses (×) for chlorine’s electrons.
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.
Show answer
(a) Ca: 2,8,8,2; Cl: 2,8,7
(b) Each calcium atom loses 2 electrons, one to each chlorine atom. Calcium forms Ca²⁺, and each chlorine forms Cl⁻.
(c) Dot-and-cross diagram showing one Ca²⁺ ion (empty outer shell), two Cl⁻ ions (each with 8 electrons in the outer shell, one of which is a dot from Ca), charges indicated, brackets shown. · must show One Ca²⁺ ion with empty outer shell, Two Cl⁻ ions each with 8 electrons in outer shell, 1 dot and 7 crosses, Charges shown on ions, Square brackets around ions
Common mistakes: Wrong number of outer electrons; Incorrect charge on ions; Both electrons from Ca given to one Cl
Show mark scheme and worked solution
Marking points
A1 (a) · 1 mark · Correct electronic configurations for both calcium (2,8,8,2) and chlorine (2,8,7).
B1 (b) · 1 mark · Correct description of electron transfer: Ca atom loses two electrons, one to each Cl atom.
D1 (c) · 1 mark · Ca²⁺ ion shown with no electrons in outer shell, square brackets, and charge.
D2 (c) · 1 mark · Two Cl⁻ ions shown with 8 outer electrons (7 crosses, 1 dot in each), square brackets and negative charge.
Worked solution
(a) Calcium: 2,8,8,2; Chlorine: 2,8,7.
(b) Calcium loses 2 electrons, giving one to each chlorine atom, forming one Ca²⁺ ion and two Cl⁻ ions.
(c) Draw a central Ca ion (Ca²⁺) with no electrons in the outer shell, in square brackets with 2+ charge. On each side, a Cl⁻ ion in brackets, each with 8 electrons in the outer shell (7 crosses, 1 dot from Ca), with a – charge.