Calcium nitride has the formula

CHEMISTRY · Single correct · AP · Chemistry · Atomic Structure and Properties · Atomic Structure and Properties

Problem

Calcium nitride has the formula Ca3N2\mathrm{Ca_{3}N_{2}}. Which of the following statements best explains why this particular ratio of ions is observed? (a) Because nitrogen’s high electronegativity draws in additional calcium ions until lattice energy is minimized, the compound stabilizes at a 3∶2 ratio, Ca3N2\mathrm{Ca_{3}N_{2}}. (b) Calcium typically forms +3+3 ions and nitrogen −2-2 ions, so three Ca3+\mathrm{Ca^{3+}} ions balance two N2−\mathrm{N^{2-}} ions, yielding Ca3N2\mathrm{Ca_{3}N_{2}}. (c) Ca2+\mathrm{Ca^{2+}} and N3−\mathrm{N^{3-}} ions combine in the smallest whole-number ratio that gives overall electrical neutrality; three calcium ions provide +6+6 charge and two nitride ions provide −6-6 charge, so the empirical formula is Ca3N2\mathrm{Ca_{3}N_{2}}. (d) Each calcium atom donates three electrons from its 4s and 3d orbitals to a single nitrogen atom, requiring three calcium atoms for every two nitrogens and producing Ca3N2\mathrm{Ca_{3}N_{2}}.

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