What is a covalent bond?
4 marks · NormalDraw a dot-and-cross diagram to show the covalent bonding in a molecule of ammonia (NH).
State the number of bonding pairs and lone pairs of electrons on the nitrogen atom in ammonia.
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) Correct dot-and-cross diagram for NH3 showing three N–H bonds (each as a shared pair, dots for N, crosses for H or vice versa), and a lone pair on N. · must show N with 3 H bonded with shared electron pairs (dot+cross for each bond), 1 lone pair on N
(b) Nitrogen atom has 3 bonding pairs and 1 lone pair.
Must show: NH3 diagram: N in centre, 3 H atoms, 3 bonding pairs (dot+cross), 1 lone pair on N
Also accept: Electrons as dots/crosses or any two distinct symbols.; Pairs together or separated as long as total count is correct.
Common mistakes: Incorrect number of electrons shown.; Missing lone pair.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · All atoms (N, 3 H) placed correctly, valence electrons shown using dot-and-cross notation.
B2 (a) · 1 mark · Three bonding pairs (shared pairs between N and H) AND one lone pair correctly shown on N.
B3 (b) · 1 mark · Correctly states ammonia has 3 bonding pairs.
B4 (b) · 1 mark · Correctly states ammonia has 1 lone pair on nitrogen.
Worked solution
b) Ammonia has 3 bonding pairs and 1 lone pair of electrons on the nitrogen atom.