Covalent Bonding
5 marks · EasyDraw a dot-and-cross diagram to show the covalent bonding in a molecule of ammonia (NH).
Explain why ammonia is a gas at room temperature, using your understanding of intermolecular forces.
State how many lone pairs of electrons are present on the nitrogen atom in the ammonia molecule.
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) Diagram showing N atom in centre, three shared pairs (one dot and one cross) to each of three H atoms, and one lone pair of electrons on N. · must show One lone pair on nitrogen, Three single bonds to three hydrogens
(b) Ammonia has a simple molecular structure with weak intermolecular forces, so not much energy is required to overcome them. Therefore, ammonia is a gas at room temperature.
(c) 1
Must show: Central N atom with three covalent bonds to H atoms; correct lone pair
Also accept: Any correct diagram with three single bonds, correct lone pair
Common mistakes: Missing lone pair on N; Incorrect number of bonds
Show mark scheme and worked solution
Marking points
D1 (a) · 1 mark · Correct dot-and-cross diagram: N in centre, 3 single bonds to H atoms (with each bond as a shared dot and cross).
A1 (a) · 1 mark · One lone pair on N atom represented correctly.
M1 (b) · 1 mark · Mentions weak intermolecular forces in ammonia.
A2 (b) · 1 mark · Links weak intermolecular forces to low energy required for boiling; explains gaseous state at room temp.
B1 (c) · 1 mark · States '1' as the number of lone pairs on nitrogen atom.
Worked solution
a) Ammonia (NH3) dot-and-cross diagram:
b) Ammonia is a gas at room temperature because its molecules are held together by weak intermolecular forces, so only a small amount of energy is needed for the molecules to escape to the gas phase.
c) Nitrogen in ammonia has 1 lone pair of electrons.