O-LevelChemistryAtomic Structure5070/22 · May/June 2015 · Q312 Marks

Two isotopes of phosphorus are 31P and 32P.

(a)State one difference and one similarity between these two isotopes.[2]
(b)Phosphorus forms simple molecules which have a relative molecular mass of 124. Suggest the formula of a phosphorus molecule.[1]
(c)(i)Phosphorus has a low melting point and does not conduct electricity. Explain why phosphorus has a low melting point.[1]
(c)(ii)Explain why phosphorus does not conduct electricity.[1]
(d)Complete the table for 31P3-. number of neutrons number of protons electronic configuration[3]
(e)Phosphorus forms a compound called phosphine, PH3. Draw the 'dot-and-cross' diagram to show the bonding in a molecule of phosphine. Only draw the outer shell electrons.[2]
(f)Phosphine ignites in air to make water and phosphorus(V) oxide. Construct the equation for this reaction.[2]

Mark scheme

Marking points from the official mark scheme (May/June 2015). The mark or mark type is shown in brackets.

[2] (a) (Different) number of neutrons/(different) mass number/(different) nucleon number/phosphorus 32 has one extra neutron/atomic mass/mass (1)
(Same) number of protons/(same) atomic number/both have 15 protons (1)
[1] (b) P4 (1)
[1] (c) (i) Weak intermolecular forces/weak attraction between molecules (1)
[1] (ii) No free electrons/no delocalised electrons/all electrons used in bonding/no mobile electrons(1)
[3] (d) number of neutrons: 16 (1)
number of protons: 15 (1)
electronic configuration: 2,8,8 (1)
[2] (e) All three shared pairs between H and P (1)
Rest of structure correct (1)
[2] (f) 2PH3 + 4O2 → P2O5 + 3H2O
Correct formulae (1)
Balancing - dependent on correct formulae (1)

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