A-LevelChemistryChemical bonding9701/22 · May/June 2023 · Q112 Marks

The melting points of some solids are shown in Table 1.1. Table 1.1 solid | melting point/K ---|--- magnesium | 923 phosphorus | 317 sodium chloride | 1074 sulfur | 392

(a)(i)State the type of bonding present in magnesium and in sodium chloride. bonding in magnesium bonding in sodium chloride[1]
(a)(ii)Explain the difference in the melting points of magnesium and sodium chloride.[1]
(a)(iii)Explain the difference in the melting points of phosphorus and sulfur in terms of structure and bonding.[2]
(b)(i)Define electronegativity.[1]
(b)(ii)Explain why electronegativity increases across a period.[2]
(b)(iii)Name the strongest intermolecular force that exists between NH3(l) molecules.[1]
(b)(iv)Draw a diagram to show the formation of the strongest intermolecular force between two molecules of NH3(l). Include any relevant lone pairs of electrons and dipoles.[2]
(b)(v)The melting points of ice and ammonia are shown in Table 1.2. Table 1.2 solid | melting point/K ---|--- ice | 273 ammonia | 195 Suggest two reasons for the difference in the melting points of ice and ammonia.[2]

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

[1] bonding in magnesium – metallic AND bonding in sodium chloride – ionic
[1] bonds in NaCl are stronger than bonds in Mg
[2] M1 S8/molecules of sulfur have more electrons (than P4/ molecules of phosphorus) M2 S has stronger instantaneous dipole-induced dipole forces (than phosphorus / P)
[1] power of an atom to attract electrons to itself
[2] (across a period) • increase in nuclear charge • similar shielding • (so) increase in nuclear attraction for bonding / outer / valence electrons OR bonding / outer / valence electron(s) are more strongly attracted to nucleus Two correct for one mark, three correct for two marks
[1] hydrogen bond
[2] M1 link shown as a dashed line between the lone pair of electrons from N of one NH3 to one H on other NH3 M2 minimum 3 correct partial charges (on adjacent atoms) over two NH3 molecules EITHER δ-N—δ+H - - - δ-N OR δ+H - - -δ-N-δ+H
[2] M1 O is more electronegative than N M2 two H-bonds per water molecule : 1 per ammonia molecule.

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