A-LevelChemistryChemical bonding9701/22 · Oct/Nov 2017 · Q110 Marks
The elements sodium to sulfur react with chlorine. The melting points of some of the chlorides formed are shown. chloride | NaCl | MgCl2 | AlCl3 | SiCl4 | PCl3 | SCl2 melting point/K | 1074 | 987 | 463 | 203 | 161 | 195
- (a)Predict the shapes of AlCl3 and PCl3. Draw diagrams to show the shapes, name the shapes and state the bond angles.[4]
- (b)(i)Explain, in terms of structure and bonding, why the melting point of SiCl4 is much lower than that of NaCl.[3]
- (b)(ii)Explain why the melting point of SiCl4 is higher than that of PCl3.[2]
- (iii)Draw the 'dot-and-cross' diagram of a molecule of SiCl4. Show outer electrons only.[1]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.
- AlCl3 diagram: Al in center, 3 Cl atoms attached, no lone pairs on Al.
- AlCl3 shape: trigonal planar
- AlCl3 angle: 120°
- PCl3 diagram: P in center, 3 Cl atoms attached, 1 lone pair on P.
- PCl3 shape: (trigonal) pyramid(al)
- PCl3 angle: 100–107°
- [1] SiCl4 simple / molecular AND Van der Waals' / id-id forces / London / dispersion forces / IMFs
- [1] NaCl ionic OR giant
- [1] bonding (in NaCl) stronger (than forces in SiCl4) owtte
- [1] SiCl4 has more electrons ORA
- [1] stronger Van der Waals' / id-id forces / London / dispersion forces / IMFs
- [1] Dot-and-cross diagram of SiCl4 showing central Si bonded to four Cl atoms. Each Cl has 3 lone pairs and shares one pair with Si. Si has no lone pairs. All outer electrons shown.
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