PeriodicityEdexcel A-Level Chemistry: Subtopic test

1. 1
   The melting temperatures of the Period 3 elements, in °C, are: Na 98, Mg 650, Al 660, Si 1410, P 44, S 115, Cl −101 and Ar −189.

   (a)

   Which statement explains the very high melting temperature of silicon?

   [1 mark]

   • AStrong London forces act between Si₈ molecules
   • BMany strong covalent bonds must be broken in its giant lattice
   • CStrong ionic bonds act between silicon ions
   • DThere is strong attraction between silicon ions and delocalised electrons

   (b)

   Which statement explains why magnesium has a higher melting temperature than sodium?

   [1 mark]

   • AMg²⁺ ions have a greater charge and each atom donates two electrons to the delocalised sea, so metallic bonding is stronger
   • BMagnesium has stronger London forces between its atoms
   • CMagnesium atoms form covalent molecules
   • DMagnesium ions are larger, so they hold the delocalised electrons more strongly

   (c)

   Explain why aluminium has a much higher melting temperature than phosphorus.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Phosphorus exists as P₄ molecules, sulfur as S₈ molecules and chlorine as Cl₂ molecules. Their melting temperatures are 44 °C, 115 °C and −101 °C respectively.

   (a)

   Which forces are overcome when solid sulfur melts?

   [1 mark]

   • ACovalent bonds between the sulfur atoms in each molecule
   • BMetallic bonds between sulfur atoms
   • CIonic bonds between sulfur ions
   • DLondon forces between S₈ molecules

   (b)

   Which statement explains why chlorine has a lower melting temperature than sulfur?

   [1 mark]

   • AThe Cl–Cl covalent bond is weaker than the S–S covalent bond
   • BChlorine has a giant covalent structure
   • CCl₂ molecules have fewer electrons than S₈ molecules, so the London forces are weaker
   • DChlorine consists of ions that are easily separated

   (c)

   Explain why sulfur has a higher melting temperature than phosphorus.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The first ionisation energies of the Period 2 elements, in kJ mol⁻¹, are: Li 520, Be 900, B 801, C 1086, N 1402, O 1314, F 1681 and Ne 2081.

   (a)

   Explain the general increase in first ionisation energy from lithium to neon.

   [3 marks]

   (b)

   Explain why the first ionisation energy of oxygen is lower than that of nitrogen.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Data for the Period 3 elements, given as melting temperature (°C) / atomic radius (nm) / first ionisation energy (kJ mol⁻¹): Na 98 / 0.186 / 496; Mg 650 / 0.160 / 738; Al 660 / 0.143 / 578; Si 1410 / 0.118 / 786; P 44 / 0.110 / 1012; S 115 / 0.103 / 1000; Cl −101 / 0.099 / 1251; Ar −189 / no value / 1521.

   (a)

   Explain the trend in melting temperature from sodium to argon in terms of structure and bonding.

   [6 marks]

   (b)

   Explain the trend in atomic radius from sodium to chlorine and the general trend in first ionisation energy from sodium to argon, including why the values for aluminium and sulfur are lower than expected.

   [6 marks]

   Total for question 4: 12 marks

End of questions