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Date May 2021 Marks available 2 Reference code 21M.2.sl.TZ2.2
Level SL Paper 2 Time zone TZ2
Command term State Question number 2 Adapted from N/A

Question

The properties of elements can be predicted from their position in the periodic table.

Explain why Si has a smaller atomic radius than Al.

[2]
a(i).

Explain the decrease in radius from Na to Na+.

[2]
a(ii).

State the condensed electron configurations for Cr and Cr3+.

[2]
b(i).

Describe metallic bonding and how it contributes to electrical conductivity.

[3]
b(ii).

Deduce the Lewis (electron dot) structure and molecular geometry of sulfur dichloride, SCl2.

[2]
c.

Suggest, giving reasons, the relative volatilities of SCl2 and H2O.

[3]
d.

Consider the following equilibrium reaction:

2SO2 (g) + O2 (g) 2SO3 (g)

State and explain how the equilibrium would be affected by increasing the volume of the reaction container at a constant temperature.

[3]
e.

Markscheme

nuclear charge/number of protons/Z/Zeff increases «causing a stronger pull on the outer electrons» ✓

same number of shells/«outer» energy level/shielding ✓

a(i).

Na+ has one less energy level/shell
OR
Na+ has 2 energy levels/shells AND Na has 3 ✓

less shielding «in Na+ so valence electrons attracted more strongly to nucleus»
OR
effective nuclear charge/Zeff greater «in Na+ so valence electrons attracted more strongly to nucleus» ✓


Accept “more protons than electrons «in Na+»” OR “less electron-electron repulsion «in Na+»” for M2.

a(ii).

Cr:
[Ar] 4s13d5


Cr3+:

[Ar] 3d3


Accept “[Ar] 3d54s1”.

Accept “[Ar] 3d34s0”.

Award [1 max] for two correct full electron configurations “1s22s22p63s23p64s13d5 AND 1s22s22p63s23p63d3”.

Award [1 max] for 4s13d5 AND 3d3.

b(i).

electrostatic attraction ✓

between «a lattice of» cations/positive «metal» ions AND «a sea of» delocalized electrons ✓


mobile electrons responsible for conductivity
OR
electrons move when a voltage/potential difference/electric field is applied ✓

 

Do not accept “nuclei” for “cations/positive ions” in M2.

Accept “mobile/free” for “delocalized” electrons in M2.

Accept “electrons move when connected to a cell/battery/power supply” OR “electrons move when connected in a circuit” for M3.

b(ii).

c.

H2O forms hydrogen bonding «while SCl2 does not» ✓

SCl2 «much» stronger London/dispersion/«instantaneous» induced dipole-induced dipole forces ✓


Alternative 1:

H2O less volatile AND hydrogen bonding stronger «than dipole–dipole and dispersion forces» ✓


Alternative 2:

SCl2 less volatile AND effect of dispersion forces «could be» greater than hydrogen bonding ✓\

 

Ignore reference to Van der Waals.

Accept “SCl2 has «much» larger molar mass/electron density” for M2.

d.

pressure decrease «due to larger volume» ✓

reactant side has more moles/molecules «of gas» ✓

reaction shifts left/towards reactants ✓


Award M3 only if M1 OR M2 is awarded.

e.

Examiners report

[N/A]
a(i).
[N/A]
a(ii).
[N/A]
b(i).
[N/A]
b(ii).
[N/A]
c.
[N/A]
d.
[N/A]
e.

Syllabus sections

Core » Topic 2: Atomic structure » 2.2 Electron configuration
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