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Date May 2018 Marks available 2 Reference code 18M.2.hl.TZ2.7
Level HL Paper 2 Time zone TZ2
Command term Identify Question number 7 Adapted from N/A

Question

Some physical properties of molecular substances result from the different types of forces between their molecules.

Resonance structures exist when a molecule can be represented by more than one Lewis structure.

Carbon dioxide can be represented by at least two resonance structures, I and II.

M18/4/CHEMI/HP2/ENG/TZ2/07.c.i_01

Calculate the formal charge on each oxygen atom in the two structures.

M18/4/CHEMI/HP2/ENG/TZ2/07.c.i_02

[2]
c.i.

Deduce, giving a reason, the more likely structure.

[1]
c.ii.

Absorption of UV light in the ozone layer causes the dissociation of oxygen and ozone.

Identify, in terms of bonding, the molecule that requires a longer wavelength to dissociate.

[2]
d.

Carbon and silicon are elements in group 14.

Explain why CO2 is a gas but SiO2 is a solid at room temperature.

[2]
e.

Markscheme

M18/4/CHEMI/HP2/ENG/TZ2/07.c.i/M

 

Award [1] for any two correctly filled cells.

[2 marks]

c.i.

structure I AND no formal charges

OR

structure I AND no charge transfer «between atoms»

[1 mark]

c.ii.

O3 has bond between single and double bond AND O2 has double bond

OR

O3 has bond order of 1.5 AND O2 has bond order of 2

OR

bond in O3 is weaker/longer than in O2

 

O3 requires longer wavelength

 

M1: Do not accept “ozone has one single and one double bond”.

[2 marks]

d.

CO2 «non-polar» «weak» London/dispersion forces/instantaneous induced dipole-induced dipole forces between molecules

SiO2 network/lattice/3D/giant «covalent» structure

 

M1: The concept of “between” is essential.

[2 marks]

e.

Examiners report

[N/A]
c.i.
[N/A]
c.ii.
[N/A]
d.
[N/A]
e.

Syllabus sections

Additional higher level (AHL) » Topic 14: Chemical bonding and structure » 14.1 Covalent bonding and electron domain and molecular geometries
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Additional higher level (AHL) » Topic 14: Chemical bonding and structure
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