Question 18M.3.sl.TZ2.2a
| Date | May 2018 | Marks available | [Maximum mark: 2] | Reference code | 18M.3.sl.TZ2.2a |
| Level | sl | Paper | 3 | Time zone | TZ2 |
| Command term | Describe | Question number | a | Adapted from | N/A |
Organic molecules can be visualized using three-dimensional models built from kits such as that pictured below.
Describe two differences, other than the number of atoms, between the models of ethane and ethene constructed from the kit shown.
[2]
Any two of:
Ethene: «carbon–carbon» double bond AND Ethane: «carbon–carbon» single bond
ethene has a shorter carbon–carbon bond «than ethane»
Ethene: planar/two-dimensional/2-D AND Ethane: tetrahedral «carbons»/three-dimensional/3-D
OR
Ethene: each carbon surrounded by three electron domains AND Ethane: each carbon surrounded by four electron domains
OR
different molecular geometries/shapes
rotation about carbon–carbon inhibited/blocked in ethene AND not in ethane
«H–C–C/H–C–H» bond angles different
OR
Ethene: «bond angles approximately» 120° AND Ethane: 109.5/109°
Do not accept “different number of atoms/hydrogens/bonds” etc.
Accept “Ethene: unsaturated AND Ethane: saturated” OR “Ethene: has a double bond AND Ethane: does not” OR “Ethene: two flexible bonds between carbon atoms AND Ethane: one”.
Accept any reasonable physical description of the two different molecular models based on a variety of kits for M1.
For ethene, accept any bond angle in the range 117–122°.
Award [2] if any two of the concepts listed are shown in a correctly labelled or annotated diagram.
Award [1 max] for two correct statements for either molecule but with no comparison given to the other.
Award [1 max] for suitable unlabeled diagrams of both compounds.
[2 marks]