Which allotropes of carbon are electrical conductors?
I. Graphite
II. Diamond
III. Graphene
Correct Answer: \( \boxed{\mathrm{B}} \)
Graphite: Each carbon atom forms three covalent bonds, leaving one electron delocalised. These delocalised electrons can move through the layers, allowing graphite to conduct electricity.
Diamond: Each carbon atom forms four covalent bonds. All four outer electrons are involved in bonding, so there are no delocalised electrons available to carry charge. Diamond therefore does not conduct electricity.
Graphene: Each carbon atom forms three covalent bonds, with one electron delocalised across the structure. Graphene therefore conducts electricity.
Thus, graphite and graphene are electrical conductors, so the correct answer is (B).
Which compound has the highest boiling point?
Correct Answer: \( \boxed{\mathrm{B}} \)
All four compounds are alkanes, so their main intermolecular force is London dispersion forces.
For alkanes with similar structures, increasing molecular size and surface area generally increases the strength of London dispersion forces and therefore increases the boiling point.
Compound B, \( \mathrm{CH_3CH_2CH_2CH_2CH_2CH_3} \), is a straight-chain alkane with six carbon atoms. It has a larger surface area and stronger dispersion forces than the smaller or more highly branched alternatives.
Therefore, compound B has the highest boiling point, so the correct answer is (B).
Which material is a good electrical conductor?
Correct Answer: \( \boxed{\mathrm{B}} \)
Graphite is a good electrical conductor because each carbon atom forms three covalent bonds and has one electron that is delocalised across the layers.
These delocalised electrons are able to move through the structure and carry electrical charge.
Diamond does not conduct electricity because all four valence electrons of each carbon atom are involved in covalent bonds. Fullerene has much less extensive electron delocalisation, while silicon is a semiconductor.
Therefore, the correct answer is (B).
