DP Chemistry (last assessment 2024)
Question 19M.3.hl.TZ1.3d(ii)
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.3.hl.TZ1.3d(ii) |
| Level | hl | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | d(ii) | Adapted from | N/A |
d(ii).
[Maximum mark: 3]
19M.3.hl.TZ1.3d(ii)
Lithium has many uses.
(d(ii))
At very low temperatures, lithium atoms enhance the phonon binding of electrons in graphene suggesting the formation of Cooper pairs.
Explain how Cooper pairs are formed.
[3]
Markscheme
Any three of:
positive ions/cations in lattice are attracted to passing electron [✔]
lattice is distorted «by this passing electron» [✔]
creates «local» regions of increased positive charge [✔]
second electron is attracted to deformation AND a coupling occurs [✔]
Examiners report
Poor expression was also evident in responses explaining the formation of Cooper pairs, with very few candidates scoring full marks.
