DP Chemistry (last assessment 2024)
Question 19M.3.hl.TZ1.d(ii)
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.3.hl.TZ1.d(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.d(ii)
Lithium has many uses.
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.
