Question 22M.2.sl.TZ2.a
| Date | May 2022 | Marks available | [Maximum mark: 2] | Reference code | 22M.2.sl.TZ2.a |
| Level | sl | Paper | 2 | Time zone | TZ2 |
| Command term | Explain | Question number | a | Adapted from | N/A |
Electrons are arranged in energy levels around the nucleus of an atom.
Explain why the first ionization energy of calcium is greater than that of potassium.
[2]
increasing number of protons/nuclear charge/Zeff ✔
«atomic» radius/size decreases
OR
same number of energy levels
OR
similar shielding «by inner electrons» ✔
It was surprising that this question that appears regularly in IB chemistry papers was not better answered. Many candidates only obtained one of the two marks for identifying one factor (often the larger nuclear charge of calcium or that the number of shells was the same for Ca and K). However, a few candidates did write thorough answers reflecting a good understanding of the factors affecting ionization energy. This question had a strong correlation between candidates who scored well and those who had a high score overall. Some candidates did not score any marks by focusing on trends in the Periodic Table without offering an explanation, or by discussing the number of electrons in Ca and K instead of the number of protons.
