DP Chemistry (first assessment 2025)
Question 22N.1A.SL.TZ0.10
| Date | November 2022 | Marks available | [Maximum mark: 1] | Reference code | 22N.1A.SL.TZ0.10 |
| Level | SL | Paper | 1A | Time zone | TZ0 |
| Command term | Predict | Question number | 10 | Adapted from | N/A |
10.
[Maximum mark: 1]
22N.1A.SL.TZ0.10
Which molecule is polar?
A. BeH2
B. AlH3
C. PH3
D. SiH4
[1]
Markscheme
C
Examiners report
A well-answered question - 61% of the candidates selected PH3 as the polar molecule as the dipoles in the other symmetrical molecules would cancel out due to the molecular geometry. The question also discriminated well between high-scoring and low-scoring candidates. Some teachers were unhappy about the question as the electronegativities of P and H in the data booklet (which the students did not have access to in this paper) are identical. Apologies for this choice - a better example should have been used.
Syllabus sections
Structure 2. Models of bonding and structure » Structure 2.2—The covalent model » Structure 2.2.13—Some atoms can form molecules in which they have an expanded octet of electrons. Visually represent Lewis formulas for species with five and six electron domains around the central atom. Deduce the electron domain geometry and the molecular geometry for these species using the VSEPR model.