DP Chemistry (first assessment 2025)
Question 19M.1A.HL.TZ2.12
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.1A.HL.TZ2.12 |
| Level | HL | Paper | 1A | Time zone | TZ2 |
| Command term | Question number | 12 | Adapted from | N/A |
12.
[Maximum mark: 1]
19M.1A.HL.TZ2.12
How many sigma (σ) and pi (π) bonds are present in hydrogen cyanide, HCN?
[1]
Markscheme
B
Examiners report
89 % of the candidates deduced the numbers of sigma and pi bonds in HCN correctly. The most commonly chosen distractor (C) had the correct number of sigma bonds but only one pi bond.
Syllabus sections
Structure 2. Models of bonding and structure » Structure 2.2—The covalent model » Structure 2.2.15—Sigma bonds σ form by the head-on combination of atomic orbitals where the electron density is concentrated along the bond axis. Pi bonds π form by the lateral combination of p-orbitals where the electron density is concentrated on opposite sides of the bond axis. Deduce the presence of sigma bonds and pi bonds in molecules and ions.