Which statement about covalent bonding and molecular geometry is correct?
In a molecule of hydrogen cyanide (HCN\text{HCN}HCN), there are two σ\sigmaσ-bonds and two π\piπ-bonds, and the H-C-N\text{H-C-N}H-C-N bond angle is 180∘180^\circ180∘.
In methanal (HCHO\text{HCHO}HCHO), the H-C-H\text{H-C-H}H-C-H bond angle is 109.5∘109.5^\circ109.5∘ because the four bonding electron pairs around the carbon atom adopt a tetrahedral geometry.
A π\piπ-bond is formed by the end-on overlap of p-orbitals, which results in a higher bond enthalpy than a σ\sigmaσ-bond.
The single σ\sigmaσ-bond in ethane (C2H6\text{C}_2\text{H}_6C2H6) prevents the rotation of the methyl groups around the carbon-carbon bond axis.
31 exam-style questions on OCR A A Level Chemistry Bonding and structure. Each one has a worked solution and a mark scheme showing where the marks go.