What is the molecular shape of HCN?
The Correct Answer and Explanation is :
The molecular shape of hydrogen cyanide (HCN) is linear. This conclusion is based on the arrangement of atoms and the electron pair geometry around the central carbon atom.
Explanation:
- Molecular Structure: HCN consists of three atoms: hydrogen (H), carbon (C), and nitrogen (N). In this molecule, hydrogen is bonded to carbon, which is then triple-bonded to nitrogen. The structural formula can be represented as H-C≡N.
- Valence Electrons: The valence electron count for HCN is crucial for understanding its shape. Hydrogen contributes one electron, carbon contributes four, and nitrogen contributes five, for a total of 10 valence electrons.
- Bonding: The carbon atom is the central atom in HCN. It forms one single bond with hydrogen and one triple bond with nitrogen. The triple bond consists of one sigma (σ) bond and two pi (π) bonds, which are formed by the overlap of atomic orbitals.
- Electron Geometry: According to VSEPR (Valence Shell Electron Pair Repulsion) theory, the arrangement of electron pairs around the carbon atom determines the molecular shape. In HCN, there are two regions of electron density around the carbon atom (one single bond with hydrogen and one triple bond with nitrogen). Since there are no lone pairs of electrons on the carbon atom, the electron pair geometry is linear.
- Molecular Shape: With a linear arrangement of electron pairs, the H-C≡N molecule adopts a straight-line shape. The bond angles between the atoms are approximately 180 degrees, confirming the linear structure.
- Dipole Moment: Due to the difference in electronegativity between carbon and nitrogen, HCN is a polar molecule. However, the linear shape allows the dipole moments to be aligned along the same axis, resulting in a net dipole moment.
In summary, the linear shape of HCN is a result of the bonding and arrangement of atoms, consistent with the principles of VSEPR theory.