Draw the Lewis structure of nitrous acid (HNO₂) and then choose the appropriate pair of molecular geometries of the two central atoms. Your answer choice is independent of the orientation of your drawn structure.
A) bent (109.5°) / bent (120°)
B) bent (109.5°) / tetrahedral
C) bent (109.5°) / planar
D) trigonal planar / bent (109.5°)
E) bent (120°)/ planar
The Correct Answer and Explanation is :
The Lewis structure of nitrous acid (HNO₂) consists of a nitrogen (N) atom bonded to one hydrogen (H) and two oxygen (O) atoms. One oxygen is doubly bonded to nitrogen, while the other oxygen is singly bonded and also carries a negative charge.
Molecular Geometry Explanation:
In HNO₂, there are two central atoms: nitrogen (N) and the oxygen atom involved in the single bond. We need to determine the molecular geometries based on the electron domain theory and VSEPR (Valence Shell Electron Pair Repulsion) model.
- Nitrogen (N) Atom:
- The nitrogen atom has three regions of electron density: one single bond to hydrogen, one single bond to an oxygen, and one double bond to the other oxygen.
- These three regions of electron density arrange themselves in a trigonal planar geometry, with bond angles approximately 120° due to repulsion between bonding pairs of electrons.
- Oxygen (O) Atom (Single Bond to Nitrogen):
- The oxygen atom that is single-bonded to nitrogen has a lone pair of electrons and a single bond to nitrogen, creating two regions of electron density.
- This results in a bent molecular geometry, with an angle of about 120° between the bonds due to the lone pair repulsion.
Answer Choice:
- D) trigonal planar / bent (109.5°) is the correct answer. The nitrogen atom has a trigonal planar geometry with approximately 120° bond angles, and the oxygen atom attached to nitrogen with a single bond adopts a bent geometry with bond angles closer to 109.5°, which is typical for molecules with lone pairs on oxygen.
