The structures of Nocl,No2,Cl,No3,Cl
and
were determined in
They have the skeletal structures shown in Figure
Draw Lewis structures for the three compounds and predict the electron-pair geometry at each nitrogen atom.
The Correct Answer and Explanation is:
To analyze the compounds NOCl, Cl₂, and NO₃⁻, we will draw their Lewis structures and predict the electron-pair geometry around each nitrogen atom using VSEPR theory. Only NOCl and NO₃⁻ contain nitrogen, so Cl₂ will not be included in the nitrogen geometry discussion.
Lewis Structures and Geometries
1. NOCl (Nitrosyl chloride)
- Total valence electrons: N (5) + O (6) + Cl (7) = 18 electrons
- Structure: N is the central atom bonded to O and Cl.
- Make a double bond with O, a single bond with Cl, and put a lone pair on N.
- Electron domains around N: 1 lone pair, 2 bonded atoms = 3 regions
- Electron-pair geometry at N: Trigonal planar
- Molecular geometry: Bent
2. Cl₂ (Chlorine molecule)
- Total valence electrons: 2 × Cl (7) = 14 electrons
- Structure: A single bond between two Cl atoms, each with 3 lone pairs.
- No nitrogen is present → no electron-pair geometry at N to discuss.
3. NO₃⁻ (Nitrate ion)
- Total valence electrons: N (5) + 3×O (6) + 1 extra e⁻ = 24 electrons
- Structure: N is central, with three N–O bonds and one negative charge delocalized.
- Resonance structures: All three N–O bonds are equivalent due to delocalization.
- No lone pair on N; 3 bonding domains = 3 regions
- Electron-pair geometry at N: Trigonal planar
- Molecular geometry: Trigonal planar
Explanation
The Lewis structures and geometries of NOCl, Cl₂, and NO₃⁻ provide insight into the behavior of nitrogen in different chemical environments. In NOCl (nitrosyl chloride), the nitrogen atom forms a double bond with oxygen and a single bond with chlorine. It also retains one lone pair, creating three regions of electron density around the nitrogen atom. According to VSEPR theory, these regions arrange themselves to minimize repulsion, resulting in a trigonal planar electron-pair geometry. However, because one of these regions is a lone pair, the actual molecular geometry is bent, with bond angles slightly less than 120°.
In contrast, Cl₂ is a diatomic molecule composed solely of chlorine atoms connected by a single bond. It contains no nitrogen, so it doesn’t contribute to the discussion of nitrogen’s geometry. Each chlorine has three lone pairs and shares one bonding pair, resulting in a linear structure overall.
The nitrate ion (NO₃⁻) presents a different scenario for nitrogen. Here, the nitrogen atom is bonded to three oxygen atoms through resonance-stabilized structures. Each N–O bond is equivalent due to electron delocalization, and nitrogen holds no lone pairs, only three bonding domains. This leads to a trigonal planar electron-pair geometry, and since all electron regions are bonding, the molecular geometry is also trigonal planar, with ideal bond angles of 120°.
In summary, nitrogen in NOCl adopts a bent geometry due to a lone pair, while in NO₃⁻, it adopts a flat, symmetric trigonal planar structure due to resonance and lack of lone pairs. These variations demonstrate how electron configuration directly influences molecular shape and behavior.
