Question

based on formal charge arguments, which molecule is the more appropriate structure for nh₃o? images of two lewis structures and an option both structures are equally appropriate

Explanation:

To determine the more appropriate structure for \( \text{NH}_3\text{O} \) (likely \( \text{H}_3\text{NO} \) or related) using formal charge, we calculate formal charge for each atom in both structures. The formula for formal charge is:
\( \text{Formal Charge} = \text{Valence Electrons} - \text{Non - bonding Electrons} - \frac{1}{2}\text{Bonding Electrons} \)

Structure 1 (Top: \( \text{H}_3\text{N}-\text{O} \) with lone pairs on O)

• Nitrogen (N): Valence electrons = 5. Non - bonding electrons = 0. Bonding electrons = 8 (4 single bonds: \( \text{N}-\text{H} \) (3) and \( \text{N}-\text{O} \) (1)).

\( \text{FC}(N)=5 - 0-\frac{8}{2}=5 - 4 = + 1 \)

• Oxygen (O): Valence electrons = 6. Non - bonding electrons = 6 (3 lone pairs). Bonding electrons = 2 (1 single bond to N).

\( \text{FC}(O)=6 - 6-\frac{2}{2}=6 - 6 - 1=-1 \)

• Hydrogen (H): Valence electrons = 1. Non - bonding electrons = 0. Bonding electrons = 2 (1 single bond each).

\( \text{FC}(H)=1 - 0-\frac{2}{2}=0 \)

Structure 2 (Middle: \( \text{H}_2\text{N}-\text{O}-\text{H} \) with lone pair on N)

• Nitrogen (N): Valence electrons = 5. Non - bonding electrons = 2 (1 lone pair). Bonding electrons = 6 (3 single bonds: \( \text{N}-\text{H} \) (2) and \( \text{N}-\text{O} \) (1)).

\( \text{FC}(N)=5 - 2-\frac{6}{2}=5 - 2 - 3 = 0 \)

• Oxygen (O): Valence electrons = 6. Non - bonding electrons = 4 (2 lone pairs). Bonding electrons = 4 (2 single bonds: \( \text{O}-\text{N} \) and \( \text{O}-\text{H} \)).

\( \text{FC}(O)=6 - 4-\frac{4}{2}=6 - 4 - 2 = 0 \)

• Hydrogen (H): Valence electrons = 1. Non - bonding electrons = 0. Bonding electrons = 2 (1 single bond each).

\( \text{FC}(H)=1 - 0-\frac{2}{2}=0 \)

Analysis of Formal Charges

In Structure 1, N has \( + 1 \) and O has \( - 1 \) (non - zero formal charges). In Structure 2, all atoms (N, O, H) have a formal charge of 0. A structure with more atoms having zero formal charge is generally more stable and appropriate.

Answer:

The middle structure (with \( \text{H}_2\text{N}-\text{O}-\text{H} \) and a lone pair on N) is the more appropriate structure.