The Lewis structure of HCN (H bonded to C) shows that has non bonding electron pairs.
A) C. 1
B) N, 2
C) C, 2
D) N,1
The correct answer and explanation is :
The correct answer is D) N, 1.
Explanation:
In order to understand the number of non-bonding electron pairs in the Lewis structure of hydrogen cyanide (HCN), we need to follow these steps:
- Determine the Valence Electrons:
- Hydrogen (H) has 1 valence electron.
- Carbon (C) has 4 valence electrons.
- Nitrogen (N) has 5 valence electrons. The total number of valence electrons in HCN is:
[
1 (\text{H}) + 4 (\text{C}) + 5 (\text{N}) = 10 \text{ electrons}.
]
- Construct the Lewis Structure:
- HCN consists of three atoms: hydrogen (H), carbon (C), and nitrogen (N).
- Hydrogen is always bonded to only one other atom because it needs only two electrons to complete its valence shell.
- Carbon can form four bonds, and nitrogen can form three bonds to complete its valence shell. The most likely bonding arrangement for HCN is:
- H is bonded to C.
- C is bonded to N with a triple bond (C≡N). The electrons from the triple bond between C and N fill the valence requirements for both atoms. After forming the bonds, the remaining electrons are placed as lone pairs.
- Assign Non-Bonding Electrons:
- Hydrogen (H) has no lone pairs because it is involved in a single bond with carbon.
- Carbon (C) also has no lone pairs since all of its electrons are involved in bonding (one single bond with hydrogen and one triple bond with nitrogen).
- Nitrogen (N), on the other hand, has one lone pair because, after forming a triple bond with carbon, it has one remaining electron pair. This lone pair constitutes a non-bonding pair of electrons.
Therefore, nitrogen (N) has 1 lone pair (non-bonding electrons), and the correct answer is D) N, 1.
This is the Lewis structure of HCN:
H - C ≡ NWhere the nitrogen atom has one lone pair of electrons.