Draw the Lewis dot structure of Nitrous Acid (HNO2) the structure has a total of valence electrons. The central atom is ? (what atom) For the central atom the molecule contains a total of: bonds (answer with numbers) single bonds double bonds free pairs of electrons What is the electronic geometry for the central atom ?
The Correct Answer and Explanation is:
Sure! Let’s break down the problem step-by-step for Nitrous Acid (HNO₂):
Step 1: Determine the total number of valence electrons
- H (Hydrogen): 1 valence electron
- N (Nitrogen): 5 valence electrons
- O (Oxygen): 6 valence electrons × 2 = 12 valence electrons
Total valence electrons = 1 + 5 + 12 = 18 valence electrons
Step 2: Identify the central atom
- Hydrogen can never be the central atom (it only forms 1 bond).
- Between Nitrogen and Oxygen, Nitrogen is less electronegative and usually acts as the central atom.
Central atom = Nitrogen (N)
Step 3: Draw a basic skeleton and assign bonds
- Nitrogen connects to Hydrogen (H).
- Nitrogen connects to two Oxygen atoms.
- So, the skeleton is: H — N — O and N — O
Step 4: Distribute electrons and make bonds
Lewis structure of HNO₂:
O
||
H — N — O
..
- Nitrogen forms one single bond with Hydrogen.
- Nitrogen forms one double bond with one Oxygen atom.
- Nitrogen forms one single bond with the other Oxygen atom.
- The single-bonded Oxygen has 2 lone pairs (4 electrons).
- The double-bonded Oxygen has 2 lone pairs (4 electrons).
- Nitrogen has 1 lone pair.
Step 5: Count bonds and lone pairs
- Single bonds: 2 (N-H and N-O single bond)
- Double bonds: 1 (N=O double bond)
- Lone pairs:
- On nitrogen: 1 lone pair
- On oxygen atoms:
- Single-bonded oxygen: 2 lone pairs
- Double-bonded oxygen: 2 lone pairs
Step 6: Electronic geometry of central atom (Nitrogen)
- Nitrogen has 3 bonding pairs (2 single + 1 double bond) and 1 lone pair.
- Total electron regions around nitrogen = 4.
According to VSEPR theory:
- 4 regions of electron density → Tetrahedral electronic geometry
- Because one is a lone pair, the molecular shape is Trigonal pyramidal.
Final answers:
| Question | Answer |
|---|---|
| Total valence electrons | 18 |
| Central atom | Nitrogen (N) |
| Number of single bonds | 2 |
| Number of double bonds | 1 |
| Number of lone pairs (free pairs) | 5 (1 on N, 4 on O) |
| Electronic geometry of central atom | Tetrahedral |
Explanation
Nitrous acid (HNO₂) consists of one hydrogen atom, one nitrogen atom, and two oxygen atoms. To construct its Lewis structure, we begin by counting the total valence electrons. Hydrogen contributes 1 electron, nitrogen 5 electrons, and oxygen 6 electrons each, adding up to 18 valence electrons.
The central atom is usually the least electronegative atom that can form multiple bonds, which is nitrogen in this case. Hydrogen can only form one bond, and oxygen is more electronegative, so nitrogen serves as the central atom connecting to hydrogen and the two oxygen atoms.
The Lewis structure of HNO₂ features nitrogen bonded to hydrogen through a single bond, bonded to one oxygen via a double bond, and bonded to the other oxygen with a single bond. Each oxygen atom completes its octet by holding lone pairs: two lone pairs for the single-bonded oxygen and two lone pairs for the double-bonded oxygen. Nitrogen itself also holds one lone pair to satisfy the octet rule.
Counting the bonds reveals there are two single bonds (N–H and N–O single) and one double bond (N=O). Lone pairs total to five: one on nitrogen and four spread on the oxygens.
In terms of molecular geometry, nitrogen has four regions of electron density (three bonds and one lone pair), which corresponds to a tetrahedral electronic geometry according to VSEPR theory. However, because one of those regions is a lone pair, the actual molecular shape (the arrangement of atoms) is trigonal pyramidal.
This structure explains the bonding and geometry, helping predict chemical reactivity and physical properties like polarity of nitrous acid.
