Draw the Lewis structure of: a) COBr2. The Carbon isin the center and bonded to the Oxygen and to the two Bromine atoms. b) Ammonium Ion.
The Correct Answer and Explanation is:
a) Lewis Structure of COBr₂ (Carbonyl dibromide)
Structure:
..
Br – C = O
|
Br
..
Explanation:
Carbon is the central atom and forms:
- One double bond with oxygen (C=O)
- Two single bonds with bromine atoms (C–Br)
Steps:
- Count total valence electrons:
- Carbon (C): 4
- Oxygen (O): 6
- Bromine (Br): 7 × 2 = 14
→ Total = 4 + 6 + 14 = 24 electrons
- Connect atoms with single bonds:
- C–O and two C–Br bonds use 6 electrons (3 bonds × 2 e⁻)
- Complete the octets for O and Br:
- Oxygen needs 6 more electrons (3 lone pairs)
- Each Br needs 6 more electrons (3 lone pairs)
- That’s 6 + 6 + 6 = 18 electrons
→ Total used = 6 (bonds) + 18 (lone pairs) = 24 electrons — matches total.
- Check octets:
- Carbon has only 6 electrons so far. To complete its octet, form a double bond with oxygen.
→ Final structure:
- C=O double bond
- Two single bonds to Br
- Oxygen has 2 lone pairs
- Each Br has 3 lone pairs
b) Lewis Structure of Ammonium Ion (NH₄⁺)
Structure:
H
|
H – N – H
|
H
The entire ion is enclosed in brackets with a “⁺” charge: | H H \]⁺ **Explanation:** 1. **Count valence electrons:** – Nitrogen: 5 – Hydrogen: 1 × 4 = 4 – Positive charge = **–1 electron** → Total = 5 + 4 – 1 = **8 electrons** 2. **Form four N–H single bonds:** – 4 bonds × 2 electrons = 8 electrons — all used. 3. **No lone pairs** on nitrogen, as all electrons are in bonding. 4. **Formal charge:** – Nitrogen: normally 5 valence electrons; now surrounded by 4 bonds (0 lone pairs) → 5 – 4 = **+1 charge** This explains the **positive charge** on the ammonium ion. — ### Summary: – **COBr₂** has 24 valence electrons; carbon forms a double bond with oxygen and single bonds with two bromines. Oxygen and bromines have lone pairs; carbon satisfies the octet via a double bond. – **Ammonium ion (NH₄⁺)** forms four N–H bonds, uses 8 electrons, and has a formal positive charge due to the proton donation (H⁺), leaving nitrogen without lone pairs and with a +1 charge.
