Draw the Lewis structure of CO in its best resonance form. Include all unshared electrons in your drawing.
The correct answer and explanation is :
The best resonance form of carbon monoxide (CO) has a triple bond between the carbon and oxygen atoms, with a lone pair on each atom. The Lewis structure is as follows:
:C≡O:Step-by-Step Explanation:
- Count the Valence Electrons:
- Carbon (C) has 4 valence electrons.
- Oxygen (O) has 6 valence electrons.
- Total valence electrons = 4 + 6 = 10 electrons.
- Determine the Bonding:
Since carbon and oxygen are bonded together, we arrange them with at least a single bond and distribute the remaining electrons. However, a single bond would not satisfy the octet rule for both atoms. - Create a Triple Bond:
- To satisfy the octet rule, carbon and oxygen form a triple bond (one sigma and two pi bonds).
- Carbon donates one of its lone pairs to form a coordinate covalent bond, resulting in a formal charge on both atoms.
- Assign Formal Charges:
Formal charge is calculated using:
[
\text{Formal Charge} = \text{Valence Electrons} – \text{Nonbonding Electrons} – \frac{\text{Bonding Electrons}}{2}
]
- Carbon: (4 – 2 – \frac{6}{2} = -1) → Negative charge
- Oxygen: (6 – 4 – \frac{6}{2} = +1) → Positive charge
- Final Structure:
The best resonance form has a triple bond with a negative charge on carbon and a positive charge on oxygen:
:C≡O:
- +- Why This is the Best Form:
- It satisfies the octet rule for both atoms.
- The formal charges are minimal, and carbon (less electronegative) holds the negative charge.
- Other structures (double bond or single bond forms) would lead to incomplete octets or higher formal charges.
Thus, this Lewis structure represents CO’s most stable resonance form.