Question

What is the formal charge of oxygen atom in carbon monoxide?

• A. +2
• B. +1
• C. -1
• D. zero

Hint:

Oxygen normally forms 2 covalent bonds and holds 2 lone pairs, resulting in a neutral state (formal charge = 0).
When oxygen forms a third bond by donating one of its lone pairs to an electron-deficient atom (like carbon in CO), it effectively "loses" a share of an electron, which gives it a formal charge of $+1$.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The problem requires us to determine the formal charge assigned to the oxygen atom within a stable carbon monoxide (CO) molecule.

Step 2: Key Formula or Approach:
The standard formula to compute the formal charge of an atom within a Lewis structure is:
$$\text{Formal Charge} = V - L - \frac{1}{2}S$$
Where:
$V = $ Number of valence electrons in the free, isolated atom.
$L = $ Number of electrons belonging to lone pairs on that atom.
$S = $ Number of shared bonding electrons surrounding that atom.

Step 3: Detailed Explanation:
Let's analyze the Lewis structure of carbon monoxide (CO).
Carbon has 4 valence electrons and Oxygen has 6 valence electrons, giving a total of 10 valence electrons to distribute.
To satisfy the octet rule for both elements, carbon and oxygen share three electron pairs, forming a triple bond ($:\text{C} \equiv \text{O}:$). Each atom also retains one lone pair.
Let's double-check the octets:
Carbon has 2 non-bonding electrons + 6 shared electrons = 8 electrons.
Oxygen has 2 non-bonding electrons + 6 shared electrons = 8 electrons.
Now, let's calculate the formal charge specifically for the Oxygen atom:
Valence electrons of isolated oxygen ($V$) = 6
Lone pair non-bonding electrons ($L$) = 2
Shared bonding electrons ($S$) = 6 (from the triple bond)
Apply these values to the formal charge equation:
$$\text{Formal Charge} = 6 - 2 - \frac{1}{2}(6) = 4 - 3 = +1$$
(For comparison, the carbon atom carries a balancing formal charge of $4 - 2 - \frac{1}{2}(6) = -1$).

Step 4: Final Answer:
The formal charge of the oxygen atom in the Lewis structure of carbon monoxide is +1, which corresponds to option (B).