What are the formal charges on O and H in the hydroxide ion (OH⁻)?

In the hydroxide ion (OH⁻), we can determine the formal charges on the oxygen (O) and hydrogen (H) atoms by using the formal charge formula. The formal charge (FC) can be calculated using the formula:

FC = V – (N + B/2)

where:

• V = number of valence electrons in the neutral atom
• N = number of non-bonding electrons (lone pair electrons)
• B = number of bonding electrons (shared electrons in bonds)

For oxygen (O):

• Valence electrons (V) = 6
• Non-bonding electrons (N) = 4 (the two lone pairs)
• Bonding electrons (B) = 2 (the single bond with hydrogen)

Plugging these values into the formula:

FC_O = 6 – (4 + 2/2) = 6 – (4 + 1) = 6 – 5 = 1

So the formal charge on the oxygen atom is +1.

For hydrogen (H):

• Valence electrons (V) = 1
• Non-bonding electrons (N) = 0
• Bonding electrons (B) = 2 (the single bond with oxygen)

Now using the formula:

FC_H = 1 – (0 + 2/2) = 1 – (0 + 1) = 1 – 1 = 0

Thus, the formal charge on the hydrogen atom is 0.

In summary, in the hydroxide ion (OH⁻), the formal charge on oxygen is +1 and on hydrogen is 0. Therefore, the correct answer is:

a) 1, 0