Blueprint MCAT Formerly Next Step
Return to Blog Homepage

PCAT Chemical Processes – Oxygen

What are the formal charges on oxygen A, carbon, and oxygen B in this resonance structure of CO2?

mcat sample question biology

A) -1, 0, -3

B) +2, 0, +2

C) +1, 0, -1

D) +5, +4, +7

Click for Explanation

Formal charge = valence e – ( e in lone pairs + 1/2 bonded e)

Stated more loosely, the formal charge is the number of electrons an atom “wants” to have minus the dots minus the sticks. So, for example, for the oxygen on the left, we know that oxygen “wants” to have six electrons. It’s got two dots and three sticks. So 6 – 2 – 3 = +1

A) -1, 0, -3, incorrect, Uses formal charge = -valence e + ( e in lone pairs + 1/2 bonded e).

B) 2, 0, 2, incorrect, Uses formal charge = -valence e + ( e in lone pairs + bonded e).

C) 1, 0, -1, correct.

D) 5, 4, 7, incorrect, Uses formal charge = e in lone pairs + 1/2 bonded e.

Submit a Comment

Submit a Comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.