Chemistry · Chemical Bonding · NEET
Formal Charge = V − L − S/2. Here V = number of valence electrons the atom has when it is free (alone). L = number of lone pair (non-bonding) electrons on that atom in the structure. S = number of bonding (shared) electrons around that atom. You take half of S because each bond is shared with another atom. Simple rule: count each bond line as 2 electrons, so a double bond = 4 shared electrons.
Look at ONE atom. L = the dots (non-bonding electrons) sitting only on that atom. Each dot is 1 electron, so a lone pair = 2. S = all electrons in the bond lines touching that atom. One single bond = 2 shared, one double bond = 4 shared, one triple bond = 6 shared. Then plug into V − L − S/2. Do this atom by atom.
The central O forms one double bond and one single bond, so it uses 3 bonds. It has only 1 lone pair left (L = 2). Bonding electrons S = 4 (double) + 2 (single) = 6, so S/2 = 3. Formal charge = 6 − 2 − 3 = +1. Because the central O is 'sharing more' than usual, it looks electron-poor, giving +1. This is a very common NEET question.
No. They are different. Formal charge assumes bonds are shared EQUALLY (pure covalent view), so each atom gets half of every shared pair. Oxidation number assumes the more electronegative atom takes BOTH shared electrons. So for O3, formal charges are 0, +1, −1, but oxidation numbers are all 0. Do not mix them up in the exam.
No. NCERT says clearly that formal charge does NOT show real charge separation in the molecule. It is only a bookkeeping tool to track valence electrons. Its main job is to help you pick the best (lowest energy) Lewis structure among several options.
Draw all possible Lewis structures. The best (most stable, lowest energy) one usually has the SMALLEST formal charges on the atoms, and if there are negative charges, they should sit on the more electronegative atom. So a structure with formal charges near 0 beats one with big +2 or −2 charges.
For the ozone (O3) Lewis structure — a central O atom (1) doubly bonded to one terminal O atom (2) and singly bonded to the other terminal O atom (3) — the correct formal charges on the oxygen atoms numbered 2, 1 and 3 respectively are:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Formal Charge = (number of valence electrons) − (number of lone pair electrons) − ½(number of bonding electrons). In short: FC = V − L − S/2.
For a neutral molecule the formal charges add up to 0. For an ion, they add up to the total charge of the ion. This is a fast way to check your answer.
NEET asks it directly (like the O3 2026 question) and also uses it to justify why one Lewis structure or resonance form is better than another. Knowing FC helps in resonance, ozone, CO, SO2, and nitrogen oxide questions.
In carbon monoxide (C≡O), carbon has 1 lone pair and a triple bond: FC = 4 − 2 − 6/2 = −1. Oxygen has 1 lone pair and a triple bond: FC = 6 − 2 − 6/2 = +1. So carbon is −1 and oxygen is +1.
No. Because V, L, and S are whole numbers and S is always even for real Lewis structures, formal charge always comes out as a whole number (like −1, 0, +1, +2).
