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Lewis structure

Lewis structure of O₃

18 valence electrons. One O=O double bond and one O-O single bond, with one lone pair on O. 2 resonance structures.

OOO
  • O
  • lone pair

O₃Ozone

Bent

AB₂E: 2 bond pairs, 1 lone pair on central O

  • Hybridisationsp²
  • Bond angleabout 117°
  • Polaritypolar

Lewis structure

18 valence electrons, 2 resonance structures
i

NCERT draws these two resonance structures; both O-O bonds are the same length.

OOO+−
OOO+−

Formal charges: O +1, O −1

Why this shape

  1. The central O has 6 valence electrons. In the Lewis structure it makes one double bond to O and one single bond to O and keeps one lone pair, which leaves it a formal charge of +1.
  2. Steric number = two sigma bonds + one lone pair = 3, so the central O is sp² hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.
  3. Three electron pairs point to the corners of a flat triangle (trigonal planar electron geometry). With one lone pair in place of atoms, the atoms make a bent shape.
  4. Repulsion falls in the order lone pair to lone pair > lone pair to bond pair > bond pair to bond pair. The lone pair pushes the bond pairs closer, so the angle is about 117°, less than the ideal 120°.
  5. All three atoms are O, but the central O carries a different charge from the end ones and the molecule is bent, so it has a small dipole moment.
Working

How to draw it

  1. Count the valence electrons: 3 × O 6 = 18 valence electrons, 9 pairs.
  2. Put O in the middle and join it to the two outer atoms with single bonds.
  3. Give each outer atom lone pairs until it has an octet (H needs only two electrons), then put any electrons left over on the central atom.
  4. Where an atom is still short of an octet, turn a lone pair of its neighbour into a shared pair: that makes a double or triple bond.
  5. Result: one O=O double bond and one O-O single bond, with one lone pair on O.
  6. Formal charge = valence electrons − lone pair electrons − number of bonds. Here: O +1, O −1.
  7. The double bond can sit in two equivalent ways, so there are two resonance structures. The real molecule is a hybrid of them.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

Lewis structure of O3: quick answers

How many valence electrons are in O3?

3 × O 6 = 18 valence electrons, 9 pairs.

What are the formal charges in the Lewis structure of O3?

O +1, O −1; every other atom is zero. Formal charge = valence electrons - lone pair electrons - number of bonds.

How many resonance structures does O3 have?

2. The double bond can sit in two equivalent ways, so there are two resonance structures. The real molecule is a hybrid of them.

Try any molecule