How to Draw the Lewis Structure for ClO3⁻ with All Resonance Forms, Formal Charge, Polarity, and Molecular Geometry

To draw the Lewis structure for ClO₃^– (chlorate ion), follow these steps:

1. Count the total number of valence electrons:
   • Chlorine (Cl) has 7 valence electrons.
   • Each Oxygen (O) has 6 valence electrons.
   • There are 3 Oxygen atoms, so 3 × 6 = 18 electrons.
   • Add 1 electron for the negative charge.
   • Total valence electrons = 7 + 18 + 1 = 26 electrons.
2. Place the least electronegative atom in the center:
   • Chlorine (Cl) is less electronegative than Oxygen (O), so Cl is the central atom.
3. Connect the central atom to the surrounding atoms with single bonds:
   • Draw single bonds between Cl and each O atom.
   • This uses 6 electrons (3 bonds × 2 electrons).
4. Distribute the remaining electrons:
   • Subtract the used electrons from the total: 26 – 6 = 20 electrons.
   • Place lone pairs on the Oxygen atoms to satisfy the octet rule.
   • Each O atom needs 6 more electrons (2 lone pairs).
   • This uses 18 electrons (3 O atoms × 6 electrons).
   • Remaining electrons: 20 – 18 = 2 electrons.
   • Place the remaining 2 electrons on the central Cl atom.
5. Check for octet rule compliance:
   • Cl has 8 electrons (2 from the lone pair and 6 from the bonds).
   • Each O atom has 8 electrons (6 from lone pairs and 2 from the bond).
6. Draw resonance structures:
   • Move lone pairs from O atoms to form double bonds with Cl.
   • This creates multiple resonance structures where the double bond can be with any of the 3 O atoms.
7. Calculate formal charges:
   • Formal charge = Valence electrons – (Non-bonding electrons + ½ Bonding electrons).
   • For Cl: 7 – (2 + ½ × 6) = 0.
   • For each O with a single bond: 6 – (6 + ½ × 2) = -1.
   • For the O with a double bond: 6 – (4 + ½ × 4) = 0.
8. Determine polarity:
   • The molecule is polar due to the asymmetrical distribution of electron density and the presence of lone pairs on O atoms.
9. Determine molecular geometry:
   • The electron geometry is tetrahedral.
   • The molecular geometry is trigonal pyramidal due to the lone pair on Cl.

In summary, the Lewis structure for ClO₃^– has multiple resonance forms, a formal charge of 0 on Cl and -1 on the single-bonded O atoms, is polar, and has a trigonal pyramidal molecular geometry.