2.2.14 (HL)—Formal charge

$formal charge = valence electrons − non-bonding electrons − 1/2(bonding electrons)$

Calculate formal charges for each valid Lewis structure, then compare the charge distribution when choosing a preferred representation. Preserve the total charge of the species.

After calculating every atom, verify that formal charges sum to the overall species charge. Prefer a valid structure that minimizes charge magnitude and separation, placing negative formal charge on the more electronegative atom when other evidence is comparable; formal charge is bookkeeping, not measured partial charge.

Representative question

[Maximum number: 2]

Outline, in terms of formal charge, why Lewis formula 2 is preferred.

Retrieve the covalent pathway: shared pairs and bond order lead to geometry, polarity and molecular polarity; structure determines network properties, IMF behaviour and chromatography; HL representations extend to resonance, formal charge, sigma/pi bonds and hybridization.

Check the representation first, then count domains, apply geometry, identify polarity or forces, and connect the structure to the requested property or HL bonding description.

2.2.14 (HL)—Formal charge

Formal Charge and Lewis Structures

Choosing with Formal Charge

Assessment in practice

The Covalent Model Summary

Question 1