University11 min

Advanced Lewis: formal charges, resonance, hypervalence

Compute a formal charge, choose between two Lewis structures, put a number on a resonance bond order and recognise the three exceptions to the octet.

The essentials

1

Formal charge

FC=Nv−Nnb−Nb2\text{FC} = N_\text{v} - N_\text{nb} - \dfrac{N_\text{b}}{2} with NvN_\text{v} the valence electrons of the free atom, NnbN_\text{nb} its non-bonding electrons in the structure, NbN_\text{b} its bonding electrons. The formal charges add up to the charge of the species.
2

Choosing between two structures

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3

Resonance and bond order

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4

Hypervalence

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5

The three exceptions to the octet

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