FC, Resonance & Lewis Structures

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Formal Charge

the hypothetical charge on a bonded atom within a structure, that determines how “good” & accurate a structure is. Formal charge is calculated for one singular atom!

Formal Charge Formula

FC = (#valence e- regularly) - (#unbonded e-) - 1/2(#bonded e-)

The Best Formal Charge is

the smaller/closer to zero

Formal Charge for the entire atom is calculated by

summing the different formal charges together.

Resonance

different variation of a single compound where formal charge differs, but these structures are the same and valid.

Resonance Hybrid

The actual molecule that shows the different the different resonance structures all combined. With dashed lines where the different bonds are.

What resonate structure contributes the most to the resonance hybrid

the resonance structure with the lowest formal charge.

Line with arrows on both sides is used for

Resonance structures

Odd electron species must have 1 unpaired electron so..

the break the octet rules, eg NO

Radical Molecules

A molecule with an unpaired e, making ti very reactive.

Boron and Beryllium break,

the octet rule, by not completing it, being electron deficient and in turn very reactive.

Expanded Octets

When an atom breaks the octet rule by having more than 8 electrons

Expanded Octets Happen When

The atom is able to use D orbitals ie (period 3 and lower)

When writing Lewis Structures satisfy octets first,

then place electrons around elements having d orbitals at their disposal.

Extra electrons in a Lewis Structure

go on the atom with d orbital savable OR likely the central atom

The Steps For Drawing Lewis Structures

1. Indeitfy the number of valence electrons and extra electrons

2. Identify the central atom

3. Draw the atom with all octets filled

4. Add bonds or extra pairs as needed.