Formal Charge + VSPER

What are polyatomic molecules?

Molecules made of 3/more atoms

What makes polyatomic and diatomic molecules different?

Polyatomic molecules have different possibilities for different shapes

• properties influenced by SHAPE

What does hypervalent mean?

Atoms/ molecules w/ more than 8 valence e- when in a covalent bond

What makes an element e- poor?

Less than 8 valence e- when in a covalent bond

What prediction can be made about molecules in terms of the valence e-?

If molecule has e- poor atom = VERY REACTIVE

What is formal charge (model)?

Most likely structure of polyatomic molecule is based on LOWEST FORMAL CHARGE

When CAN’T formal charge (model) be used?

If Lewis model can’t be used then this can’t be used

How is formal charge calculated?

#valence e- in free atom — #bonds to atom —#unshared e-

How does formal charge work when dealing with anions?

Lowest energy structure = most electronegative atom has the -/ve charge

What does VSPER stand for?

Valence shell e- pair repulsion

What is VSEPR used for?

Predicts shape of molecule

(NOTE: single bonds = σ bonds)

What assumptions are made to use VSEPR?

1. Atoms held by bonding pairs of e-

2. Atoms have lone pairs that AREN’T related to bonding

3. e- pairs repel (position as far apart from each other as possible)

4. Lone pairs need more room then bonding

5. Double/ triple bonds take up more space than single

How is the calculation carried out?

1. Calculate # vertices associated w/ central atom

• vertex = bonding/lone pairs

2. # vertices = # e- in σ bond + lone pair

How do double/triple bonds affect polyatomic molecules?

As double/triple bonds occupy more space than singles

• multiple bonds DISTORT shape of molecule AWAY from preferred geometry