CHEM320-lecture12-Simple Bonding Theory

VSEPR

considers mostly electrostatics in determining the geometry of the molecule

valence bond theory

considers quantum mechanics and hybridization of atomic orbitals

molecular orbital theory

upon bond formation, new orbitals that are linear combinations of the atomic orbitals are formed

Valence shell electron pair repulsion

aka VSEPR

theoretical tool to approximate the structures of molecules or ions

MINIMIZES the electrostatic repulsion between the regions of high electron density around a central atom

more

lone pairs take up ___ room than bonding pairs which can lead to bond angle compression relative to idealized version

Same can be said for multiple bonds compared to single bonds, as well as for larger atom compared to smaller ones.

shell expansion

elements that on occasion break the octet rule, usually stays on the right end of the periodic table, starting at the 3rd row.

Xn

bond charge cloud

Em

lone pair charge cloud

A

central atom in VSEPR notation

AX2

linear

180

AX3

trigonal planar

120

AX2E1

bent

120

AX4

tetrahedral

109.5

AX3E1

trigonal pyramidal

109.5

AX2E2

bent

109.5

AX5

trigonal bipyramidal

90 angle up and down

120 angle in same plane as central atom

AX4E1

seesaw

90 angle up and down

120 angle in same plane as central atom

AX3E2

T-shaped

90 angle up and down

120 angle in same plane as central atom

AX2E3

linear

90 angle up and down

120 angle in same plane as central atom BUT more like 180 between bonded atoms

AX6

octahedral

90 bond angle

AX5E

square pyramidal

90 bond angle

AX4E2

square planar

AX3E3

T-shped

AX2E4

linear

increases, decreases

atomic size ___ down a group and ___ across a period

electronegtaivity

measure of the ability of an atom in a molecule to attract electrons to itself

decreases down a group and increases across a period

polar

a ___ bond/molecule has a net dipole moment

molecules will be ___ if the bonds are __ and the molecule is NOT symmetric, aka the dipole moments do not cancel each other out

greater

the __ the difference in electronegativity between atoms, the more polar the bond