Lecture 6: The Shape of Molecules

Valence Shell Electron Repulsion Theory:

Electrons repel each other due to their negative charge, creating the shape of 3D molecules

Steric Number (SN)

The number of electron groups around an atom

Steric Number includes what kinds of electron groups?

Both unpaired and bonded electrons

For the steric number, each electron group is counted how many times?

once

The three steps of VESPR theory:

Draw the electron dot diagram, find the steric number for the atom, predict the maximum angle

For a steric number of two, the maximum angle between electron groups is

180°

For a steric number of three, the maximum angle between electron groups is

120°

For a steric number of four, the maximum angle between electron groups is

109.5°

Molecular shape

The shape of a molecule, which does not include lone pairs of electrons

Molecular geometrical arrangment

The shape a molecule would have if lone pairs of electrons were included

Tetrahedral Molecular Shape

Four bonding groups

Trigonal Planar Molecular Shape

Three bonding groups

Linear Molecular Shape

Two bonding groups

Pyramidal Molecular Shape

Three bonding groups, one lone pair

Bent Molecular Shape

Two bonding groups, one or two lone pairs

Intermolecular forces

Electrostatic forces that hold neighboring molecules together

Intermolecular forces are determined by

Molecular shape

Dipoles

When a molecule has multiple polar covalent bonds, which do not cancel each other out

Dipole-Dipole forces

When dipolar molecules are attracted to each other due to their charge