Intramolecular Forces

vsIntermolecular

Forces

Intramolecular ForcesThere are 2 types of attraction in molecules: intramolecular bonds & intermolecular forces

• We have already looked at intramolecular bonds– These are forces that hold atoms together to form

molecules– Examples: Ionic, Non-Polar Covalent, and Polar

Covalent

Intermolecular Forces • Intermolecular forces (IMF) have to

do with the attraction between molecules

There are 3 different levels of strength in IMFs- Hydrogen bonding (the strongest)- Dipole-dipole Forces- London Dispersion Forces (the weakest)

POLAR

NON-POLAR

H-bonds & Dipole-DipoleRemember: POLAR BEARS DON’T SHARE FAIR

• The unequal sharing in polar bonds cause a slight (+) charge on one atom, and a slight (-) charge on the other atom

Dipole-Dipole

So what’s a H-bond?• H-bonding is a special type of dipole -

dipole attraction that is very strong• It occurs when N, O, or F are

bonded to H

Bonding Is

FHON!

Hydrogen bondsWhat do you need?

A hydrogen atom covalently bonded to an electronegative atom … N, O or F.

If only one of these conditions is met, you don’t get H-bonds

A lone pair of electrons on the electronegative atom.

Polar Covalent bond

London Dispersion Forcesaka “van der Waal” forces• Seen in non-polar molecules• Happen because partial charges can show up

for just an instant (b/c e-s are moving)• This creates a temporary dipole– When e- leaves, the dipole is gone

REMEMBER • All bonds are stronger than all intermolecular

forces. • Molecules that use bonding only will have the

strongest structures • Molecules that use bonding and intermolecular

forces will have weaker structures, where the strength depends upon the type of intermolecular force used

• Molecules that use intermolecular forces and no bonding will have the weakest structures known; examples of these would be Noble Gases.

REFLECTION:•On the LEFT side of your

notes:–List the different types of bonds•STRONGEST on top•WEAKEST on bottom