Intramolecular Forces vs Intermolecular Forces

Intramolecular Forces There 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-Dipole Remember: 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? It occurs when N, O, or F are bonded to H 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 bonds What do you need? A hydrogen atom covalently bonded to an electronegative atom … N, O or F. A lone pair of electrons on the electronegative atom. If only one of these conditions is met, you don’t get H-bonds

Polar Covalent bond

London Dispersion Forces aka “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