Unit 3: IMFs AP CHEMISTRY

INTERMOLECULAR FORCE

attraction between molecules

-IMF

MUCH WEAKER THAN INTRAMOLECULAR

INTRAMOLECULAR

Attraction within a molecule

-Covalent bond

MUCH STRONGER THAN INTERMOLECULAR

Why is boiling point the best measure of IMFs

When substance boils or turns to gas, ALL IMFs have been severed. This severing of the IMFs process allows the single molecule of H2O to escape from the rest of the sample and float into atmopshere

Ion-dipole

Attraction between ion and polar molecule

Ranking IMFs

LDFS < Dip-Dip < Hydrogen Bonding < Ion-Dip

Ion-Dipole: Forces of attraction increase as…

CHARGE OF ION INCREASES
RADIUS OF ION DECREASE
MAGNITUDE OF THE DIPOLE ON POLAR MOLECULE INCREASES

Dipole-Dipole

Attractive forces between the more negative end of one polar molecule and the more positive end of another polar molecule or same molecule

_____ and ______ dipoles line up (IN DIP-DIP)

positive, negative

NON-POLAR MOLECULES

less orderly due to less attraction

Hydrogen

Dipole-Dipole attraction

REQUIREMENTS TO BE A HYDROGEN BOND

1. H covalently bonded to F, O, or N

2. F, O, or N on another molecules with at least 1 lone pair

Why is H Bonding so Strong?

When H is bonded to an F, O, or N, the H becomes very positive due the F,O, or N being extremely electronegative. This positive H is then very attracted to a negative nearby F, O, or N with a lone pair

Dipole-Induced Dipole Attractions are stronger when:

• polar molecule has a large dipole moment

• the non-polar molecule has a larger electron cloud (more polarizable)

LDFS

-All species (even neutral atoms) have LDFs

-Due to temporary skewing of electron cloud

-Instantaneous charge distributions are polar

Polarizability

The more electrons a species has, the stronger LDF’s — the electron cloud is more POLARIZABLE

LDFs increase as the ________ between molecules increasdes

contact area