AP Chemistry Unit 3.1 Review

intramolecular force

force within a molecule

intermolecular force

force between molecules

what happens when you boil water?

you break the connections between individual water molecules

intermolecular forces are what?

Coulombic forces

what is the key for any intermolecular connection?

• and -

Dipole - Dipole Interactions

polar + polar

what factor affects the strength of the dipole-dipole interaction?

increase in polarity which would lead to a larger dipole moment

Dipole-Induced Dipole

polar + nonpolar

-the presence of the polar molecule created a dipole

-the induced dipole on the nonpolar molecule is temporary

and forced by the interaction with the polar molecule

London Dispersion Forces

nonpolar + nonpolar

-sometimes molceules stick together without a charge

key notes about intermolecular forces

-ALL intermolecular connections include LDF

-LDF are the primary type of interaction between nonpolar molecules

-the strength of the LDF depends on how easily the electron clouds can disperse

key phrase to know

the larger the electron cloud

Hydrogen "Bonding"

hydrogen + F

Ion - Dipole

ion + polar

why are sometimes boiling points different?

the greater surface area of molecules allows for more interaction

the higher heat of vaporization for Cl₂ indicates that it has stronger intermolecular forces than HCl. explain.

the electron cloud for chlorine is big enough that it creates a stronger force than HCl

why are the boiling points different between olive oil and propane?

olive oil's surface area is much bigger

what are the properties that can be explained by intermolecular forces?

1. Melting/Boiling Point, Vapor Pressure, Volatility, Surface Tension, Viscosity, Heat of Vaporization

Melting/Boiling Point

more energy is needed for a stronger IMF temperature

Vapor Pressure

pressure exerted by a gas when it is at equilibrium with its liquid

-low vapor pressure

strong IMF lead to high resistance for molecules to escape the liquid

-high vapor pressure

weak IMF

Volatility

ease of vaporization

-weaker IMF

easier to evaporate

Surface Tension

high surface tension

Viscosity

resistance to flow

-higher viscosity

higher IMF

Heat of Vaporization

energy required to evaporate a substance

comparing the strength of intermolecular forces

if size of the molecule is similar - hydrogen bonding > dipole-dipole > LDF

if the molecules vary in size

comparison becomes difficult

based on data

how can we judge the relative strength of the intermolecular forces?