Chapter 14 – Liquids and
Solids
14.1 Intermolecular Forces
Pgs 488 - 491
Objectives
• Review the difference between polar
and nonpolar molecules
• Identify the difference between
intermolecular forces and
intramolecular forces
• Distinguish between the three main
types of intermolecular forces
Let’s Review!!
• Draw the Lewis Dot structure for the
following molecules:
Cl2
HCl
H2O
Intermolecular Forces
• Most substances made of small
molecules are gases at normal
temperatures and pressures (25oC, 1atm)
– Oxygen gas (O2), nitrogen gas (N2),
methane gas (CH4) and carbon dioxide
(CO2)
– What about water (H2O)?
• Intermolecular forces hold water molecules
together to keep it a liquid!
– Intermolecular forces are the “forces” that occur
between molecules
Difference between Intermolecular
Forces and Intramoleulcar Forces
• INTRAmolecular forces occur WITHIN a
molecule
– Covalent and Ionic Bonds
• INTERmolecular forces occur BETWEEN
molecules
– 3 Types:
• Dipole – dipole attraction
• Hydrogen bonding
• London dispersion forces
Intramolecular Forces
Low
Strength of Intramolecular forces
High
Dipole-Dipole
Intermolecular Attraction
• = Intermolecular attraction between polar
molecules
F
Cl
F
Cl
Dipole-Dipole
Intermolecular Attraction
• = Intermolecular attraction between polar
molecules
F
Cl
F
Cl
F
Cl
Dipole-Dipole
Intermolecular Attraction
• = Intermolecular attraction between polar
molecules
F
Cl
F
Cl
F
Cl
Dipole – Dipole Attraction
• Dipole-dipole
attractions exist
between polar
molecules
Hydrogen Bonding
• Hydrogen bonds:
EXTREMELY strong
dipole attractions
– Occur when hydrogen
is bonded to F, O, or N
London Dispersion Forces
• London Dispersion Forces:“attractions”
that are found between nonpolar
molecules
– We know these forces exist because
noble gases are liquids and solids at low
temperatures!
London Dispersion Forces
• Occur when the
electrons around a
nonpolar atom arrange
themselves in a way to
create a temporary
dipole
London Dispersion Forces
• Once the dipole is formed, it can induce other
surrounding atoms to form dipoles as well
• As the size of the atoms increases, the London
Dispersion Forces become more significant