Chapter 14 – Liquids and Solids

14.1 Intermolecular ForcesPgs 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 HClH2O

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

Strength of Intramolecular forces HighLow

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

F C

l F C

l F C

l

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