Chapter 14 – Liquids and Solids 14.1 Intermolecular Forces Pgs 488 - 491
Dec 29, 2015
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