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 Explain that we are going to make the nonpolar to polar separation separated again and more precise Today we are only talking about intermolecular forces for molecular compounds (Which have a smaller intermolecular force of attraction than ionic compounds) Add polar covalent and nonpolar covalent to this and then highlight the covalent region to show that we will be defining this area more! (To add intermolecular forces and how that relates to melpting point)

Dipole-Dipole Intermolecular Attraction = Intermolecular attraction between polar molecules F Cl dipole-dipole attractions are about 1% the strength of a covalent bond. When the neg end of a polar molecule is attracted to the pos. end of another rmolecule F Cl

Dipole-Dipole Intermolecular Attraction = Intermolecular attraction between polar molecules F Cl dipole-dipole attractions are about 1% the strength of a covalent bond. F Cl F Cl

Dipole-Dipole Intermolecular Attraction = Intermolecular attraction between polar molecules F Cl dipole-dipole attractions are about 1% the strength of a covalent bond. F Cl F Cl F Cl F Cl F Cl

Dipole – Dipole Attraction Dipole-dipole attractions exist between polar molecules The positive and negative ends of the molecule are attracted to each other In liquids, the dipoles find the best orientation to maximize the attractions and minimize the repulsions Only 1% as strong as covalent or ionic bonds They become weaker as the distance between the dipoles increases In gases, the molecules are so far apart the dipole attractions are basically non-existent

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 The motion of the atoms must be greatly slowed in order to create solids