Intermolecular Forces https://www.youtube.com/watch?v=KFPvdNbftOY

Intermolecular forces are attractive forces among molecules. (Example: water molecule to water molecule) Intramolecular forces hold atoms together within in a molecule. (Example: H to O bond within a water molecule). Generally, intermolecular forces are much weaker than intramolecular forces. “Measure” of intermolecular force boiling point melting mpoint Hvap Hfus 11.2

Intermolecular Forces 1. London Forces (a.k.a. Dispersion Forces) AKA Van Der Waals Forces Weakest Dipole-Dipole Interactions Ion-Molecule Interactions -(Salt dissolving in solution; Na+ and Cl- ) 4. Hydrogen Bonding (STRONGEST)

London Dispersion (Van Der Waals) Forces Weakest Occur between nonpolar molecules and arise from the net attractive forces among molecules which are produced from temporary charge imbalances The larger the molecule the greater it’s Dispersion Forces are.

Is the Molecule Polar? The more Electronegative atom will pull the electron density of the bond Closer to itself giving it a partial negative charge leaving the other Atom with a partially positive charge. This is a dipole moment.

Which of the following molecules are polar (have a dipole moment)?H2O, CO2, SO2, and CH4 O H S O dipole moment polar molecule dipole moment polar molecule C H C O no dipole moment nonpolar molecule no dipole moment nonpolar molecule 10.2

Orientation of Polar Molecules in a Solid Dipole-Dipole Forces Attractive forces between polar molecules Orientation of Polar Molecules in a Solid 11.2

Ion-Molecule attraction Attractive forces between an ion and a polar molecule Ion-Molecule Interaction The larger the charge the stronger the force 11.2

A molecular picture showing the ion-dipole Olmsted Williams Fig 10-34 A molecular picture showing the ion-dipole Interaction that helps a solid ionic crystal dissolve in water. The arrows indicate ion-dipole interactions.

What type(s) of intermolecular forces exist between each of the following molecules? HBr HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules. CH4 CH4 is nonpolar: dispersion forces. CO2 CO2 is a nonpolar molecule:Van Der Waals. 11.2

The Hydrogen Bond STRONGEST INTERMOLECULAR FORCE

water has the highest heat of fusion water has the highest melting point water has the highest boiling point water has the highest heat of vaporization water has the lowest molar mass The melting point, boiling point, heat of fusion and heat of vaporization of water are extremely high and do not fit the trend of properties relative to molar mass within Group 16.

Water exhibits these unusual properties because of hydrogen bonding between water molecules.

A hydrogen bond is an intermolecular force formed between polar molecules that contain hydrogen covalently bonded to a small, highly electronegative atom: F, O, N. F—H O—H N—H

The H of one molecule will be attracted to another F, O, or N, on another molecule. A dipole-dipole bond will be formed between the two molecules which is called a hydrogen bond. hydrogen bond covalent bond covalent bond

Water in the liquid and solid states exists as groups in which the water molecules are linked together by hydrogen bonds. 13.8