Homework

Read pages 462 – 466Answer questions p 466

#21, 22, 23, 24, 26

Intermolecular force of attraction

• Def: forces that hold molecules together, through an electric attraction- typically the positive end of one molecule is attracted to the negative end of another molecule- we see the effect of intermolecular forces of attraction in the state of matter of a particular substance

Boiling points

• Boiling points of different substances can act an indirect measure of the attractive forces between molecules. - as the molecules of a substance are separated from a liquid to a gas, the forces of attraction must be overcome between the molecules- the stronger the forces of attraction between the molecules, the more energy is required to change phase, therefore higher the boiling point

- the intermolecular forces are due to attraction between opposite ends of the molecules, therefore the more polar the molecule, the stronger the positive and the negative ends of the molecules and the stronger the force of attraction between them

Types of IMFDipole-Dipole Attractions

Def: force of attraction between the positive end of one dipole, and the negative end of a neighboring dipole

the greater the degree of polarity within the molecules, the stronger the dipole – dipole attraction

Hydrogen Bonding

– very strong form of dipole - dipole attraction between molecules that are small and very polar.

- when hydrogen bond to strongly electronegative elements (N, O, F) a very polar bond is formedthe H is left with a strong partial positive charge

- the positive (H) side of the molecule is strongly attracted to the unshared pairs of electrons on the N, O, or F atom.Ex) NH3, H2O, and HF

- the boiling points of these substances are much higher than

expected due to the strength of the H bonding.

London Dispersion Forces

- formation of a momentary dipoles as the result of the repulsion of electrons from neighboring atoms

- Very weak IMF- Only acts over a very short range- The larger the molecule, the stronger the

dispersion forces between the molecules

Molecule Ion attraction

- The attraction between polar molecules and ions, the oppositely charges sides of dipoles attract oppositely charged ions.

- Responsible for dissolving