Intermolecular Forces Unit 3: Bonding Intermolecular Forces

Polarity and Solubility “like dissolves like” How do we explain this???

Intermolecular Forces Intermolecular forces: weak and mostly temporary attractions between molecules Need to know: London dispersion forces (induced dipole) Dipole-dipole forces Hydrogen bonding forces Ion-dipole forces

London Dispersion Forces London Dispersion forces attract nonpolar molecules or atoms by temporary induced dipoles due to uneven electron distribution Image from: http://www.chem.purdue.edu/gchelp/liquids/disperse.html

Dipole-Dipole Forces Dipole-dipole forces attract polar molecules to one another Image from http://www.teachmetuition.co.uk/Chemistry/Intermolecular/dipole.htm

Hydrogen Bonding Forces Hydrogen Bonds: an interaction between a hydrogen and an O, N, or F atom (note that they are very electronegative atoms). H-bonds raise boiling points Right image from: http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/page3.html Left image from: http://www.science.uwaterloo.ca/~cchieh/cact/c123/intermol.html

Ion-Dipole Forces Ion-Dipole forces attract an ion (+ or -) to a polar molecule Example: Na+ and Cl- ions aligning themselves with dipoles of water molecule Animation: http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/thermochem/solutionSalt.html Image from: http://www.science.uwaterloo.ca/~cchieh/cact/c123/intermol.html

Relative Strengths of Intermolecular Forces London dispersion forces

Other Bond-Like Forces A nice summary of intermolecular forces: http://www.wisc-online.com/objects/index_tj.asp?objID=GCH6804