Intermolecular attractions

Polarity and Shape Polar bonds do not necessarily always create a polar molecule. The shape of the molecule and the polarity of each bond is considered before stating if a molecule is considered POLAR or NON-POLAR http://www.mhhe.com/physsci/chemistry/chang7/esp/folder_structure/bo/m4/s2/index.htm

Non-polar Molecules A non-polar molecule is one that the electrons are distributed more symmetrically and thus does not have an abundance of charges at the opposite sides. The charges all cancel out each other.

Are the following polar or non-polar MOLECULES?

Homework: Read pages 250-251 Take notes on Van der Waals forces (dipole interactions and dispersion forces) and hydrogen bonds. (at least two sentences to explain each.) Complete questions 32 and 34 on page 253 This assignment is to be hand in tomorrow

Intermolecular Forces Forces binding atoms in a molecule are due to chemical bonding Intramolecular forces: forces that bond the atoms to each other within the molecule. Vs Intermolecular forces:

Dipole-Dipole Forces Dipole = polar molecule Dipoles will change their direction so that their oppositely charged ends are near to one another. The electrostatic attraction between the ends is dipole-dipole force

Ion Dipole Forces The force of attraction between an ion and a polar molecule. NaCl breaks up because the ion dipole with water is stronger than the attraction of Na+ to Cl-

Dispersion Forces weakest intermolecular force between non polar molecules It is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles

Hydrogen Bonding It is the attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. The molecule involved with hydrogen bonding should have at least one lone pair. More lone pairs= stronger hydrogen bonds.

“Like Dissolves Like” Ionic solutes dissolve in polar solvents (ex: NaCl and H2O) Non polar solutes dissolve in non polar solvents (ex: solid I2 and liquid Br2)