Intermolecular Attractions Chemical BONDING Intermolecular Attractions

Intermolecular attractions Attractions between molecules 1. London Dispersion Forces Weak attractive forces between non-polar molecules Ex. CH4, CO2 & Halogen molecules Strongest LDF between molecules with LOTS of electrons.

Rank in order of weak to strong L-D F2, I2, Br2, Cl2 H2, CH4, CCl4 I2, CF4, CO2

2. Dipole-dipole attractions Stronger attractions that occur between polar molecules (still only 1% of the strength of a covalent bond) Hydrogen “Bonding” Special type of dipole-dipole force found ONLY between FH - - - - F OH - - - - O NH - - - - N

Why does H “bonding” occur with only these 3 atoms? Nitrogen, Oxygen and Fluorine 3 highest electronegativities smallest atoms with strongest nuclear charges

H “bond” H F

Intermolecular forces determine the properties (behavior) of the substance Stronger IMFs, result in higher boiling points, higher melting points and slower evaporation of substances.

The Unusual Properties of Water Unusually high boiling point compared to other Hydride compounds in Group 16. Explain why.

Rank these substances from highest to lowest boiling point NaCl I2 H2O H2 H2S

H2O Hydrogen bonding IMF NaCl Ionic bonding H2O Hydrogen bonding IMF H2S dipole-dipole IMF not as strong as H bonds I2 stronger LDF larger e- cloud than H2 H2 weakest LDF smallest e- cloud Lowest Highest

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