Splatter Test Lab

An introduction to intermolecular forces

INTER vs INTRA

Forces

Intermolecular Forces

Hydrogen Bonding Dipole-Dipole

London Dispersion

Forces

Intramolecular Forces

Covalent Ionic

INTRAMOLECULAR forces are stronger than INTERMOLECULAR forces.

INTERMOLECULAR forces

• Force of Attraction between a Hydrogen atom of one molecule and an N, O, or F of another of the same molecule. VERY STRONG!! Found in Water!

Hydrogen Bonding

• Found in polar molecules because of the DIPOLE (uneven distribution of charge >0.4 electronegativity difference). Polar molecules dissolve other polar molecules. Strong!

Dipole-

• Found in non polar and polar substances alike. This is an instantaneous DIPOLE that occurs because atoms are moving around. VERY WEAK!!!

London Dispersion Forces

STRONGEST > WEAKEST: Hydrogen bonding> Dipole> London dispersion forces.

Examples of Each Type

• Examples: Water, H2O, NH3, HF, H2O2, alcohols (H of one compound and O,N,F of another)

Hydrogen Bonding

• Examples: CH3Cl, SCl2, PCl3, H2O, NH3, HF, H2O2, alcohols, polar compounds

Dipole-

• H2, Cl2, CO2, N2O4, CH4, paraffin wax, polar and non polar substances!

London Dispersion Forces

NEW WORD!!!

• Volatile- Volatile is how easily a substance evaporates. – High volatility-Evaporates very fast.– Low volatility-Evaporates slowly.

– Can you smell all substances that have evaporated?

• Smell– In order to smell something, the aroma (esters, chemicals) must

reach your nose and you must have the receptors to interpret that smell.

Procedure

• Procedure:• 1. Place a penny face down on a weighing boat.• 2. CAREFULLY add drops of water on top (pipet

straight up and down). Your goal is to put as many drops on top of the penny without any water falling into the weighing boat.

• 3. Count the number of drops that the penny was able to HOLD. RECORD.

Procedure

• 4. Dry the penny with a paper towel. Place the water in the sink.

• 5. Repeat the process. Record.• 6. Repeat procedures using isopropyl alcohol.

You can put the isopropyl alcohol down the sink as well.

• 7. Repeat procedures using acetone. Place the “waste” acetone in the “waste container” (with a lid).

• Conclusions– Hydrogen bonding is the strongest type of

intermolecular force.– A non polar molecule can only have london dispersion

forces.– A polar molecule can have london dispersion forces,

and dipole forces.– Certain polar molecules like water and ammonia can

have london dispersion forces, dipole forces, and hydrogen bonding.

– The stronger the intermolecular force, the LESS volatile a substance is.

– The weaker the intermolecular force, the MORE volatile a substance is.

– You don’t always smell volatile substances!!!!!