Do Now & Announcements Complete notes (first page)—mostly review When done with first page, you may start the activities at the 3 stations You must use your observations and your knowledge of intermolecular forces to come up with the definitions in the boxes Unit 5 Test ~FRI 3/20

3. Intermolecular Forces Forces of attraction between molecules (dotted lines represents attraction between molecules)

http://phet.colorado.edu/en/simulation/states-of-matter

Intermolecular Forces & Phase of Matter For the same chemical substance, molecules in the SOLID phase will have stronger intermolecular forces between them than molecules in the GAS phase

Pressure: Atmospheric Pressure=pressure exerted by the air above a surface Vapor Pressure=pressure exerted by the molecules at the surface of the liquid; (they want to escape to the gas phase) VAPOR ATMOSPHERIC

VAPOR ATMOSPHERIC Boiling point of a liquid: vapor pressure = atmospheric pressure

: VAPOR PRESSURE = ATMOSPHERIC PRESSURE =NORMAL BOILING POINT - - - STANDARD ATMOSPHERIC PRESSURE also = 1 atm : VAPOR PRESSURE = ATMOSPHERIC PRESSURE =NORMAL BOILING POINT

Becoming a Gas (Add to Notes) A higher vapor pressure  will evaporate more easily and go into the gas phase For a liquid to boil, the vapor pressure (↑) must overcome the atmospheric pressure (↓) (the particles in the liquid phase are “breaking free” as they change into the gas phase!)

**If you live in Denver, Colorado, you often have to adjust cooking instructions. Why does water boil at a different temperature if you’re at a higher altitude (where the atmospheric pressure is lower)?