Intra-molecular Versus Inter-molecular Force

Intramolecular ForcesForces that hold compounds together

Ionic Transfer of electrons between a cation and

anionExample: saltsTypically solids at room temperature

CovalentSharing of electrons to achieve an octetBetween 2 or more nonmetalsCould be solids, liquids, or gases at room

temperature

Intermolecular ForcesThese are weak forces that exist

between moleculesVan der Waals ForcesLondon dispersion Dipole dipoleHydrogen bonding (strongest)

4th intermolecular force is an ion dipole force between an ionic compound and a polar compound (usually water)

States of Matter

Take time and talk with your table about properties and differences between a solid, liquid, and gas that have been discussed before today.

SolidsFixed and rigid arrangement and shape

Not compressible

Does not flow

Vibrational motion

Usually the most dense out of the three phases

Definite shape and volume

“High” intermolecular forces

LiquidsSlightly compressible

Takes the shape of the container

Intermolecular forces exist

More space between molecules

More motion

Takes the shape of the container with definite volume

Properties such as surface tension, viscosity, and adhesion/cohesion forces

Properties of water

https://www.youtube.com/watch?v=iOOvX0jmhJ4

Gases

No definite shape or volume

Highly compressible

Little to no IMF (follow the KMT)

High motion

States of Matter and IMF

The strength of the IMF will decide the state of matter of the substance.

For example, a large polar molecule sucrose C6H12O6 is a solid at room temperature while O2 is non-polar and a gas at room temperature

IMF and Properties

The higher the IMF, the higher theBoiling pointViscositySurface tensionCapillary actionhttps://www.youtube.com/watch?v=B

qQJPCdmIp8

Example

Below are the boiling points for 4 chemicals, compare and explain their respective BP.Water: 100 CSO2: -10 CNaCl: 1400 CCO2: -57 CHCl: 109 C

Classify phase changes as Exothermic or Endothermic

Heating Curves• Plot of temperature change versus heat

added is a heating curve.• During a phase change, adding heat

causes no temperature change.– These points are used to calculate Hfus and Hvap.

• Supercooling: When a liquid is cooled below its melting point and it still remains a liquid.

• Achieved by keeping the temperature low and increasing kinetic energy to break intermolecular forces.

Heat Curves

Vapor Pressure

Explaining Vapor Pressure on the Molecular Level

• Some of the molecules on the surface of a liquid have enough energy to escape the attraction of the bulk liquid.

• These molecules move into the gas phase.• As the number of molecules in the gas

phase increases, some of the gas phase molecules strike the surface and return to the liquid.

• After some time the pressure of the gas will be constant at the vapor pressure.

Gas-Liquid Equilibrium

Vapor Pressure

Volatility, Vapor Pressure, and Temperature

• If equilibrium is never established then the liquid evaporates.

• Volatile substances evaporate rapidly.• The higher the temperature, the higher

the average kinetic energy, the faster the liquid evaporates.

Vapor Pressure Graphs

Vapor Pressure and Boiling Point• Liquids boil when the external

pressure equals the vapor pressure.• Temperature of boiling point

increases as pressure increases.• Two ways to get a liquid to boil:

increase temperature or decrease pressure.

• Normal boiling point is the boiling point at 760 mmHg (1 atm).

How does a Pressure Cooker work?

Phase Diagrams• Phase diagram: plot of pressure vs.

Temperature summarizing all equilibria between phases.

• Given a temperature and pressure, phase diagrams tell us which phase will exist.

• Features of a phase diagram:– Triple point: temperature and pressure at

which all three phases are in equilibrium. – Vapor-pressure curve: generally as

pressure increases, temperature increases.

– Critical point: critical temperature and pressure for the gas.

– Melting point curve: as pressure increases, the solid phase is favored if the solid is more dense than the liquid.

– Normal melting point: melting point at 1 atm.

Phase Diagrams