Intra-molecular Versus Inter-molecular Force

Intramolecular Forces Forces that hold compounds together Ionic Transfer of electrons between a cation and anion Example: salts Typically solids at room temperature Covalent Sharing of electrons to achieve an octet Between 2 or more nonmetals Could be solids, liquids, or gases at room temperature

Intermolecular Forces These are weak forces that exist between molecules Van der Waals Forces London dispersion Dipole dipole Hydrogen bonding (strongest) 4 th 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.

Solids Fixed 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

Liquids Slightly 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 ?v=iOOvX0jmhJ4 ?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 C 6 H 12 O 6 is a solid at room temperature while O 2 is non-polar and a gas at room temperature

IMF and Properties The higher the IMF, the higher the Boiling point Viscosity Surface tension Capillary action PCdmIp8 PCdmIp8

Example Below are the boiling points for 4 chemicals, compare and explain their respective BP. Water: 100 C SO 2 : -10 C NaCl: 1400 C CO 2: -57 C HCl: 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  H fus and  H vap. 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 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 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 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