Jenna Mandel and Shela Wu AP Chemistry - 7

Intermolecular Intramolecular VS BETWEEN MOLECULESKEEPS MOLECULE TOGETHER When something undergoes a phase change, the changes occur in the intermolecular forces.

Occurs between two polar molecules HYDROGEN BONDING Strong form of dipole-dipole attractions Occurs in molecules with hydrogen that is bonded with an element with a high E.N. High difference in electronegativity & small size contributes to its great strength

L o n d o n D i s p e r s i o n F o r c e s OCCURS BETWEEN 2 NON-POLAR MOLECULES INSTANT- ANEOUS DIPOLES IN LARGE ATOMS, CAN BE MORE SIGNIFICANT THAN DIPOLE- DIPOLE FORCES

measure of liquid’s resistance to flow surface tension the resistance of a liquid to an increase in its surface area capillary action spontaneous rising of a liquid in a narrow tube a result of adhesion and cohesion Concave shape of meniscus shows adhesive > cohesive Viscosity: adhesive versus cohesive liquid particles attracted to themselves force between liquid and surrounding

describes the locations of the pieces in a crystalline solid LATTICE UNIT CELL smallest repeating unit of the lattice as apposed to amorphous solids…

ions at lattice points

small molecules at lattice points

atoms at lattice points Metallic Solids Positively charged & held together by neutrons. Delocalized electron sea theory

atoms at lattice points Network Solids Atoms bond covalently in a continuous network. Strong Bonds -> High mp & bp Do not conduct electricity

atoms at lattice points Group 8A Solids Noble gases bonded with London Dispersion Forces Occur at very low temperatures!

It’s ductile! It’s malleable! strong & nondirectional ELECTRON SEA MODEL metal cations in valence e - conduct heat and electricity malleable and ductile

VERSUS Hardest naturally occurring substance sp 3 hybridization large gap between filled and empty levels in energy diagram carbon surrounded by a tetrahedral Slippery, black, & a conductor Layers of carbon atoms in 6 member rings sp 2 hybridization weak bonding between layers accounts for slippery texture

PHASE CHANGES Heat of Vaporization ENERGY NEEDED TO VAPORIZE A MOLE OF LIQUID When does a liquid boil? its vapor pressure EQUALS pressure of the environment

ΔH vap = enthalpy of vaporization R = J/K·mol T = temperature (kelvin) C=constant Determine heat of vaporization, and can also be used to find P vap

Rate of evaporation remains constant while rate of condensation increases as number of molecules in vapor phase increases, until they become equal, and thus reach equilibrium.