Unit 2 Summary
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Molecular bonding:
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London dispersion (Van der Waals)- nonpolar atoms/molecules have instantaneous dipole moments that can induce a
similar temporary dipole on an adjacent atom. Found in all substances. Increase with molecular weight and shape.
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Dipole-dipole (Van der Waals)- neutral polar molecules attract each other when the positive end of one molecule is near
the negative end of another. Increases with polarity.
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Hydrogen bonds- a special type of dipole-dipole between a hydrogen atom and a nonbonding electron pair on a nearby
small electronegative ion/atom (Nitrogen, Oxygen, Fluorine)
Ionic Structures:

Unit cell / crystal cubic structure / lattice – repeating, alternating arrangement of a solid with a 3D array of points.
Represents a crystalline solid
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3 types:
o
Simple Cubic: 1 atom, V = 8r3
o
Body-centered: 2 atoms, V = (4r/√3)3
o
Face-centered: 4 atoms, V = (4r/√2)3
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To count atoms: center=1, face= ½, edge = ¼, corner = 1/8
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Density = m/v = g/e3
Solubility
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This is the amount of a substance that can be dissolved in a given quantity of a solvent at a given temp, in g/L (see
solubility rules – Appendix A-8)
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Saturated- solution is in equilibrium with undissolved solute so additional solute won’t dissolve
Unsaturated- can dissolve more solute
Supersaturated- contains more solute than needed to form a saturated solution, unstable, any agitation can initiate
precipitates
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Henry’s Law- Sg = kHPg
The solubility of a gas increases in direct proportion to its partial pressure above the solution
Equilibrium
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This occurs when opposing reactions proceed at equal rates and have constant concentrations, so the reaction appears to
have stopped
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K is the equilibrium constant. Q is the reaction quotient
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Kc = [products]n
Kp = PCcPDd

Kc = Kp(RT)-Δn
[reactants]m
PAaPBb
Kp = Kc(RT)Δn

Ksp- solubility product constant, the equilibrium constant for the equilibrium between and ionic solid and its saturated
solution. This indicates how soluble a solid is in water
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LeChâtlier’s Principle- If a system at equilibrium is disturbed by a change in temp, pressure, or concentration, the system
will shift its equilibrium position so as to counteract the effect of the disturbance
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Molality = moles solute
kg solvent
Phase Changes
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Vapor pressure- constant production of liquid into gas and vice versa at equilibrium. This is higher with weaker IMFAs
because more molecules can overcome the attractive forces of their neighbors and escape into the gas phase. It is also
higher at high temps which gives them sufficient kinetic energy to escape

Volatile- evaporate readily, have high vapor pressure and temp
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When Pvap = Patm, the substance starts to boil. Decreasing the vapor pressure increases the boiling point
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Phase diagrams- show the conditions of temp and pressure at which states of matter exist at equilibrium
o
T- triple point, at which all 3 phases are at equilibrium
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C- critical point, the critical temp (highest temp at which a distinct liquid phase can exist) and critical pressure
(pressure required to bring about liquefaction at this temp)
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SCF- supercritical fluid, liquid and gas phases are indistinguishable from each other
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Colligative properties- depend on the concentration but not the identity of the solute particles. “i” is the Van’t Hoff factor,
the number of particles the solution dissociates into (real “i” is lower than ideal “i” because of ion pairings, IMFAs, and
other clusterings)
o
Lowering the vapor pressure
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adding a nonvolatile solute to a solvent always lowers the vapor pressure and therefore raises the
boiling point

Raoult’s Law: PA = χAP°A
(partial pressure exerted by solvent = mole fraction of solvent times the vapor pressure of the pure
solvent)
o
Osmotic pressure

This is the pressure required to prevent osmosis by pure solvent toward solution with the higher
solute concentration
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Π = MRT, units are atm
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Boiling Point of Elevation
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Ions hinder molecules from vaporizing, so it takes a lot more energy for it to boil

ΔTb = ikbm
o
Freezing Point of Depression
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Ions physically hinder water molecules from creating and orderly crystalline arrangement
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ΔTf = ikfm