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λ, ν, c, h
- λ = Wavelength - distance between successive crests (cm, m, nm)
- ν = Frequency - number of cycles in a given amount of time (1/s = Hz)
- c = Speed of Light - 3.00x108m/s
- h = Planck's constant - 6.626x10-34J·s
- E = (constant) x q1q2/r
- q = charge of ions
- r = size of atom
- Amount of energy required to separate a molecule from the liquid (boil)
- ΔHvap increase = stronger intermolecular forces
- Larger surface area = faster rate of evaporation
- Pressure in a closed container from molecules that have vaprorized from liquid within (they can't escape, so they create pressure)
- Higher vapor pressure = weaker intermolecular forces (more easily vaporized = more molecules in air = more vapor pressure)
- Resistance of liquid to flow
- 1 poise = 1P = 1g/cm x seconds
- H2O is 1 cP at room temperature
- Larger viscosity = larger intermolecular forces
- more spherical molecular shape = decreased viscosity (less surface to surface contact)
- increased temperature = decreased viscosity (increase to average kinetic energy, easier to overcome flow)
- Regions represent states, lines represent state changes
- Critical point: the furthest point on a vapor pressure curve
- Triple point: temperature/pressure where all 3 states exist simulatenously
- Normal BP, FP, etc = pressure @ 1 atm.
- Substances past the critical point on a phase diagram
- State that has some liquid properties and some gas properties
- Made from sealed liquid being heated, increased pressure, increased vapor density, decreased liquid density... essentially they all merge.
- S = solubility, KH = Henry's Law constant (different for each gas), P = pressure
- As pressure increases, gas solubility increases
- As pressure decreases, gas solubility decreases
- Psolvent in sol=Xsolvent x P0
- P = pressure, X = mole fraction, P0 = pressure of pure solvent
- Vapor pressure calculation
Boiling point elevation
- ΔTb = m x Kb x i
- m = molality, Kb = boiling point constant (°C/m),
- i = van't hoff factor
- B.p. sol higher than B.p. pure solvent
- Π = MRTi
- M = molarity, R = .0821 atm L / mol K, T = temp in K, i = van't hoff factor
- amount of pressure needed to prevent osmotic flow
van't hoff factor
- amount of dissociation that occurs in solution
Types of bonding, what type of element they're between, and how e- react
- ionic (metals to nonmetals) - e- are transferred
- covalent (nonmetals to nonmetals) - e- are shared
- metallic (metal to metal) - e- are pooled
Bond type by electronegativitiy
- 0.0 = pure covalent
- 0.1 - 0.4 = nonpolar covalent
- 0.5 - 1.9 = polar covalent
- 2.0 - 4.0 = ionic
Octet rule exceptions
- H, He have only 2 e-
- Group IIIA elements may have 6 e- only
- Elements in period 3+ may have 8, 10, 12, or 14 e-
The only 3 free radical compounds (exceptions to lone pair rule)
NO, NO2, and ClO2
How do you check a Lewis Dot Diagram?
- Correct # of e-?
- Octet rule?
- Σ Formal Charges = charge of molecule?
Trends in bond length
- More e- shared by atoms = shorter covalent bond
- Bond length decreases from left to right across period
- Bond length increases down the column
Trends in bond energy (energy needed to break a bond)
- More e- shared by atoms = stronger covalent bond
- Shorter covalent bond = stronger covalent bond
Evaluating resonance structures
- Better structures have fewer formal charges
- Better structures have smaller formal charges
- Better structures have negative formal charges on more electronegative atoms
Possible shapes of molecules with VSEPR formula and bond angle
- AX2 - linear - 180˚
- AX3 - trigonal planar - 120˚
- AX2E - v shaped/bent
- AX4 - tetrahedral - 109.5˚
- AX3E - trigonal pyramidal
- AX2E2 - v shaped/bent
- AX5 - trigonal bipyramidal - 120˚ (equatorial) and 90˚ (axial to equatorial)
- AX4E - irregular tetrahedral / seesaw
- AX3E2 - T shaped
- AX2E3 - linear
- AX6 - octahedral - 90˚
- AX5E - square pyramidal
- AX4E2 - square planar
How do lone pairs affect bond angle?
Lone pair "take up more space" and decrease the bond angle between atoms
Which shapes result in non-polar molecules (through vector cancellation) and which shapes result in polar molecules (uncancelled vectors)?
- Nonpolar: linear, trigonal planar, tetrahedral, tigonal bipyramidal, octahedral, square planar
- Polar: bent, trigonal pyramidal, seesaw, t-shaped, square pyramidal
How does Valence bond theory explain bonding? List the hybrids, and their corelation to Lewis dot.
- VBR states that a bond is the overlap of atomic (or hybrid) orbitals.
- Hybrids are created based on the lewis dot structure, based on how many e- densitites the atom has.
- 2 (sp), 3 (sp2), 4 (sp3), 5 (sp3d), 6 (sp3d2)
How do you know how MANY hybrid orbitals to use?
- The number of atomic orbitals combined = the number of hybrids formed
- eg combining a 2s with a 2p gives 2 sp orbitals
Describe the different types of bonds using greek letters, and how each overlaps in depth.
- 1 single bond = 1 δ bond
- 1 double bond = 1 δ bond and 1 π bond
- 1 triple bond = 1 δ bond and 2 π bonds
- δ bonds overlap once, along the axis of the bond using hybrid orbitals
- π bonds overlap twice, perpendicular to axis using unhybridized p orbitals
Explain the steps in proving a hybridization
- Draw the lewis dot structure
- Get the electron configuration for the element
- Establish hybridization based on lewis dot
- Draw energy levels using electron configuration
- Create hybrids and fill in the electrons, make sure it matches (remember p orbitals are unhybridized in π bonds
How does Molecular orbit theory explain bonding?
Electrons belong to whole molecule, orbitals belong to whole molecule (delocalization)
Differences between VBT, MO, and Lewis
- VBT predicts many properties better than Lewis (bonding schemes, bond length, bond strengths, bond rigidity)
- VB presumes electrons are localized, and does not account for delocalization
- VB cannot predict perfectly (magnetic behavior)
- MO can predict bond order, energies, magnetic properties
- Both are used, but have strengths and weaknesses
What forms a bonding molecular orbital? What are the symbols?
- When the two wave functions combine constructively the resulting molecular orbital has less energy than the original atomic orbital
- δ and π are bonding orbitals (most electon density between nuclei)
What forms a antibonding molecular orbital? What are the symbols?
- When the two wave functions combine deconstructively the resulting molecular orbital has more energy than the original atomic orbitals
- δ* and π* are antibonding orbitals (most electon density outside nuclei)
- nodes (spaces without electrons) between nuclei
What is bond order?
- (Bonding electrons - antibonding electrons) / 2
- Only use valence electrons
- higher bond order = stronger/shorter bonds
- fractions possible
MO paramagnetic vs diamagnetic
- paramagnetic (attracted to magnets) if MO diagram has unpared electrons
- diamagnetic (not attracted to magnets) if MO diagram has all electrons paired
LUMO, HOMO, and what they are used for.
- Lowest Unpaired Molecular Orbit
- Highest Occupied Molecular Orbit
- Difference is used to determine wavelength absorpotion by molecule
What is lattice energy (ΔHlattice)? Formulaic definition? What formula/factors affect lattice energy?
- Energy released when 1 mol solid crystal forms from ions in gas state
- ΔHlattice = cation(g) + anion(g) -> 1 mol molecule(s)
- Always exothermic
- Depends on size/charge of ions [direct] and distance between ions [inverse]
- E = C x q1q2/r
E, W, q, C, Cs, ΔH,
- E = Energy - anything that has the capacity to do work (Quantity that an object can posess)
- W = Work - a force acting over a distance (way an onject can exchange E w/ other objects [in and out])
- q = Heat - flow of energy caused by a difference in temperature (way an onject can exchange E w/ other objects [in and out])
- C = Heat capacity - amount of energy required to change an objects temperature by 1 degree C
- Cs = Specific heat - amount of energy required to raise the temperature of 1g substance by 1 °C
- ΔH = total energy of a system (internal E + work) / determines endo/exothermic [ΔH = q (@ constant P)]
Bomb calorimeter details vs Coffee cup calorimeter
- Bomb - Constant volume = -CcalorimeterxΔT
- Coffee - Constant pressure = -Cs x Masss x ΔTs
Standard Conditions (thermodynamics) + symbol
- symbol = °
- gas = 1 atm pressure
- liquid/solid = 1 atm pressure, 25°C
- solution = 1M concentration
Standard Enthalpy of formation (symbol + meaning)?
- ΔHf° - enthalpy change for the reaction forming exactly one mole of a pure compound from its constituent elements at standard conditions
- ΔHf° of elements is always - KJ/mol
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