MCAT General Chemistry (Princeton Review)

Atomic Number (Z)

# of Protons

Mass Number (A)

# of protons + # of neutrons

Charge (c)

Number of protons - # of electrons

Does energy increase or decrease with distance from the nucleus?

Increase

Does distance increase or decrease with distance from the nucleus?

Decrease

Quantum number n

Describes the radial distance of an electron's orbit from the nucleus

Absorption (Absorbing a photon)

-Positive change in energy
-Endothermic
-Jump to a higher energy level

Emission (Emitting a photon)

-Negative change in energy
-Exothermic
-Drop to a lower energy level

Energy of Photon Equation

Ephoton = Ef - Ei

Energy of Photon in Relation to Wavelength and Frequency Equation

E = hf = hc/λ
-h is a constant
-c is the speed of light

Orbital Energies

Increase with complexity of orbital shape (s<p<d<f)

Degenerate

Same energy

Aufbau Principle

Describes how electrons are added to or removed from orbitals of different energy

Hund's Rule

Describes how electrons are added to or removed from orbitals of the same energy

Pauli Principle

Describes the carrying capacity of an orbital

Valence Electrons

In highest energy shell

Where are electrons added to?

From lowest to highest energy orbitals

Where are electrons removed from?

-From highest to lowest energy orbitals
-Exception: 4s valence electrons are removed before 3d non-valence electrons

Paramagnetic

At least one unpaired electron (attracted by magnet)

Diamagnetic

All electrons are paired (repelled by magnet)

Ground State

Lowest energy electron configuration

Electron Configuration Exceptions

-Chromium: [Ar] 4s1 3d5
-Copper: [Ar] 4s1 3d10

Same Group Elements (going down)

Similar reactivity

Have No Fear Of Ice Cold Beer

-H = gas
-N = gas
-F = gas
-O = gas
-I = solid (ice)
-Ch = gas
-Br = liquid (beer)

Effective Nuclear Charge

Nuclear charge experienced by valence electrons

Moving down a group...

-Core electrons are added at the same rate as protons (Zeff is constant)
-Number of valence electrons remains the same (C remains zero)
-Size of the valence shell increased (n increases)
-Fe decreases

Moving left to right across a row...

-Number of core electrons remain constant while protons are added (Zeff increases)
-Valence electrons are added at the same rate as protons (C remains zero)
-Size of the valence shell remains constant (n remains constant)
-Fe increase

Moving from positive to negative charge...

-Number of core electrons and protons remains constant (Zeff remains constant)
-Number of valence electrons increases while the number of protons remains constant (C becomes more negative)
-Size of valence shell remains constant (n remains the same)
-Fe decrease with increasing negative charge

Atomic Radius Trend

-Increases going down a group
-Decreases going left to right

Ionic Radius Trend

-Increases with increasing negative charge

Ionization Energy

-Minimum amount of energy required to remove the outer most electron from an atom in its gaseous state
-Increases with more positive charge

Ionization Energy Trend

- Increases going up a group
-Increases going left to right

Electron Affinity

Energy change when adding an electron to the valence shell of an atom in its gaseous state

Electron Affinity Trend

-Increases going up a group
-Increases going left to right

Electronegativity

Ability of an atom to attract electrons to itself in a covalent bond

Electronegativity Trend

-Increases going up a group
-Increases going left to
right
-F>O>N>Cl>Br>I>S>C~H

Lewis Dot Structures

-Valence electrons (neg. charge = +1 e- and pos. charge = -1 e-)
-Arrange for least electronegative atom in the center
-Positive charges on less electroneg. atoms
-Negative charges on more electroneg. atoms

Geometric Shape Of Bond

-2 groups = sp = linear
-3 groups = sp2 = trigonal planar
-4 groups = sp3 = tetrahedral

Strength of Chemical Bond

-More electrons shared = stronger bond
-Shorter distance between atoms = stronger bond
-Stronger bond = higher bond dissociation energies

Breaking a Bond

Endothermic

Forming a Bond

Exothermic

Covalent Bonds

-High electroneg.
-Nonmetals with nonmetals
-Electrons localized in bond
-Electrons donated from both atoms
-Insulators and rigid

Metallic Bonds

-Low electroneg.
-Metal with metal
-Electrons delocalized in bond
-Electrons donated from all atoms
-Conductors and malleable

Coordinate Covalent Bonds

-Lone pair and electron deficient species
-Electrons localized between atoms
-Electrons donated from nucleophile
-Easily dissociated

IMF Strength

Larger charges = stronger attractive forces

Ionic Bonds

-Particles of opposite charge
-Electrons localized on ions
-Dissociate in aqueous solution as electrolyte
-Insulators and brittle

Dipole-Dipole Forces

-Between polar molecules
-Easily cleaved

London Dispersion Forces

-Between all molecules
-Very weak and easily cleaved

Hydrogen Bonding

-Between very polar molecules (FON)
-Donor: NH, OH, FH
-Acceptor: N-, O-, F-

Relative strength of different types of IMFs

Ionic> H-bond > Dipole > London Dispersion Forces

Enthalpy (H)

Energy stored within chemical bonds or any attractive force

Exothermic

-Higher energy in reactants than products
-Bonds formed (-)
-ΔH < 0

Endothermic

-Higher energy in products than reactants
-Bonds broken (+)
-ΔH > 0

Enthalpy Equation

Σ bonds broken - Σ bonds formed

Hess's Law

-Reversing direction of the reaction changes the sign of ΔH
-Add rxns together to cancel out intermediate species

Entropy (S)

-Potential randomness
-Increase (S) = increase # of particles, increase temp., increase V
-Changing from solid to liquid to gas increases entropy

Gibbs Free Energy (G)

Energy available to do work

Exergonic

-Spontaneous process
-ΔG = negative

Endergonic

-Non-spontaneous process
-ΔG = positive

Gibbs Free Energy Equation

ΔG = ΔH - TΔS

Condensation

Gas to liquid

Vaporization

Liquid to gas (boiling)

Crystallization

Liquid to solid (freezing)

Fusion

Solid to liquid (melting)

Deposition

Gas to solid

Sublimation

Solid to gas

Triple Point (on phase diagram)

The temp and pressure when all 3 phases coexist in equilibrium

Critical Point (on phase diagram)

The temp and pressure when the difference between liquid and gas is no longer distinct

Water (freezing and melting point)

Decrease under increasing pressure

Density relationship with Pressure

Directly proportional

Density relationship with Temperature

Indirectly proportional

Density relationship with IMF

Directly proportional

Heat Equation

q = mcΔT
-m = mass of substance (g)
-ΔT = change in temp. (C)
-c = specific heat (J/gC)
-C = mc = heat capacity (J/C)

Vapor Pressure relationship with Pressure

No effect

Vapor Pressure relationship with Temperature

Directly proportional

Vapor Pressure relationship with IMF

Indirectly proportional

Boiling Point (bp)

-Temp at which condensation/vaporization phase transition occurs
-When Pvap = Patm

BP relationship with Pressure

Directly proportional

BP relationship with IMF

Directly proportional

Melting Point (mp) and Freezing Point (fp)

-Temp at which fusion/crystallization phase transitions occur
-Increased mp = harder to melt
-Increased fp = easier to freeze

MP/FP relationship with Pressure

Directly proportional

MP/FP relationship with IMF

Directly proportional

Solvent on MCAT

Water

Solute

Usually present in smaller quantity

Solvent

Usually present in larger quantity

Strong Electrolyte Solute

Complete dissociation

Weak Electrolyte Solute

Partial dissociation

Non-Electrolyte Solute

No dissociation

Agitation

Endothermic

Dissociation

Endothermic

Solvation

Exothermic

Electrolytes dissolve in water...

Agitation --> dissociation --> solvation

Polar non-electrolytes dissolve in water...

Agitation --> solvation

Nonpolar non-electrolytes do not dissolve in water...

Agitation

Always soluble groups

Group I ions
-H+
-NH4+
-NO3-
-CH3COO-
-ClO4-

Usually insoluble groups

-Ag+
-Pb2+
-Pb4+
-Hg2 2+
-Hg2+
-CO3 2-
-PO4 3-
-S 2-

Solubility (S)

Amount of substance that can dissolve in a specific solvent at a specific temperature

Unsaturated Solution

-Concentration < Solubility
-Additional solute can still dissolve

Saturated Solution

-Concentration = Solubility
-No additional solute will dissolve
-Precipitant will form

Supersaturated Solution

-Concentration > Solubility
-Additional solute causes excess to precipitate
-Precipitant will form