MCAT Chemistry
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- Absorbtion Spectrum
- A dark line spectrum formed when white light is passed through a vaporized element and a few specific wavelengths are absorbed
- Bohr Model of the H Atom
-
1) e- are present only in specific energy states
2) quantum energy is absorbed or emitted to change energy levels
3)Quantum- smallest ammount of energy that can be gained or lost - Ground State
- e- is a t it's lowest energy levels as close to nucleus as possible
- Excited State
- e- absorbs energy + moves to higher energy level above ground state
- 4 Quantum #'s and Symbols
-
n=principal energy level
l=sublevel
m=orbital
s=spin - Sublevel e- cpacity
-
s=2e-
p=6e-
d=10e-
f=14e- - Valence
- # of e- in the atom's highest # d shell
- Electronegativity Difference
-
# found by taking th edifference between the e-negativities of 2 atoms. Value determines bond type.
Values differ by 1.7 or more... ionic - Nonpolar Covalent Bond
- When the e-neg. diff. is very small(less than .5). 2 bonded atoms share velence e- resulting molec has no electrostatic charge.
- Polar Covalent Bond
- e-neg. diff. is btwn. .5-1.7 the bonding e- stay closer to more e-neg. atom... shared unequally.
- Coordinate Covalent Bond
- when both e- in a covalent bond are supplied by one atom
- Metallic Bonds
- sea of e- surrounding positive metal ions
- Hydrogen Bonding
- when H bonds to O,N,F
- Octet Rule
- atoms tend to gain or lose outer shell e- in order to acheive a noble gas config. of 8 e-
- Resonance Structures
- more than 1 possible bonding structure
- Hybrid Orbitals
-
2 or more orbitals mix to form identical hybrid orbitals.
triple bond sp
double bond sp2
single bond sp3 - Properties of ionc substances
-
non-conducting
high mp
brittle
low volatility - properties of molecular substances
-
non-conducting
volatile
many gases
low mp/bp
soft waxy solids - Enthalpy Difference
- difference in heat content btwn the products and reactants
- Exothermic rxn
-
∆H is negative
Enthalpy is decreased - Endothermic rxn
-
∆H is positive
Enthalpy is increased - Hess's Law
- ∆H for a rxn is the same regardless of the path travelled from reactants to products
- Specific Heat
- Ammount heat required to raise 1 g of a subst. 1ËšC
- Equation for energy change when a fixed mass of a subst. changes temp.
- Q=mC∆T
- Charle's Law
- V1/T1=V2/T2
- Boyle's Law
- P1V1=P2V2
- Combined Gas Law
- P1V1/T1=P2V2/T2
- Ideal Gas Law
-
PV=nRT
R=.0802 L-Atm/mol-K - Avogadro's Law
- Under same conditions of temp. and pressure; equal volumes of gases contain equal numbers of moles
- Vol of one mol of any gas at STP
- 22.4 L
- Heat of Fusion
- solid---->liquid
- Heat of Vaporization
- liquid--->gas
- Vapor Pressure
- pressure the gas phase exerts on its liquid phase in a closed container.
- Molarity
-
# of moles solute/ liter of solution
M=n/L - 3 factors that effect rate of sollubility
- pulverizing, stirring, heating
- Molality
-
moles solute/ Kg solvent
m=n/Kg - Gram equivellent weight
- ammount of subst. which reacts w/or displaces 1 mole of H+ ions
- Normality
- # of gram equivelent weights in a liter of solution
- 5 factors that control rxn rate
-
nature of reactants
surface area
concentration
temp.
catalyst - Activation Energy
- Energy necessary for a rxn to begin. Obtained from the kinetic energy released durign a collsion.
- Law of Mass Action
- Rate of chemical rxn is proportional to the product of the concentrations of the reactants
- Specific rate constant
- symbol is "K" in a rate eq. A constant specific to temp. and rxn which is part of every rate eq.
- 2 driving forces of rxns
-
Increased entropy- (disorder)
decreased enthalpy-(heat) - Second law of thermodynamics
- Entropy of univ. increases for any spontaneous process
- Free energy change ∆G
-
property which reflects a systems capacity to do useful work
∆G=∆H-T∆S
∆G negative=spontaneous - Solubility product constant
-
an equil. exists in a saturated soln. btwn. dissolved and undissolved solute "Ksp" is the equil constant for this rxn.
KspAgCl= [Ag+][Cl-] - Arhenius Theory
-
an acid yields protons in soln. (H+)
a base yields OH- - Bronstead Theory
-
an acid is a proton donor
a base is a proton acceptor - Lewis theory
-
ana acid is an e- acceptor
a base is an e- pair donor - Equation for finding vol or molarity when given vol or molarity
- MaxVa=MbxVb
- Anode
- A positively charged electrode which attracts anions where OXIDATION takes place
- Cathode
- A negatively charged electrode which attracts cations where REDUCTION occurs
- Electrode Potential
- a measure in volts of the tendencyof atoms to gain or lose e-.
- Spontaneousredox rxn
- add the electrode potenetials of the 2 half rxns. If the result is positive, the rxn is spontaneous; if negative the rxn is not spontaneous
- Ether
- R-O-R'
- Amine
- R-NH2
- Ester
- R-O-C=O-R
- Amino Acid
- H2N-CRH-COOH
- Alpha Particle
-
Helium nucleus
ejection reduces atomic # by 2 amu and atomic weight by 4 amu. - Beta Particle
-
e- ejected from a nucleus. Neutron decays to proton.
Increases atomic # by 1
high velocity
low energy - Gamma (positron) Radiation
-
doesn't change mass or charge
high energy
travels at speed of light - Transmutation
-
Conversion of an element to a new element due to a change in # of protons
alpha or beta decay - Fission
-
breakdown of heavy nuclei into lighter nuclei
nuclear power - Fussion
-
joining of lighter nuclei to form heavier nuclei.
Sun's Power -
Conversion from
celcius-->farenheit - ËšF=(1.8xËšC)+32
-
Conversion from
celius--->kelvin - K=ËšC+273
- Energy
- ability to do work; it is released or absorbed during chem. rxn's in the form of heat, light, electricity
- Matter
- A susbstance that occupies space and has mass
- Density
- D=(mass)(volume)
- Element
- substance composed of identical atoms
- Compound
-
subst. composed of 2 or more elements chemically combined
NaCl. NH3, H2O - Mixture
- A combination of subst. held together by physical means
- Dalton's Atomic Theory
-
1) an element is composed of identical atoms
2)atoms of different elements have diff. properties
3)compounds are atoms of 2 or more elements chem. combined - Law of Conservation of Mass
- During a chem. reaction matter is neither created or destroyed
- Law of Constant Composition
- Cmpnd always contains the same elements combined in the same in the same portions by mass
- Law of Multiple Proportions
- Same elements may combine to form more than one compound. The ratios are in small whole #'s
- Atomic Mass Unit
- the mass of a proton or neutron is equal to 1 amu
- Atomic #
- # of protons in the nucleus of an atom of an element
- Mass #
- the sum of protons+neutrons in the nucleus of an atom
- Isotope
- atoms which contain the same # of protons but diff. #'s of neutrons
- Molecule
- A group of 2 or more atoms held together by chemical bonds
- Diatomic Elements
- H2,O2,F2,Br2,I2,N2,Cl2
- formal charge
-
charge=
Valence e - 1/2 Nbondinge-Nnonbondinge - percent yield
- actual/theoretical
- limiting reactants
-
1)determine moles needed
2)look at eq. determine limiting reagent - isothermal process
- temp remains constant
- isobaric process
- pressure remains constant
- adiabatic
- no heat exchange
- soluble aqueous soln
-
salts of alkali metals
salts of ammonium
chlorides
bromides
iodides
sulfate ion - insoluble aqueous soln
-
metal oxides
hydroxides
carbonates
phosphates
sulfites - chiral molecules
-
non-superimposable images
handedness - stereoisomers
- same atomic connections but arrange diff. in space
- geometric isomers
- differ in arrangement of atoms around double bond
- determining absolute configuration at a single chiral center
-
1)assign priority by atomic number
2)orient the molecule with the lowest priority substituent at the back
3)lowest priority to highest priority
R=clockwise
S=countercockwise - meso compounds
- contain chiral centers but are not optically active due to an internal plane of symmetry
- specific rotation(alpha)
- observed rotation/concentration(g/ml)Xlength(dm)
- diastereomers
- for any molec with n chiral centers there are 2 to the n sterioisomers
- conformational isomers
- compuonds that differ only by rotation about one or more single bonds
- energy scale of diff conformations
- highest energy=totally eclipsed, eclipsed, gauche, anti
- good leaving groups
- weak bases, halides
- SN1
-
2 steps
dissociation of a molecule into a carbocation and a good leaving group
combination of carbocation with a good nucleophile
slow step is rate determining step
favored in polar protic solvents
racemic products
favored with use of bulky nucleophile
rate=k[RX] - SN2
-
single step rxn
nucleophile performs backside attack and replaces leaving group
favored in polar aprotic solvents
rate=K[Nu][RX]
optically active inverted products - Alkyne reduced to cis alkene
- H2, Pd/BaSO4, quinoline
- Alkyne reduced to trans alkene
- Na, NH3
- activating, ortho/para directing(e- donating)
- NH2, NR2, NHCOR, OR, OCOR, R
- deactivating ortho/para directing (weak e- withdrawing)
- F, Cl, Br, I
- deactivating meta directing (e- withdrawing)
- NO2, SO3H, carbonyl cmpnds, COOH, COOR, COR, CHO
- primary alcohols oxidize to
- aldehydes--->carboxylic acids
- secondary alcohols oxidize to
- ketones
- ways to stabalize the negative charge and thus increase acidity are
-
1)e- withdrawing groups(halides)
2)groups that allow more resonance stabilization (benzyl or allyl substituents) - order fo reactivityof carboxylic acid derivatives
- acyl halides, anhydrides, esters, amides
-
proteins
primary structure -
describes the amino acid sequence and covalent bonds
cystine -
proteins
secondary structure -
describes hydrogen bonding
alpha helix and beta pleated sheets
keratin in hair -
proteins
tertiary structure -
3 dimensional shape of the protein
myglobin
collagen -
proteins
quaternary structure -
arrangement of polypeptide sub units
hemoglobin