AP Chemistry

isotope

element with a different number of neutrons

mass spectrometry

mass of elements

avogadros number

6.022 E23

? L/mol

22.4 L

empirical formula

simplest ratio of the molecules making up a compound

molecular formula

actual formula for a substance

coulombs law

the amount of energy that an electron has depends on its distance from the nucleus of an atom; e=k(q1*q20)/r

ionization energy

amount of energy necessary to remove electrons from an atom (electromagnetic energy exceeds binding energy)

shielding electrons

electrons between a valence electron and the nucleus that decreases the attraction between the nucleus and the valence electron

periodic trend: left to right

periodic trend: atomic radius decreases; protons are added to the nucleus so valence electrons are more strongly attracted

ionization energy increases (protons are added to the nucleus)

periodic trend: down a group

periodic trend: atomic radius increases; shells of electrons are added which shield the more distant shells and valence e- get farther away

ionization energy decreases (shells of e- added, each inner shell shields more and reduces the pull on valence e- so they are easier to remove)

ionic bond

bond between metal and nonmetal; electrons are NOT shared: the cation gives an e- up to the anion

metallic bonding

bond between two metals; sea of electrons that make metals such good conductors; delocalized structure allows for malleability and ductility

interstitial alloy

metal atoms with vastly different radii combine; ex. steel

substitutional alloy

metal atoms with similar radii combine; ex. brass

covalent bonds

bond in which two atoms share electrons; each atom counts the e- as a part of its valence shell

single bonds

one sigma bond, one e- pair; longest bond, least energy

double bonds

one sigma bond, one pi bond; two e- pairs

triple bonds

one sigma bond, two pi bonds; 3 e- pairs; shortest bond, most energy

network covalent bonds

lattice of covalent bonds; network solid (acts similar to one molecule); very hard, high melting/boiling points; poor conductors

the common network solids

SiO2,

doping

the addition of an impurity to an existing lattice

p-doping

create a hole (positively charged) that draws electrons through the substance (add a substance with one LESS valence e-) i.e. si + al

n-doping

add a substance with one MORE valence e- which leaves a free e- to travel freely
i.e. si + p

polarity

exists when a molecule has a clustering of negative charge on one side due to unequal sharing of electrons (e- are pulled to the more electronegative side); creates dipoles in molecules

dipole moment

the measurement of the polarity of a molecule; the unit of measurement is a debye (D)

more polar molecule....

.... larger dipole moment

intermolecular forces (IMFs)

forces that exist between molecules in a covalently bonded substance; not bonds

dipole-dipole forces

the positive end of one polar molecule is attracted to the negative end of another molecule; relatively weak attraction force

hydrogen bonding

strong IMF between two moelcules; F, O, N; have higher melting and boiling points than molecules with other IMFs

london dispersion forces

IMFs that occur between all molecules; occur because of the random motions of electrons on atoms within molecules to create instantaneous polarities; molecules with more e- will have greater _________________ forces

substances with only london dispersion forces usually...

... are gases at room temp, and boil/melt at extremely low temps

melting & boiling points of a covalent substance is almost always _____________ than that of ionic substances

lower

vapor pressure

the pressure exerted by a vapor over a liquid

resonance structures

structures that occur when it is possible to draw two or more valid lewis electron dot diagrams that have the same number of electron pairs for a molecule or ion

formal charge

used to find which structure is most likely to occur; valence - assigned

linear geometry

sp hybridization
0 lone pairs
ex. BeCl2 & CO2

trigonal planar geometry

sp2 hybridization
bond angles 120
0 lone pairs: trigonal planar (three bonds)
1 lone pair: bent (two bonds)

tetrahedral geometry

4 e- pairs, sp3 hybridization
angles 109.5
0 lone pairs: tetrahedral (four bonds) [CH4, NH4+, ClO4-, SO4 2-, PO4 3-]
1 lone pair: trigonal pyramidal (3 bonds) [NH3, PCl3, SO3 2-]
2 lone pairs: bent (2 bonds) [H2O, OF2, NH2-]

trigonal bipyramidal geometry

5 e- pairs, sp4 hybridization
0 lone pairs: trigonal bipyramidal (5 bonds) [PCl5, PF5]
1 lone pair: seesaw (4 bonds) [SF4, IF4+]
2 lone pairs: t-shaped (3 bonds) [ClF3, ICl3]
3 lone pairs: linear (2 bonds) [XeF2, I3-]

octahedral geometry

6 e- pairs, sp5 hybridization
0 lone pairs: octahedral (6 bonds) [SF6]
1 lone pair: square pyramidal (5 bonds) [BrF5, IF5]
2 lone pairs: square planar (4 bonds) [XeF4]

maxwell-boltzmann diagrams

shows the range of velocities for molecules of a gas

effusion

the rate at which a gas will escape from a container through microscopic holes in the surface of the container

mole fraction

moles of substance/total moles in solution

dissociation

when ionic substances break up into ions into solution

electrolytes

free ions in solution that conduct electricity

paper chromatography

the separation of a mixture by passing it through a medium in which the components of the solution move at different rates

retention factor

stronger the attraction between the solute and the solvent front is, the larger the Rf value will be

column chromatography

a column is packed with stationary substance, then the solution to be separated (analyte) is injected into the column where it adheres to the stationary phase, then the eluent solution is injected into the column. as the eluent solution passes through the stationary phase the analyte molecules will be attracted to it with varying degrees of strength based on polarity

distillation

the process that separates the substances in a solution based on their boiling points

precipitation reaction

a reaction in which an insoluble substance (salt) forms and separates from the solution

net ionic equation

an equation for a reaction in solution showing only those particles that are directly involved in the chemical change

limiting reactant

the substance that controls the quantity of product that can form in a chemical reaction; moles of each reactant divided by moles used in reaction

gravimetric analysis

a type of quantitative analysis in which the amount of a species in a material is determined by converting the species to a precipitate that can be isolated completely and weighed

when bonds are formed

...energy is released

when bonds are broken

...energy is absorbed

exothermic

products have stronger bonds than the reactants; heat is released, - ΔH

endothermic

reactants have stronger bonds than the products; heat is absorbed, + ΔH

activation energy

the minimum amount of energy required to start a chemical reaction

catalyst

substance that speeds up a reaction by reducing the activation energy required by the reaction; provides an alternate reaction pathway; no effect on equilibrium conditions

oxidation number: H

+1

entropy

ΔS; a measure of the randomness or disorder of the system

enthalpy

ΔH; heat of a system at constant pressure

Gibbs free-energy

ΔG; a measure of whether or not a process will proceed without the input of outside energy
∆G=∆H-T∆S (T in degrees Kelvin)
when ΔG=0, the reaction is at equilibrium

spontaneous

thermodynamically favored; -ΔG

nonspontaneous

thermodynamically unfavored; +ΔG

Arrhenius acids

a substance that ionizes in water and produces hydrogen ions

Arrhenius bases

a substance that ionizes in water and produces hydroxide ions

Brønsted-Lowry acids

a substance that is capable of donating a proton

Brønsted-Lowry bases

a substance that is capable of accepting a proton

pH

-log [H+]

pOH

-log [OH-]

pKa

-log [Ka]

pKb

-log [Kb]

amphoteric

a substance that can act as both an acid and a base; ex. H2O

strong acids

dissociate completely in water; reaction goes to completion and never reaches equilibrium

weak acid

most of the acid molecules remain in solution and very few dissociate

percent dissociation

the ratio of the amount of a substance that is dissociated at equilibrium to the initial concentration of the substance in a solution, multiplied by 100

oxoacids

acids that contain oxygen; the more oxygens, the stronger the acid

polyprotic acids

acids that can donate more than one H+

Kw

1.0x10^-14

henderson hasselbach

pH = pKa + log([A-]/[HA])

buffers

weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH