AP Chem- Unit 1

mass spectroscopy

mass spectrum is output which allows us to see most common isotope and average atomic mass

percent composition by mass formula

(molar mass of just element)/(molar mass of whole compound) x 100

empirical formula

lowest whole number ratio of atoms of each element in a compound

molecular formula

actual number of atoms of each element in a coumpound

Aufbau principle

fill lowest energy levels first

Hund’s rule

fills open orbitals with same spin first

Pauli exclusion

within an orbital, electrons must have opposite spins

Coloumb’s law

solves for strength of force between atoms; smaller radius = larger force and smaller charges = smaller force

photoelectron spectroscopy

process that allows us to find out electron configurations of elements by removing electrons and analyzing their kinetic energy

atomic radius trends

bigger down groups b/c of more energy levels, smaller across periods b/c more protons

ionic radius trends

anions bigger, cations smaller (more protons = smaller radius)

ionization energy trends

lower down groups b/c larger radius, less force from nucleus; higher across periods b/c smaller radius

ionization energy exceptions

atoms want full or half-full orbitals, lower IE if taking one away achieves this; higher IE if has full/half full orbital

electron affinity

neutral atom’s likelihood of gaining an electron; more negative = better at gaining electrons (nonmetals greater than metals)

electronegativity trend

the ability of an atom to attract electrons when the atom is part of a compound; increases across periods and decreases down groups

elements with similar properties

in the same group

electron repulsion

electrons in close proximity push each other away, the more electrons there are the greater this will be, makes radius larger