AP Chemistry Unit 1

moles to mass equation

number of moles = mass given / molar mass

moles to particles equation

moles x avagadro’s number (6.022 X 10²³)

mass of an atom

mass of protons + mass of neutrons

isotopes

different versions of an element: same number of protons, different number of neutrons

% composition of elements

(mass of element / total mass of compound) x 100

empirical formula

formula with the lowest whole numbers used

1. assume 100g, change % to grams

2. grams of element/element molar mass = moles of element

3. moles of element / smallest mole number in compound = ratio of elements

4. if not within 0.1 of whole # multiply entire formula until you get a whole number

molecular formula

formula in reality

1. calculate the molar mass of empirical (this will be given)

2. molar mass of molecular/molar mass of empirical = ratio

stoichiometry equation

(g given/molar mass given) x (coefficient unknown / coefficient known) x molar mass unknown = g unknown

% mass in a mixture

(mass of substance / total mass of mixture) x 100 = mass % of substance

rules for electron configuration

1. electrons fill the lowest energy level first

2. electrons spread out in sublevels (parallel before they pair up)

3. electrons in the same orbital must spin in opposite directions

atomic radius

distance form nucleus to valence

• decreases across - more protons pulling electrons in

• increases down - more PEL

• smallest He, largest Fr

ionization energy

energy required to remove electrons from an atom

• increases across - more protons pulling

• decreases down - more PEL causing distance

electronegativity

tendency of an atom to attract electrons from other atoms

• increases across - more protons pulling

• decreases down - more PEL causing distance

NOBLE GASES are exception

valence electrons and ionic compounds

elements in the same group have the same number of valence electrons and tend to form ions with the same charge