Unit 1: atomic structure and properties Ap Chemistry Mrs. Coleman

avogadro’s number

6.02× 10^23 particles

1 mol in L at STP

22.4

(mass #)(%abundance(in decimal form)) + (mass #)(%abundance)…

atomic mass formula

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

percent comp

Empirical formula step 1

change % to grams then grams to moles

Empirical formula step 2

divide by lowest number of moles for ratio

Empirical formula step 3

if mile ratio not whole number multiply by 2/3

Empirical formula step 4

divide molar mass of compound by molar mass of ef

Empirical formula step 5

multiply ef by ratio in previous step for molecular formula

ionization energy down a group

more distance and more shielding between nucleus and outer electrons which makes it easier to remove an electron

ionization energy across a period

more protons in nucleus= stronger attraction between nucleus and electrons= harder to remove an electron

atomic radius

distance from nucleus to the outermost electron

atomic radius across a period

increasing nuclear charge pulls electrons closer ( decreasing)

atomic radius down a group

new energy levels added making atom larger (increasing)

ionic radius

size of an ion (distance from nucleus of ion to outermost electron)

cations

positive ions r smaller than their atoms bc of less electron repulsion

anions

negative ions r larger than their atoms bc of more electron repulsion

electron affinity

the energy change that occurs when a gaseous atom gains an electron ( mor negative mor enegry released mor attraction between electron and nucleus)

electron affinity across a period

more negative (favorable)

electron affinity down a group

less negative(less favorable)

electronegativuty

the power of an atom to attract electrons to itself

effective nuclear charge ( Zeff)

net positive charge Felt by an electron after accounting for shielding by inner electrons

Zeff

=(actual nuclear charge) - (shielding from inner electrons)

Zeff increases

electrons more tightly held

higher zeff

smaller atomic radius

higher ionization energy

lower Zeff

larger atomic radius and lower ionization energy