AP CHEMISTRY Unit 1: Atomic Structures and Properties

Sig-fig rules

Non zero digits are significant

zeros between non-zero digits are significant

leading zeros are not significant

only trailing zeros with a decimal are significant

Adding/subtracting with sig figs

use fewest number of decimal places

multiplying/dividing with sig figs

fewest number of sig figs

correct way of taking measurements

All given values plus and estimated digit

Isotopes

Same number of protons

Different number of neutrons

Average atomic mass

weighted average of isotopes

(mass x % abundance) +(mass2 x % abundance) +…

Empirical formula

simplest mole ratio of elements within a compound

molecular formula

actual number of atoms within a compound

Grams —> empirical formula

Grams of element —> molar mass —> moles —> calculate mole ratio by dividing by lowest mole —> empirical formula

Compositional analysis

mass % of elements —> assume 100 g sample —> grams of each elements —> use molar mass —> moles —> calculate mole ratio by dividing by lowest mole —> empirical formula

Combustion analysis with oxygen

Mass of CO2 and H20 —> molar mass of CO2 and H20 —> mole of CO2 and H20 —> mole ratio of C and H —> mole of C and H —> grams of C and H —> subtract from total mass —> grams of O —> molar mass of O —> moles of O —> calculate overall mole ratio by dividing by lowest mole ratio —> empirical formula

Finding molecular formula

compound’s mass / mass of empirical formula = factor —> multiply each element in empirical formula by that factor —> molecular formula

Percent composition

mass of element in compound / molar mass of compoud

Aufbau principle

electrons fill lowest energy level before moving on to higher energy levels

Pauli exclusion principle

one orbital can only hold 2 electrons; one spinning up and the other down

Hund’s rule

Every orbital will be singly occupied before being doubly occupied

Ionization energy

energy required to remove an electron and turning it into an ion

Coulomb’s law

Potential energy/ionization energy depends on charge and distance

Force and distance have inverse relationship

Force and charge have direct relationship

Coulombic attraction trends

Decreases down a group and increases across a period

Effective nuclear charge

How much energy/pull is felt by valence electrons

Symbol: Zeff

protons - electrons in 1st orbital

Higher nuclear charge = more attraction towards the nucleus = smaller atom = harder to remove/ionize

Successive ionization energies

Big gap between numbers shows how many valence electrons there are

Photoelectron Spectroscopy

shows energy required to remove electron from subshell

height shows number of electrons in that subshell

Higher binding energy is where the nucleus is

The more protons an element has the higher the binding energy so therefore the graph would shift to the higher side

Atomic radius trend

increases down a group

decreases across a period

ionic radius

Cations are smaller than their neutral ions

Anions are larger than their neutral atoms

Electronegativity

ability to attract electrons

Electronegativity trends

Decreases down a group

increases across a period

Alkali earth metals

group 1

alkaline earth metals

group 2

halogens

group 17