AP Chem Unit 1

proton

symbol: p⁺ location: nucleus charge: +1 mass: 1amu

neutron

symbol: n⁰ location: nucleus charge: 0 mass: 1amu

electron

symbol: e⁻ location: energy levels (shells) around nucleus charge: -1 mass: 1/1840amu

atomic mass

mass of an atom, measured in atomic mass units (AMU) official definition: 1/12 of a carbon-12 atom

atomic mass unit

measurement used for atomic mass

moles

used to measure atoms, because they are very small and can't be counted

top left number in a nucleotide symbol:

the mass number (protons + neutrons)

bottom left number in a nucleotide symbol:

the atomic number (protons)

mass number

protons + neutrons

top right number in a nucleotide symbol:

charge of element protons-electrons

1 mole=

6.022 x 10²³ particles/formula units

particles

atoms, molecules, or ions

formula units

used for ionic bonds

molar mass

average mass of one mole of a substance in grams (g/mol) for one mole, there are this many grams

average atomic mass

the weighted average of the naturally occurring isotopes for a given element measured in AMU

average atomic mass formula

AAM= (m₁ * %₁) + (m₂ * %₂) + ... (mₙ * %ₙ) remember to change all percentages to decimals!

mass spectrometry

• scientific method to determine the mass of atoms-relative abundance/AAM of samples

• gives the mass-to-charge ratio

• separates isotopes according to mass

• the relative size of the peaks indicates the relative number of particles

• the number of peaks=number of isotopes

pure substances

elements and compounds (molecules) are chemically bound together and need a chemical reaction to separate

mixtures

A combination of two or more substances that are not chemically combined, can physically separate

law of definite proportions

• elements and compounds can only combine in simple, whole number ratios

• if the ratio is different, then the sample is no longer pure and is a mixture instead

2 experiments to determine purity

1. reactions + stoichiometry

2. elemental analysis + empirical formula

elemental analysis

• one of the experiments to help determine purity

• the experimental measurement of the percent composition of elements in a compound

empirical formula

chemical formula showing the smallest whole-number ratio of atoms in a compound

how to do empirical formula

1. assume your sample is 100 grams, and change the percentages to grams

2. convert the grams to moles through dimensional analysis

3. divide all the molar amounts by the last number of moles

• should be close to a whole number--if not, multiply

4. the numbers become the subscripts in the empirical formula

molecular formula

the true, unreduced formula for the atoms in a compound

how to do molecular formula

1. calculate the mass of the empirical formula

2. divide the compound's mass by the mass of the empirical formula (big over small)

3. multiply the subscripts by the number calculated in step 2

alkali metals (4)

• group 1 on periodic table

• most reactive metal family

• react violently with water

• often bind with halogens

alkaline earth metals (2)

• group 2

• hydroxides of these provide basic solutions in water

chalcogen family (2)

• group 16

• found in metal ores

halogen family (4)

• group 17

• known as salt formers

• used in modern lighting

• often bind with alkali metals

noble gas family (3)

• group 18

• known for their lack of reactivity

• once thought to never react

atomic radius trend (4)

• how large the atom is

• increases down and to the left

• down: because of increasing energy level--the more energy shells, the further electrons are from the nucleus and the larger the atom

• across: because the effective nuclear charge increases to the left with less protons, causing it to have less coulombic attraction which doesn't pull electrons in as close

coulombic attraction

The force of attraction between positive and negative charges

ionization energy trend (5)

• the energy it takes to remove an electron from an atom in the gas phase

• only first ionization energy

• increases up and to the right (opposite of atomic radius)

• up: because the smaller the atom is with less energy shells, the smaller the atomic radius is and the closer together the electrons are, making it harder to remove from the nucleus

• right: because the more protons there are, the more coulombic attraction there is which makes it harder to remove an electron

it always takes ___ energy to move more electrons

more

when is there a big change between ionization energies?

when it switches to removing core electrons

notable ionization energy trend exceptions (2)

1. between groups 2 and 13

2. between groups 15 and 16

groups 2 and 13 ionization energy trend exception (2)

• happens because there is a difference in s and p orbitals

• the s orbital has more ionization energy

groups 15 and 16 ionization energy trend exception (2)

• happens because there is a difference in paired and unpaired electrons

• it take less energy to remove a paired electron than unpaired

cations (3)

• positively charged ions (cats are positive)

• lost electrons

• smaller than their atom because: the remaining electrons experience more attraction from the nucleus, making the radius smaller, and if you lose an electron, you have less electron-electron repulsion

anions (3)

• negatively charged ions (onions are negative)

• gained electrons

• larger than their atom because there is more electron-electron repulsion

isoelectric

• things with the same number of electrons

• focus on the number of protons!

orbital notation/Aufbau diagrams

visual method that shows the arrangement of electrons in an atom

how to do orbital notation/Aufbau diagrams

1. write down electron configuration if needed

2. draw blanks for each orbital, with 2 electrons going in each blank (1 for s, 3 for p, 5 for d)

3. draw arrows, with up arrows in each orbital going first and down arrows second

Pauli exclusion principle

No 2 electrons in an atom can have the same set of four quantum numbers

• no atomic orbital can contain more than 2 electrons. - To occupy the same orbital, they must be of opposite spin

Hund's Rule

• the most stable arrangement of electrons is that with the maximum number of unpaired electrons because it minimizes electron-electron repulsions.

• all single electrons have parallel spins to reduce electron-electron repulsions.

• spread out than fill up

s level orbitals

1

p level orbitals

3

d level orbitals

5

f level orbitals

7

s level # of electrons in each orbital

2

p level # of electrons in each orbital

6

d level # of electrons in each orbital

10

f level # of electrons in each orbital

14

center of the atom is _____ charged

positively

electrons in energy shells are ____ charged

negatively

protons and electrons are ____ to each other

attracted

Coulomb's law

• states the relationship between charge of particles and the distance between them

• directly related to the charges of the particles (q)

• inversely related to the distance between the particles (r)

inner electrons have a _____ binding energy than outer electrons because:

greater, because of coulombic attraction

binding energy

amount of energy it takes an electron to leave

photoelectron spectroscopy (5)

• provides data about ionization energy and its applications

• gives electron energy data

• amount of energy tells you about the electron's location--higher energy=closer to nucleus

• relative size of peaks indicates the relative number of electrons

• consistent with electron configuration

electronegativity trend (3)

• ability of an atom in a molecule to attract electrons to itself

• increases up and to the right, no noble gases (same as ionization energy)

• because: shielding effect; also smaller atoms more easily feel charge of nucleus

shielding effect

if a molecule is small, there are less energy shells in the way, so more electrons can be attracted to it--explains electronegativity trend

electron affinity (4)

• amount of energy given off when an electron is added to an atom

• opposite of ionization energy

electron affinity trend

increases to the right because those atoms want another electron a lot (more negative), give off more energy

elements in the same ____ react the same way with other compounds

group

elements in the same group react the same way with other compounds because (3)

• they have the same number of valence electrons

• they have the same ending to their electron configurations

• they have the same oxidation number

valence electrons

electrons in the outermost energy levels of an atom

core electrons

electrons not in the outermost energy level of an atom

oxidation number

• most common ion forming for a given element

• based on the number of valence electrons

• goal is to get a full valence shell (8)

nonmetals _____ ____ electron shells, metals _____ _____ electron shells

fill up, remove outermost