MCAT General Chemistry

atomic number (z)

equal to number of protons

mass number (A)

sum of protons/neutrons in nucleus

isotopes

atoms with same atoms number but different mass number

cation

• loses electrons

anion

• gains electrons

atomic weight

weighted average of isotopes

ground state

state of lowest energy at lowest possible orbitals

excited state

at least one electron has moved to a sub shell of higher than normal energy

line spectrum

each line on an emission spectrum corresponds to a specific electron transition

• Lyman series: energy levels n >= 2 to n = 1

• Balmer series: energy levels n >= 3 to n=2

• Parschen series: energy levels n >= 4 to n= 3

Heisenberg Uncertainty Principle

it is impossible to simultaneously determine, with perfect accuracy, the momentum and the position of an electron

Pauli Exclusion Principle

no two electrons in a given atom can possess the same set of 4 quantum numbers (n, l, ml, ms)

magnetic quantum number

specifies particular orbital within a sub shell the electron is most likely to be found

paramagnetic

materials composed of atoms with unpaired electrons

• magnetic field will cause parallel spins in unpaired electrons and cause attraction

diamagnetic

materials consisting of atoms with only paired electrons

• slightly repelled by magnetic field

periodic law

the chemical and physical properties of the elements are dependent upon their atomic numbers

A elements

• representative elements

• groups IA through VIIIA

• valence electrons in the orbitals of either s or p

B elements

• non-representative elements

• transition elements —> valence electrons in s and d

• lanthanide and actinide series —> s and d sub shells

metals

• decreased effective nuclear charge, electronegativity, ionic radius, ionization energy, electron affinity

• increased atomic radius

• valence electrons are loose, free to move, good conductors of heat and electricity

nonmetals

• increased ionization energy, electron affinity, electronegativity

• poor conductors of heat/electricity

metalloids

• semimetal: share some characteristics with metals and nonmetals

• tend to follow the trend based on which side of the metalloid line they fall on

atomic radius

equal to one half of the distance between the center of two atoms of an element that are briefly in contact

• decreased left —> right

ionization energy

• energy required to remove an electron from a gaseous species

• requires heat —> endothermic process

• first ionization energy: energy necessary to remove the first electron

• second ionization energy: energy necessary to remove the second electron

electron affinity

energy dissipated by gaseous species when it gains an electron

electronegativity

measure of the attractive force that an atom will exert on an electron in a chemical bond

alkali metals (group 1 or IA)

• decreased ionization energy, electron affinity, electronegativity

• low Zeff values, largest atomic radii

alkaline earth metals (group 2 or IIA)

• smaller atomic radii

• share characteristics with alkali metals

noble gases (group VIIIA/18)

• inert gases because they have minimal chemical reactivity due to filled valence shell

• decreased boiling points, exist as gas in RT

• increased ionization energy

transition metals (groups IB-VIIIB/3-12)

• decreased electron affinity, ionization energy, electronegativity

• increased melting and boiling point

• can have different oxidation states

chalcogens (group VIA/16)

• nonmetals and metaloids

• crucial for normal biological functions

• can be toxic at high concentrations

halogens (group VIIA/17)

• highly reactive nonmetals

• especially reactive toward alkali and alkaline earth

• found as ions (halides)

ionic bonding

• one of more electron form an atom with a low ionization energy (metal) are transferred to an atom with a high electron affinity (nonmetal)

• electrostatic attraction creates lattice structure

• occur between elements with large differences in EN (>1.7)

• high melting and boiling point

covalent bonding

electron pair shared between atoms, typically nonmetals, that have relatively similar values of EN

• non polar: electron pair shared equally

• polar: electron pair shared unequally

• coordinate: both shared electrons are contributed by only one of the two atoms

• lower melting and boiling points

bond length

• average distance between the two nuclei of atoms in a bond

• atoms pulled closer to each other, decrease in bond length

• 3 < 2 < 1

bond energy

• energy required to break a bond by separating its compounds into their isolated, gaseous atomic states

• increase pairs, increase energy to break bonds

• 3 > 2 > 1

polarity

• occurs when 2 atoms have a relative difference in EN

  • partial negative: more EN element acquiring a greater portion of electron density

  • partial positive: less EN element acquiring a smaller portion of electron density

resonance structures

Lewis structures that demonstrate the same arrangement of atoms but differ in the specific placement of electrons

• Lewis structure with no or small formal charge preferred over Lewis structure with large formal charges

• Lewis structure with less separation between opposite charges is preferred over Lewis structure with a large separation of opposite charges

• Lewis structure in which negative formal charges are placed on more EN atoms is more stable than one in which the negative formal charges are placed on less EN atoms

valence shell electron pair repulsion theory (VSEPR)

uses Lewis dot structures to predict molecular geometry of covalently bonded molecules

electronic geometry

spatial arrangement of all pairs of electrons around the central atom, including both the bonding and the lone pairs

molecular geometry

spatial arrangement of only the bonding pairs of electrons

coordination number

number of atoms that surround and are bonding to a central atom

sigma bond

allows for free rotation about their aces because the electron density of the bonding orbital is a single linear accumulation between the atomic nuclei

pi bond

do not allow for free rotation because the electron densities of the orbitals are parallel and cannot be twisted in such a way that allows continuous overlapping of the clouds of electron densities

London dispersion forces

• type of van Der Waals forces

• result of induced dipoles that change and shift moment to moment

• adhesion

dipole-dipole interactions

• present in solid and liquid phases but become negligible in the gas phase because of the distance between gas particles

hydrogen bonds

• unusually strong form of dipole-dipole interaction

• may be intra or intermolecular

• positively charged hydrogen atom interacts with partial negative of fluorine, oxygen, or nitrogen

• high boiling point

molecule

combination of two or more atoms held together by covalent bonds

formula weight

add up atomic weights of the constituent ions (amu)

mol

quantity of any substance equal to the number of particles that are found in 12g of C-12

molar mass

mass of one mole of a compound (g/mol)

equivalents

how many moles of the thing are we interested in will one mole of a given compound produce?

gram equivalent weight

amount of a compound, measured in grams, that produces one equivalent of the particle of interest

normality

measure of concentration (equivalents/L)

empirical formula

• gives the simplest whole number ratio of the elements in the compound

• C2H6O

molecular formula

• gives the exact number of atoms of each element in the compound and is a multiple of the empirical formula

• C6H12O3

percent composition

percent of a specific compound that is made up of a given element

combination reaction

2 or more reactants forming one product

decomposition reaction

single reactant breaks down into 2 or more products

combustion reaction

involves a fuel and form 2 products of carbon dioxide and water

single displacement reaction

occurs when an atom or ion in a compound is replaced by an atom or ion of another element

double displacement/metathesis reaction

• elements from two different compounds swap places with each other to form new compounds

• occurs when one of the products is removed from the solution as precipitate or gas or combine to form a weak electrolyte that remains undissociated in a solution

neutralization reaction

type of double displacement reaction in which acid reacts with base to produce a salt