AS Chemistry

Relative atomic mass is the weighted average mass of the atoms of an element, compared with one-twelfth of the mass of an atom of carbon-12.

Relative molecular mass is the sum of the relative atomic masses of the atoms in a molecule.

The mole is the amount of substance that contains as many particles (atoms, molecules, ions) as there are atoms in 12 g of carbon-12. This is approximately
6.02
×
1
0
23
6.02×10
23
particles (Avogadro's constant).

Avogadro’s law states that equal volumes of gases, at the same temperature and pressure, contain the same number of molecules.

The empirical formula is the simplest whole-number ratio of the atoms of each element in a compound.

The molecular formula is the actual number of atoms of each element in a molecule of the compound.

Boyle’s law states that the pressure of a fixed amount of gas is inversely proportional to its volume, provided the temperature remains constant.

Charles’s law states that the volume of a fixed amount of gas is directly proportional to its absolute temperature, provided the pressure remains constant.

The ideal gas equation is
P
V
=
n
R
T
PV=nRT, where
P
P is pressure,
V
V is volume,
n
n is the number of moles,
R
R is the gas constant, and
T
T is the absolute temperature.

The first ionization energy is the energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.

Electronegativity is the ability of an atom to attract the bonding electrons in a covalent bond.

A covalent bond is a bond formed by the sharing of a pair of electrons between two atoms.

An ionic bond is a bond formed by the electrostatic attraction between positively charged cations and negatively charged anions.

Metallic bonding is the electrostatic attraction between positively charged metal ions and delocalized electrons.

A polar covalent bond is a bond between two atoms where the bonding electrons are shared unequally, due to a difference in electronegativity.

The octet rule states that atoms tend to form bonds to have eight electrons in their outer shell, similar to the electron configuration of a noble gas.

Enthalpy change is the heat energy change at constant pressure.

An exothermic reaction is a reaction in which energy is released to the surroundings, usually in the form of heat. The enthalpy change (ΔH) is negative.

An endothermic reaction is a reaction in which energy is absorbed from the surroundings. The enthalpy change (ΔH) is positive.

Activation energy is the minimum energy required for a reaction to occur by allowing reactant particles to collide with sufficient energy to break bonds.

Hess's law states that the total enthalpy change for a reaction is the same, regardless of the route taken, as long as the initial and final conditions are the same.

Dynamic equilibrium occurs when the rates of the forward and reverse reactions are equal, and the concentrations of reactants and products remain constant over time.

Le Chatelier's principle states that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will adjust to counteract that change and restore a new equilibrium.

Oxidation is the loss of electrons or an increase in oxidation state by a substance.

Reduction is the gain of electrons or a decrease in oxidation state by a substance.

The oxidation state of oxygen in most compounds is -2.

The oxidation state of hydrogen in most compounds is +1.

A redox reaction is a reaction in which oxidation and reduction occur simultaneously.

The rate of reaction is the change in concentration of a reactant or product per unit time.

A catalyst is a substance that increases the rate of a reaction by providing an alternative reaction pathway with a lower activation energy, without being consumed in the process.

A homologous series is a family of organic compounds that have the same functional group, similar chemical properties, and differ by a CH₂ unit.

A functional group is an atom or group of atoms that defines the structure and reactivity of a particular class of organic compounds.

Isomerism is the existence of two or more compounds with the same molecular formula but different structural or spatial arrangements of atoms.

A structural isomer is a compound with the same molecular formula as another compound but with a different structural arrangement of atoms.

A stereoisomer is a compound that has the same molecular formula and the same structural formula but differs in the arrangement of atoms in space.

Nucleophilic substitution is a reaction in which a nucleophile replaces a leaving group in a molecule.

An elimination reaction is a reaction in which atoms or groups are removed from a molecule, resulting in the formation of a double bond.

Electrophilic addition is a reaction in which an electrophile adds to a double or triple bond in an unsaturated compound.

Esterification is a chemical reaction between a carboxylic acid and an alcohol to form an ester and water, usually catalyzed by an acid.

Hydrolysis is the chemical breakdown of a compound due to reaction with water.