ORELA Chemistry (NT321) key terms

The amount of substance containing 6.022 × 10^23 representative particles, used as the base counting unit for chemical calculations. It links mass in grams to particle number through molar mass.

The mass in grams of one mole of a substance, numerically equal to its formula mass in atomic mass units. It converts between grams and moles in stoichiometric problems.

The value 6.022 × 10^23, giving the number of particles in one mole of any substance. It bridges microscopic particle counts and macroscopic amounts measured in the laboratory.

The simplest whole-number ratio of atoms of each element in a compound. It is found by converting percentage composition or masses to moles and dividing by the smallest mole value.

The actual number of atoms of each element in one molecule of a compound. It is a whole-number multiple of the empirical formula, determined using the compound's molar mass.

The mass percentage of each element in a compound, calculated by dividing the total mass of that element in one mole by the molar mass and multiplying by 100.

The reactant that is completely consumed first and therefore determines the maximum amount of product formed. Excess reactants remain after the reaction stops.

The maximum mass of product predicted by stoichiometry when the limiting reactant is fully consumed. It is compared with actual yield to compute percent yield.

The ratio of actual experimental yield to theoretical yield, multiplied by 100. Values below 100 percent reflect side reactions, incomplete reactions, or product loss during handling.

The quantitative relationship among reactants and products in a balanced chemical equation, using mole ratios from coefficients to convert between substances.

Concentration expressed as moles of solute per liter of solution. It is the most common unit for solution stoichiometry and dilution calculations.

The process of adding solvent to reduce concentration, described by the relationship that initial molarity times initial volume equals final molarity times final volume, because moles of solute stay constant.

The number of protons in an atom's nucleus, which uniquely identifies the element and determines its position on the periodic table.

The sum of protons and neutrons in a nucleus. It distinguishes isotopes of the same element but is not a periodic-table ordering value.

An atom of the same element with a different number of neutrons, so it has the same atomic number but a different mass number. Isotopes share chemical properties but differ in mass.

The weighted average of isotope masses using natural abundances. It produces the non-integer atomic masses listed on the periodic table.

The principle that properties of elements vary periodically with increasing atomic number, explaining repeating trends across periods and down groups.

A measure of atomic size, generally decreasing across a period as nuclear charge grows and increasing down a group as additional electron shells are added.

The energy required to remove an electron from a gaseous atom. It generally increases across a period and decreases down a group as outer electrons are shielded and farther from the nucleus.

The relative tendency of an atom to attract shared electrons in a bond. It increases across a period and decreases down a group, helping predict bond polarity.

A set of four values (principal, angular momentum, magnetic, spin) that specify the energy, shape, orientation, and spin state of an electron in an atom.

The arrangement of electrons among atomic orbitals, written following the Aufbau principle, Pauli exclusion principle, and Hund's rule.

A region of space where an electron is most likely to be found, holding at most two electrons with opposite spins. Orbitals have characteristic shapes labeled s, p, d, and f.

Electrons in the outermost shell that participate in bonding and determine an element's chemical behavior and group placement.

An electrostatic attraction between oppositely charged ions formed by transfer of electrons, typically between a metal and a nonmetal with large electronegativity difference.

A bond formed by sharing electron pairs between atoms, commonly between nonmetals. Shared electrons may be distributed equally or unequally, producing nonpolar or polar bonds.

A covalent bond in which electrons are shared unequally because the bonded atoms differ in electronegativity, producing partial charges and often a molecular dipole.

A diagram showing valence electrons as dots and bonds as lines, used to predict bonding, lone pairs, and molecular geometry through VSEPR theory.

A model predicting molecular shape from electron-pair repulsion around a central atom, counting bonding and lone pairs to determine geometry and approximate bond angles.

The representation of a molecule by two or more equivalent Lewis structures whose combination describes delocalized electrons more accurately than any single structure.

The net dipole of a molecule, determined by both bond polarities and molecular geometry. Symmetric arrangements of polar bonds can cancel and yield a nonpolar molecule.

Attractions between molecules, including London dispersion, dipole-dipole, and hydrogen bonding, which influence boiling point, melting point, vapor pressure, and solubility.

A strong intermolecular attraction between a hydrogen atom bonded to N, O, or F and a lone pair on a nearby electronegative atom, raising boiling points notably.

Physical properties that depend on the number of dissolved solute particles rather than their identity, including vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.

A homogeneous mixture of solute dissolved in solvent at the particle level. Its components cannot be separated by filtration and it has uniform composition throughout.

The maximum amount of solute that dissolves in a given quantity of solvent at a specified temperature, often expressed in grams per 100 grams of solvent.

The condition in which a solution contains the maximum solute it can dissolve at a given temperature, so additional solute remains undissolved.

The rule that a system at equilibrium shifts to partially offset a change in concentration, temperature, or pressure applied to it.

The ratio of product concentrations to reactant concentrations at equilibrium, each raised to its coefficient power. It indicates the extent of reaction at a given temperature.

The minimum energy colliding particles must possess for a reaction to occur. Catalysts lower it by providing an alternative pathway without being consumed.

A substance that increases reaction rate by lowering activation energy while remaining chemically unchanged overall. It does not alter the equilibrium position of a reversible reaction.

An equation expressing reaction rate as a constant times reactant concentrations raised to experimentally determined powers, which are not necessarily the balanced-equation coefficients.

The negative base-10 logarithm of hydrogen ion concentration, indicating acidity on a scale typically from 0 to 14 at room temperature.

A solution that resists pH change when small amounts of acid or base are added, usually made from a weak acid and its conjugate base or a weak base and its conjugate acid.

The loss of electrons by a species, accompanied by an increase in oxidation state. It always occurs together with reduction in a redox reaction.

The gain of electrons by a species, accompanied by a decrease in oxidation state. It occurs simultaneously with oxidation in a redox process.

A formal charge assigned to an atom by applying electron-assignment rules, useful for identifying redox changes and balancing oxidation-reduction equations.

A device converting chemical energy to electrical energy (galvanic) or the reverse (electrolytic), consisting of electrodes in electrolyte solutions connected by a circuit.

The time required for half of a radioactive sample to decay. It is characteristic of each isotope and independent of the starting amount.

The spontaneous emission of particles or radiation from an unstable nucleus, transforming it toward a more stable configuration through alpha, beta, or gamma processes.

The study of heat absorbed or released during chemical reactions, described by enthalpy changes and governed by the laws of thermodynamics.

A thermodynamic quantity representing heat content at constant pressure, with change in enthalpy equal to heat transferred in many reactions.

Relationships among pressure, volume, temperature, and amount of gas, including Boyle's, Charles's, and the ideal gas law, which combine into the ideal gas equation.