Foundations of Chemistry — 60 Terms Defined

Polyatomic Ion Foundations of Chemistry C (charge) A covalently bonded group of atoms that carries an overall electrical charge and behaves as a single unit in reactions.

Precision Foundations of Chemistry Dimensionless The closeness of repeated measurements of the same quantity to one another, regardless of their accuracy. RSD = (s / x̄) × 100

Pure Substance Foundations of Chemistry Dimensionless Matter with a fixed chemical composition and a definite set of physical properties, comprising either a single element or a single compound.

Purity Foundations of Chemistry Dimensionless The mass fraction of the desired substance in a sample, usually expressed as a percentage of the total mass. purity % = (mass of pure substance / total mass) × 100

Reagent Foundations of Chemistry Dimensionless A substance added to a system to bring about a chemical reaction or to test for the presence of another substance.

Relative Atomic Mass Foundations of Chemistry Dimensionless The weighted average mass of the atoms of an element, expressed relative to one twelfth the mass of a carbon-12 atom. A_r = Σ(isotope abundance × isotope mass)

SI Base Units Foundations of Chemistry Various The seven defined units of the International System from which every other measurement unit is derived.

Significant Figures Foundations of Chemistry Dimensionless The digits in a measured value that carry meaningful precision, comprising all certain digits plus one estimated digit.

Standard Temperature and Pressure Foundations of Chemistry K, kPa A defined reference condition used to report and compare gas measurements, currently 0 °C and 100 kPa under IUPAC. T = 273.15 K, p = 100 kPa

Structural Formula Foundations of Chemistry Dimensionless A representation showing how the atoms in a molecule are connected and, often, how they are arranged in space.

Valency Foundations of Chemistry Dimensionless The combining capacity of an element, equal to the number of electrons an atom gains, loses or shares when forming compounds.

Water of Crystallisation Foundations of Chemistry mol per mol Water molecules chemically bound within the crystal lattice of a hydrated salt in a fixed stoichiometric ratio.