Foundations of Chemistry — 60 Terms Defined

Accuracy Foundations of Chemistry Dimensionless The closeness of a measured value to the true or accepted value of the quantity being measured. % error = |measured − true| / true × 100

Allotropy Foundations of Chemistry Dimensionless The existence of an element in two or more distinct structural forms within the same physical state.

Anhydrous Foundations of Chemistry Dimensionless Describing a substance from which all water, including water of crystallisation, has been removed.

Anion Foundations of Chemistry C (charge) A negatively charged ion produced when an atom or molecule gains one or more electrons. X + n e⁻ → Xⁿ⁻

Atom Foundations of Chemistry Dimensionless The smallest particle of an element that retains the chemical identity of that element.

Atomic Mass Unit Foundations of Chemistry u (Da) A mass unit defined as exactly one twelfth the mass of a free, unbound carbon-12 atom in its ground state. 1 u = 1.66053907 × 10⁻²⁷ kg

Atomicity Foundations of Chemistry Dimensionless The number of atoms present in one molecule of an element.

Avogadro's Number Foundations of Chemistry mol⁻¹ The number of elementary entities in one mole of substance, fixed by definition at 6.02214076 × 10²³ mol⁻¹. N = n × N_A

Cation Foundations of Chemistry C (charge) A positively charged ion produced when an atom or molecule loses one or more electrons. M → Mⁿ⁺ + n e⁻

Centrifugation Foundations of Chemistry g (RCF) A separation technique that uses rapid rotation to generate an effective gravitational field, forcing denser components to the bottom of a tube. RCF = 1.118 × 10⁻⁵ × r × N²

Chemical Change Foundations of Chemistry Dimensionless A change in which the atoms of one or more substances are rearranged into new substances with different properties.

Chemical Formula Foundations of Chemistry Dimensionless A symbolic notation that states which elements a substance contains and in what proportions, using element symbols and subscripts.

Chemical Property Foundations of Chemistry Various A characteristic that describes how a substance transforms into a different substance, observable only during a chemical reaction.

Chemical Symbol Foundations of Chemistry Dimensionless The one-, two- or three-letter abbreviation used internationally to represent an element.

Compound Foundations of Chemistry Dimensionless A pure substance formed when two or more different elements combine chemically in a fixed, whole-number mass ratio.

Crystallisation Foundations of Chemistry Dimensionless A purification technique in which a solid is separated from solution as an ordered crystalline lattice.

Dalton's Atomic Theory Foundations of Chemistry Dimensionless The 1808 model proposing that elements consist of indivisible atoms that are identical within an element and combine in fixed whole-number ratios.

Decantation Foundations of Chemistry Dimensionless The separation of a liquid from a settled solid or a denser immiscible liquid by carefully pouring off the upper layer.

Deliquescence Foundations of Chemistry Dimensionless The property of a solid that absorbs enough water vapour from the air to dissolve completely in the water it takes up.

Density Foundations of Chemistry g/cm³ The mass of a substance contained in a unit volume, a characteristic intensive property of each material. ρ = m / V

Dimensional Analysis Foundations of Chemistry Various A calculation method that tracks and cancels units through a chain of conversion factors to reach the required quantity. given quantity × (desired unit / given unit) = answer

Distillation Foundations of Chemistry Dimensionless A separation technique that exploits differences in volatility by vaporising a liquid and condensing the vapour in a separate vessel.

Element Foundations of Chemistry Dimensionless A pure substance composed entirely of atoms that share the same atomic number and therefore cannot be split into simpler substances by chemical means.

Empirical Formula Foundations of Chemistry Dimensionless The chemical formula giving the simplest whole-number ratio of atoms of each element in a compound. ratio = (mass % ÷ A_r), normalised