OCR (B) Chemistry A-level - Elements of Life: Formulae, Equations and Amount of Substance

Key definitions and concepts from OCR (B) Chemistry A-level: Elements of Life, focusing on formulae, equations, atomic structure, and amount of substance calculations.

Ammonium ion

An inorganic ion with the formula $NH_4^+$.

Amount of substance

The quantity of a chemical species, measured in moles. Used as a way of counting atoms. It can be calculated using: $\text{Number of moles} = \frac{\text{Mass}}{M_r}$, $\text{Number of moles} = \frac{\text{Pressure} \times \text{Volume}}{\text{Gas constant, } R \times \text{Temperature}}$, or $\text{Number of moles} = \text{Concentration} \times \text{Volume}$.

Atomic number

The number of protons in the nucleus of an atom.

Atomic orbital

A region of space around the nucleus that can hold up to 2 electrons with opposite spins. There is 1 orbital in the s subshell, 3 orbitals in the p subshell, and 5 orbitals in the d subshell. Orbitals are filled in order of increasing energy, with orbitals of the same energy occupied singly before pairing.

Avogadro constant ($N_A$)

The number of particles per mole of a substance ($6.02 \times 10^{23}\,mol^{-1}$).

Carbonate

An ion with the formula $CO_3^{2-}$.

Composition by mass

The relative mass of each element in a compound.

Concentration

The amount of substance per unit volume. Units are given in $g\,dm^{-3}$ or $mol\,dm^{-3}$.

Electron

A negatively charged subatomic particle that orbits the nucleus at various energy levels. The relative mass of an electron is $\frac{1}{1840}$.

Electronic configuration

The arrangement of electrons into orbitals and energy levels around the nucleus of an atom/ion (e.g., Ca: $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2$).

Empirical formula

The simplest whole-number ratio of atoms of each element present in a compound.