AQA A-Level Chemistry: Atomic Structure, Bonding & Amount of Substance

Vocabulary practice flashcards covering fundamental definitions, equations, shapes, and concepts across Atomic Structure, Bonding, and Amount of Substance for AQA A-Level Chemistry.

Isotopes

Atoms of the same element that have the same number of protons but different numbers of neutrons, giving identical chemical properties but slightly differing physical properties.

Relative Isotopic Mass

The mass of an isotope compared with one-twelfth of the mass of an atom of carbon-12, measured on a scale on which an atom of carbon-12 has a mass of exactly 12 units.

Relative Atomic Mass ($A_r$)

The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12.

Electron Impact Ionisation

An ionisation process where a vaporised sample is bombarded by high-energy electrons fired from an electron gun, knocking off one electron to form a single positive ion: $X_{(g)} + e^- \rightarrow X^+_{(g)} + 2e^-$.

Electrospray Ionisation

A soft ionisation technique where a sample is dissolved in a volatile polar solvent and injected through a fine hypodermic needle connected to a high-voltage supply, causing particles to gain a proton: $X_{(g)} + H^+ \rightarrow [XH]^+_{(g)}$.

Time of Flight (ToF) Acceleration

The stage in mass spectrometry where positive ions are accelerated by an electric field to give all ions a constant kinetic energy ($KE = \frac{1}{2}mv^2$), causing ion velocity to depend solely on mass.

Time of Flight (ToF) Detection

The stage where positive ions strike a negative detector plate, accept electrons, and generate an electric current with a magnitude directly proportional to the abundance of arriving ions.

Atomic Orbital

A region around the nucleus that can hold up to two electrons with opposite spins.

Aufbau Principle

The principle stating that orbitals fill in order of increasing energy ($1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p$), where the $4s$ subshell fills before $3d$ and also empties before $3d$ during ion formation.

Hund's Rule

The rule dictating that orbitals of equal energy are occupied singly before electron pairing occurs, with the singly occupying electrons having parallel spins.

First Ionisation Energy

The enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge: $X_{(g)} \rightarrow X^+_{(g)} + e^-$.

Ionic Bonding

The strong electrostatic attraction between oppositely charged ions arranged in a regular, repeating giant ionic lattice.

Covalent Bonding

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

Coordinate (Dative Covalent) Bonding

A covalent bond formed where both shared electrons in the bond originate from a single atom that donates a lone pair.

Metallic Bonding

The strong electrostatic attraction between positively charged metal ions and a surrounding delocalised sea of outer-shell electrons.

Electronegativity

The power of an atom to attract the electron density in a covalent bond towards itself, measured on the Pauling scale.

London Dispersion Forces

Weak intermolecular forces caused by temporary, instantaneous dipoles resulting from random fluctuations in electron density, which induce matching dipoles in adjacent molecules.

Hydrogen Bonding

The strongest type of intermolecular force, occurring strictly when hydrogen is covalently bonded to a highly electronegative atom with a lone pair (fluorine, oxygen, or nitrogen).

Electron Pair Repulsion Theory (VSEPR)

The theory stating electron pairs around a central atom repel each other to achieve maximum separation, with repulsion strength decreasing in the order: Lone Pair–Lone Pair > Lone Pair–Bond Pair > Bond Pair–Bond Pair.

Linear Geometry

A molecular shape characterized by 2 bonding pairs and 0 lone pairs around the central atom, giving a bond angle of $180^\circ$ (e.g., $CO_2$).

Trigonal Planar Geometry

A molecular shape characterized by 3 bonding pairs and 0 lone pairs around the central atom, giving a bond angle of $120^\circ$ (e.g., $BF_3$).

Tetrahedral Geometry

A molecular shape characterized by 4 bonding pairs and 0 lone pairs around the central atom, giving a bond angle of $109.5^\circ$ (e.g., $CH_4$).

Trigonal Pyramidal Geometry

A molecular shape characterized by 3 bonding pairs and 1 lone pair around the central atom, giving a bond angle of $107^\circ$ due to lone-pair compression (e.g., $NH_3$).

Bent (Non-linear) Geometry

A molecular shape characterized by 2 bonding pairs and 2 lone pairs around the central atom, giving a bond angle of $104.5^\circ$ (e.g., $H_2O$).

Trigonal Bipyramidal Geometry

A molecular shape characterized by 5 bonding pairs and 0 lone pairs around the central atom, giving bond angles of $90^\circ$ and $120^\circ$ (e.g., $PCl_5$).

Octahedral Geometry

A molecular shape characterized by 6 bonding pairs and 0 lone pairs around the central atom, giving bond angles of $90^\circ$ (e.g., $SF_6$).

Avogadro Constant ($L$)

The number of defined particles in one mole of a substance, with an exact value of $6.022 \times 10^{23}\,mol^{-1}$.

Ideal Gas Equation

The fundamental gas equation $pV = nRT$, relating pressure ($p$ in $Pa$), volume ($V$ in $m^3$), amount of substance ($n$ in $mol$), the ideal gas constant ($R = 8.31\,J\,K^{-1}\,mol^{-1}$), and temperature ($T$ in $K$).

Empirical Formula

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

Molecular Formula

The actual number of atoms of each element present in one molecule of a compound, calculated using: $\text{Molecular Formula} = \text{Empirical Formula} \times \left(\frac{\text{Relative Molecular Mass of Molecule}}{\text{Mass of Empirical Formula}}\right)$.

Percentage Yield

A metric evaluating experimental efficiency defined as: $\text{Percentage Yield} = \left(\frac{\text{Actual Yield}}{\text{Theoretical Yield}}\right) \times 100$.

Atom Economy

A green chemistry metric measuring reactant efficiency defined as: $\text{Atom Economy} = \left(\frac{\text{Mass of Desired Product}}{\text{Total Mass of Reactants}}\right) \times 100$.

Hydrated Salt

A crystalline salt containing a fixed stoichiometric ratio of water molecules (water of crystallisation) bound within its crystal lattice (e.g., $CuSO_4 \cdot 5H_2O$).