AQA A-Level Chemistry Year 1 & AS Vocabulary

Vocabulary flashcards covering core concepts, chemical terms, definitions, and equations across AQA A-Level Chemistry Year 1 and AS topics.

Atom

The smallest particle of an element that retains the characteristic chemical properties of that element.

Atomic Number ($Z$)

The number of protons in the nucleus of an atom of an element.

Mass Number ($A$)

The total number of protons and neutrons in the nucleus of an atom.

Isotopes

Atoms of the same element with the same number of protons (same atomic number) but a different number of neutrons (different mass number).

Relative Isotopic Mass

The mass of a single isotope of an element relative to $\frac{1}{12}$ the mass of an atom of carbon-12.

Relative Atomic Mass ($A_r$)

The average mass of an atom of an element relative to $\frac{1}{12}$ the mass of an atom of carbon-12.

Relative Molecular Mass ($M_r$)

The mass of a molecule relative to $\frac{1}{12}$ the mass of an atom of carbon-12.

First Ionisation Energy

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous $1+$ ions.

Isoelectronic

Describes particles that possess the exact same electron configuration.

Empirical Formula

A chemical formula showing the simplest whole-number ratio of the atoms of each element present in a compound.

Molecular Formula

A chemical formula showing the actual number of atoms of each element present in one molecule of a compound.

Spectator Ions

Ions in an ionic reaction mixture that do not take part in the chemical reaction and remain unchanged on both sides of the equation.

Avogadro Constant ($L$)

The number of atoms in $12.000\,\text{g}$ of carbon-12, equal to $6.02 \times 10^{23}\,\text{mol}^{-1}$.

Mole

The amount of a substance that contains the Avogadro constant ($6.02 \times 10^{23}$) number of specified particles (atoms, molecules, ions, or electrons).

Percentage Yield

The percentage of the theoretical yield obtained experimentally, calculated as $\frac{\text{actual yield}}{\text{theoretical yield}} \times 100$.

Atom Economy

A measure of the efficiency of a chemical reaction, calculated as $\frac{\text{molecular mass of desired product}}{\text{sum of molecular masses of all reactants}} \times 100$.

Standard Solution

A solution of accurately known concentration used in volumetric analysis.

Concordant Titres

Titre values from a titration experiment that are within $0.10\,\text{cm}^3$ of each other.

Ionic Bond

The electrostatic attraction between oppositely charged ions in a chemical compound.

Covalent Bond

A chemical bond formed by a shared pair of electrons between two non-metal atoms.

Coordinate Bond (Dative Covalent Bond)

A covalent bond in which both electrons in the shared pair are donated by a single atom.

Metallic Bond

The electrostatic attraction between positive metal ions and the sea of delocalised electrons in a metallic lattice.

Electronegativity

The power of an atom to attract the pair of electrons in a covalent bond towards itself.

Polar Covalent Bond

A covalent bond between two atoms with different electronegativities, causing an unequal distribution of electron density and partial charges ($\delta+$ and $\delta-$).

Hydrogen Bond

An intermolecular force occurring between a $\delta+$ hydrogen atom covalently bonded to an electronegative atom ($\text{O}$, $\text{N}$, or $\text{F}$) and a lone pair of electrons on an $\text{O}$, $\text{N}$, or $\text{F}$ atom of an adjacent molecule.

Van der Waals' Forces

Weak intermolecular attractive forces existing between all atoms and molecules, caused by temporary, instantaneous, and induced dipoles.

Enthalpy ($H$)

A thermodynamic property of a system linked to internal energy, relating to the energy of the bonds broken and made during a chemical reaction.

Enthalpy Change ($\Delta H$)

The heat energy change of a reaction measured at constant pressure, given by $\Delta H = H_{\text{products}} - H_{\text{reactants}}$.

Activation Energy ($E_a$)

The minimum amount of energy required by colliding reactant particles for a successful chemical reaction to occur.

Standard Enthalpy of Formation ($\Delta_f H^\ominus$)

The enthalpy change when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.

Standard Enthalpy of Combustion ($\Delta_c H^\ominus$)

The enthalpy change when one mole of a substance is burned completely in excess oxygen with all reactants and products in their standard states under standard conditions.

Hess's Law

States that the overall enthalpy change for a chemical reaction is independent of the route taken and depends only on the initial and final states.

Mean Bond Enthalpy

The energy required to break one mole of a specific covalent bond measured in the gaseous state, averaged across many different compounds containing that bond.

Rate of Reaction

The change in concentration of a reactant or product in a given period of time.

Catalyst

A substance that increases the rate of a chemical reaction without being used up, by providing an alternative reaction pathway with a lower activation energy.

Maxwell–Boltzmann Distribution

A plot showing the distribution of molecular energies among gaseous molecules at a fixed temperature.

Dynamic Equilibrium

A reversible system where the concentrations of reactants and products remain constant, and the forward and reverse reactions proceed at equal rates.

Homogeneous Reaction

A chemical reaction in which all reactants and products are in the same physical state.

Le Chatelier's Principle

States that if a system at equilibrium is disturbed by changing a factor (such as temperature, pressure, or concentration), the position of equilibrium will move in a direction so as to oppose the change.

Equilibrium Constant ($K_c$)

A constant value representing the ratio of product concentrations to reactant concentrations raised to their stoichiometric powers for a homogeneous system at a constant temperature.

Oxidation State

A numerical value representing the degree of oxidation or reduction of an atom in a compound, defined as the hypothetical charge assuming completely ionic bonding.

Oxidation

A chemical process involving the loss of electrons, an increase in oxidation state, or the gain of oxygen / loss of hydrogen.

Reduction

A chemical process involving the gain of electrons, a decrease in oxidation state, or the loss of oxygen / gain of hydrogen.

Redox Reaction

A chemical reaction in which both oxidation and reduction occur simultaneously.

Oxidising Agent

A substance that accepts electrons from another species, causing that species to be oxidised while itself becoming reduced.

Reducing Agent

A substance that donates electrons to another species, causing that species to be reduced while itself becoming oxidised.

Periodicity

The repeating pattern of physical and chemical properties of elements across periods in the Periodic Table.

Hydrocarbon

An organic compound composed exclusively of carbon and hydrogen atoms.

Saturated Hydrocarbon

A hydrocarbon containing only single covalent bonds between carbon atoms.

Unsaturated Hydrocarbon

A hydrocarbon containing at least one carbon–carbon double bond ($\text{C=C}$) or multiple bond.

Functional Group

An atom or group of atoms in an organic molecule responsible for its characteristic chemical reactions.

Homologous Series

A family of organic compounds sharing the same general formula, functional group, and similar chemical properties, with successive members differing by a $-\text{CH}_2-$ unit.

Displayed Formula

A chemical formula that shows every atom and every covalent bond in a molecule.

Structural Formula

A formula showing the arrangement of atoms carbon by carbon, with attached hydrogens and functional groups, without showing all the bonds.

Skeletal Formula

A simplified organic formula showing only the carbon skeleton as lines and any functional groups or non-carbon atoms, omitting carbon and hydrogen atoms bonded to carbons.

Structural Isomers

Molecules that share the same molecular formula but have different structural formulae.

Stereoisomers

Molecules with the same molecular and structural formula but a different three-dimensional arrangement of their atoms in space.

$E\text{--}Z$ Isomerism

A form of stereoisomerism in alkenes resulting from restricted rotation around the planar $\text{C=C}$ double bond, named $Z$ (high priority groups on the same side) or $E$ (high priority groups on opposite sides).

Fractional Distillation

The continual evaporation and condensation of a liquid mixture in a fractionating column to separate it into fractions based on differences in boiling points.

Cracking

An industrial process in which long-chain alkane molecules are broken down into shorter-chain, more useful alkanes and alkenes.

Thermal Cracking

High-temperature ($1000\text{--}1200\,\text{K}$) and high-pressure ($70\,\text{atm}$) cracking of alkanes for a short time to produce a high proportion of alkenes.

Catalytic Cracking

Cracking of alkanes carried out at $800\text{--}1000\,\text{K}$ and $1\text{--}2\,\text{atm}$ pressure using a zeolite catalyst to produce branched alkanes, cycloalkanes, and aromatic compounds.

Free Radical

A highly reactive neutral atom or group of atoms possessing an unpaired electron.

Substitution Reaction

A chemical reaction in which an atom or group of atoms in a molecule is replaced by a different atom or group of atoms.

Homolytic Fission

The breaking of a covalent bond where each bonded atom retains one electron from the shared pair, forming two free radicals.

Heterolytic Fission

The breaking of a covalent bond where both electrons from the shared pair move to one of the atoms, forming a positive ion and a negative ion.

Nucleophile

An electron pair donor that is attracted to an electron-deficient ($\delta+$) carbon atom.

Electrophile

An electron pair acceptor that is attracted to an area of high electron density, such as a $\text{C=C}$ double bond.

Carbocation

An organic intermediate containing a positively charged carbon atom.

Reflux

The continuous boiling and condensing of a reaction mixture to prevent the loss of volatile reactants or products.

Elimination Reaction

A reaction in which a small molecule (such as $\text{H}_2\text{O}$ or $\text{HX}$) is removed from an organic compound, forming a double bond.

Addition Polymerisation

A reaction in which unsaturated monomer molecules join together by opening their double bonds to form a long-chain polymer without forming any other products.

Dehydration Reaction

An elimination reaction in which a molecule of water is removed from an organic compound, such as converting an alcohol to an alkene.

Biofuel

A renewable fuel derived from living organisms or their waste material, such as bioethanol produced by fermentation.

Carbon-Neutral Activity

An activity or process that results in no net annual emissions of carbon dioxide into the atmosphere.

Fingerprint Region

The complex region of an infrared spectrum below $1500\,\text{cm}^{-1}$ that is unique to a specific organic molecule.