Topic 1: Atoms, Formulae and Calculations

Comprehensive vocabulary flashcards covering key definitions, symbols, and concepts from Topic 1 (Atoms, Elements, Equations, Reacting Masses, Yield, Empirical Formulae, Gas Laws, and Solution Concentrations).

Atom

The smallest part of an element that has the properties of that element, composed of protons, neutrons, and electrons.

Element

A chemically simple substance that contains atoms of only one type and cannot be broken down using chemical reactions.

Molecule

A particle made of two or more atoms bonded together.

Compound

A substance containing atoms of different elements combined together.

Ion

A species consisting of one or more atoms joined together and having a positive or negative charge.

Cation

An ion with a positive charge.

Anion

An ion with a negative charge.

Monatomic

Describing elements or ions that are made up of single atoms, such as helium ($\text{He}$) or chloride ($\text{Cl}^-$).

Diatomic

Describing elements, compounds, or ions made up of two atoms joined together, such as nitrogen ($\text{N}_2$) or hydroxide ($\text{OH}^-$).

Polyatomic

Describing elements, compounds, or ions with molecules or units made up of several atoms joined together, such as methane ($\text{CH}_4$) or sulfate ($\text{SO}_4^{2-}$).

Coefficient

The technical term for the number written in front of species when balancing a chemical equation.

Spectator Ion

An ion that is present both before and after a reaction but is not involved in the reaction.

Displacement Reaction

A reaction in which one element replaces another, less reactive, element in a compound.

Precipitation Reaction

A reaction in which an insoluble solid is formed when two solutions are mixed.

Relative Atomic Mass ($A_r$)

The weighted mean (average) mass of an atom of an element compared to $\frac{1}{12}$ of the mass of an atom of $^{12}\text{C}$.

Relative Molecular Mass ($M_r$)

The sum of the relative atomic masses of the atoms in a molecule, used for molecules of elements and compounds.

Relative Formula Mass ($M_r$)

The sum of the relative atomic masses of all atoms present in a given chemical formula, including molecular and giant ionic structures.

Molar Mass ($M$)

The mass per mole of a substance, represented by the symbol $M$ and having the units $\text{g\,mol}^{-1}$.

Avogadro Constant ($L$)

$6.02 \times 10^{23}\,\text{mol}^{-1}$, which represents the number of particles (atoms, molecules, or ions) in one mole of any substance.

Mole (mol)

The amount of substance that contains the same number of particles as the number of carbon atoms in exactly $12\,\text{g}$ of the $^{12}\text{C}$ isotope.

Hydrate

A compound containing water of crystallisation, represented by formulae such as $\text{CuSO}_4 \cdot 5\text{H}_2\text{O}$.

Theoretical Yield

The maximum possible mass of a product in a reaction, calculated assuming complete reaction and no losses.

Actual Yield

The actual mass of a product obtained in a reaction, determined by weighing rather than calculation.

Percentage Yield

The actual yield divided by the theoretical yield, expressed as a percentage: $\frac{\text{actual yield}}{\text{theoretical yield}} \times 100\%$.

Atom Economy

A measure of the efficiency of a reaction calculated as $\frac{\text{molar mass of desired product}}{\text{sum of molar masses of all products}} \times 100\%$.

Empirical Formula

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

Molecular Formula

The actual number of atoms of each element present in a molecule of a compound.

Ideal Gas Equation

The relation $pV = nRT$, where $p$ is pressure in $\text{Pa}$, $V$ is volume in $\text{m}^3$, $n$ is amount in $\text{mol}$, $R$ is the gas constant ($8.31\,\text{J\,mol}^{-1}\text{K}^{-1}$), and $T$ is temperature in $\text{K}$.

Molar Volume ($V_m$)

The volume occupied by $1\,\text{mol}$ of any gas, which is approximately $24\,\text{dm}^3\,\text{mol}^{-1}$ (or $24\,000\,\text{cm}^3\,\text{mol}^{-1}$) at room temperature and pressure (r.t.p.).

Solute

A substance that is dissolved in a solvent.

Solvent

A substance that dissolves a solute.

Solution

A homogeneous mixture formed when a solute dissolves in a solvent.

Mass Concentration

The mass (in $\text{g}$) of a solute divided by the volume (in $\text{dm}^3$) of the resulting solution, with units of $\text{g\,dm}^{-3}$.

Molar Concentration

The amount (in $\text{mol}$) of a solute divided by the volume (in $\text{dm}^3$) of the solution, with units of $\text{mol\,dm}^{-3}$.

Parts Per Million (ppm)

The number of parts of one substance in one million parts of another substance, commonly used as a measure of chemical concentration based on mass or volume.

Parts Per Million by Volume (ppmv)

A unit of concentration for gases indicating volume comparison, where $1\,\text{ppmv}$ represents $1\,\text{cm}^3$ of gas per $1\,000\,000\,\text{cm}^3$ (or $1\,000\,\text{dm}^3$) of air.