chemistry

Isotope

Atoms of the same element that have the same number of protons but a different number of neutrons.

Relative formula mass ($M_r$)

The sum of the relative atomic masses ($A_r$) of all the atoms in the numbers shown in the chemical formula.

Oxidation (in terms of electrons)

The loss of electrons during a chemical reaction.

Reduction (in terms of electrons)

The gain of electrons during a chemical reaction.

General formula for alkanes

$$C_n H_{2n+2}$$

Exothermic reaction

A reaction that transfers energy to the surroundings, leading to a rise in the temperature of the surroundings.

Endothermic reaction

A reaction that takes in energy from the surroundings, leading to a fall in the temperature of the surroundings.

Activation energy

The minimum amount of energy that reacting particles must possess in order to react upon collision.

Chromatography $R_f$ value formula

$$R_f = \frac{\text{distance moved by substance}}{\text{distance moved by solvent}}$$

Potable water

Water that is safe to drink because it contains sufficiently low levels of dissolved salts and microbes.

Atomic number

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

Mass number

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

Ionic bond

A strong electrostatic attraction between oppositely charged ions formed by the transfer of electrons.

Covalent bond

A shared pair of electrons between two non-metal atoms.

Metallic bond

The electrostatic attraction between positive metal ions and a sea of delocalised electrons.

Concentration formula ($g\,dm^{-3}$)

$$\text{concentration} = \frac{\text{mass of solute}}{\text{volume of solvent}}$$

Ionic equation for neutralisation

$$H^+_{(aq)} + OH^-_{(aq)} \rightarrow H_2O_{(l)}$$

Electrolysis

The process of decomposing an ionic compound in molten state or solution using electricity.

Catalyst

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

Products of complete combustion of a hydrocarbon

Carbon dioxide ($CO_2$) and water ($H_2O$).

Cracking

The thermal decomposition reaction used to break down long-chain hydrocarbons into shorter, more useful alkanes and alkenes.

Pure substance (in chemistry)

A single element or compound that is not mixed with any other substance.

Proportions of main gases in Earth's current atmosphere

Approximately $78\%$ nitrogen, $21\%$ oxygen, and small proportions of argon, carbon dioxide, and water vapour.

Phytomining

A method of copper extraction that uses plants to absorb copper compounds from low-grade ores before the plants are harvested and burned.

Gas test for hydrogen gas

A burning splint held near the open end of a test tube produces a squeaky pop sound.

Gas test for oxygen gas

A glowing splint inserted into a test tube relights.

Gas test for carbon dioxide gas

Bubbling the gas through an aqueous solution of calcium hydroxide (limewater) turns the limewater cloudy.

Gas test for chlorine gas

Damp litmus paper placed into the gas is bleached and turns white.

Mean rate of reaction formula (in terms of reactant used)

$$\text{Mean rate of reaction} = \frac{\text{quantity of reactant used}}{\text{time taken}}$$

Chemical test to distinguish between an alkane and an alkene

Bromine water turns from orange to colourless when mixed with an alkene, but remains orange when mixed with an alkane.

Formulation

A complex mixture that has been designed as a useful product, where each component is present in a specific, measured quantity.

Bioleaching

A method of metal extraction that uses bacteria to produce leachate solutions containing soluble metal compounds from low-grade ores.

Reactivity trend down Group 1 (Alkali metals)

Reactivity increases down the group because the outer electron is further from the nucleus, experiencing weaker attraction and being lost more easily.

Reactivity trend down Group 7 (Halogens)

Reactivity decreases down the group because the outer shell is further from the nucleus, making it harder to attract and gain an electron.

Dynamic equilibrium

A state in a reversible reaction inside a closed system where the forward and reverse reactions occur at the exact same rate, keeping concentrations constant.

Fractional distillation of crude oil

A process that separates crude oil into fractions containing hydrocarbons with similar chain lengths and boiling points.

Graphene

A single layer of carbon atoms arranged in hexagonal rings, exactly one atom thick.

Fullerene ($C_{60}$)

A spherical molecule made of carbon atoms arranged in hexagonal and pentagonal rings, useful in drug delivery systems and lubricants.

Limiting reactant

The reactant that is completely used up in a chemical reaction, which stops the reaction and limits the amount of product formed.

Noble gases (Group 0) unreactivity

They are unreactive because their atoms have a stable, full outer shell of electrons.

Structural features of diamond

A giant covalent structure where each carbon atom forms four strong covalent bonds, making it extremely hard with a high melting point.

Electrical conductivity in graphite

Graphite conducts electricity because each carbon atom forms three bonds, leaving one delocalised electron per atom free to move throughout the structure and carry charge.

Law of conservation of mass

No atoms are created or destroyed during a chemical reaction, so the total mass of the products is equal to the total mass of the reactants.

Displacement reaction

A reaction in which a more reactive element takes the place of a less reactive element in its compound.

General equation for the reaction of a metal with an acid

$$\text{Metal} + \text{Acid} \rightarrow \text{Salt} + \text{Hydrogen}$$

General equation for the reaction of an acid with a metal carbonate

$$\text{Acid} + \text{Metal Carbonate} \rightarrow \text{Salt} + \text{Water} + \text{Carbon Dioxide}$$

Product formed at the cathode during electrolysis of an aqueous solution

Hydrogen gas is produced if the metal is more reactive than hydrogen; otherwise, the metal element itself is produced.

Collision theory

Chemical reactions occur only when reacting particles collide with each other with sufficient energy equal to or greater than the activation energy.

Le Chatelier's Principle

If a system at equilibrium is subjected to a change in conditions, the system shifts to counteract that change.

Trend in boiling point as alkane chain length increases

Boiling point increases because larger molecules have stronger intermolecular forces that require more energy to overcome.

Mechanism of the greenhouse effect

Greenhouse gases absorb longer wavelength infrared radiation emitted from the Earth's surface and re-radiate it in all directions, trapping heat in the atmosphere.

Carbon footprint

The total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service, or event.

Life Cycle Assessment (LCA)

An evaluation of the environmental impact of a product carried out across four stages: extracting raw materials, manufacturing and packaging, use during its lifespan, and disposal.

Desalination methods for producing potable water from sea water

Distillation and reverse osmosis, both of which require large amounts of energy.