Fiches Chimie GCSE : 45 termes clés, pour Brainlag Flashcards et Anki

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Chaque réponse reprend mot pour mot une leçon gratuite de Brainlag Learn, où l'idée est expliquée en entier. Les organismes d'examen formulent certaines définitions autrement : compare avec ton programme.

Element

Has only one type of atom

Compound

Has two or more elements chemically combined in fixed proportions

Mixture

Has two or more substances not chemically joined

Filtration

An insoluble solid from a liquid (sand from water).

Crystallisation

A soluble solid from its solution: heat to evaporate some water, cool, filter off the crystals, dry them.

Simple distillation

A liquid from a solution (pure water from sea water).

Fractional distillation

Liquids with different boiling points. The one with the lowest boiling point reaches the top of the column first.

Paper chromatography

The soluble substances in a mixture, such as the dyes in an ink.

Atomic number

The number of protons.

Mass number

Protons + neutrons.

Isotopes

Are atoms of the same element with different numbers of neutrons

Ions

Have gained or lost electrons

Period

The number of occupied electron shells.

Group

The number of electrons in the outer shell.

Group 0

(noble gases) have full outer shells, so they are unreactive.

Group 1

(alkali metals) have one outer electron, which they lose to form 1+ ions.

Giant ionic lattice

Huge numbers of positive and negative ions sit in a regular three-dimensional pattern

Covalent bond

They share a pair of electrons: one from each atom.

Pure substance

A single element or a single compound with nothing else mixed in.

Formulation

A mixture designed as a useful product.

Reactivity series

Listing metals from most to least reactive

Oxidation

Gain of oxygen.

Reduction

Loss of oxygen.

Redox

A reaction in which one substance is oxidised and another is reduced

Spectator ions

An ionic equation leaves them out and shows only the particles that change.

Test for hydrogen

Hold a lit splint at the mouth of the tube: a squeaky pop.

Resolution

The smallest change an instrument shows.

Random errors

Scatter readings; repeats and means reduce them.

Systematic errors

Shift every reading the same way, such as a balance that is not zeroed (a zero error).

Precise

Repeats close together.

Accurate

Close to the true value.

Repeatable

Same person, same method agrees.

Reproducible

Others get the same.

Exothermic

Energy is transferred to the surroundings, so the temperature of the surroundings rises.

Endothermic

Energy is taken in from the surroundings, so the temperature falls.

Hydrocarbons

Compounds made of hydrogen and carbon atoms only.

Homologous series

A family with the same general formula, where each member has one more CH2 than the last, and all react in similar ways.

Saturated

Every carbon to carbon bond is a single bond.

Complete combustion

Oxidises the carbon to carbon dioxide and the hydrogen to water

Incomplete combustion

Also makes carbon monoxide (a toxic gas you cannot see or smell) and carbon (soot).

Cracking

Breaks long alkanes into shorter, more useful alkanes and alkenes.

Law of conservation of mass

The total mass of the products equals the total mass of the reactants.

Carbon footprint

The total greenhouse gas emitted over the life cycle of a product, service or event.

Greenhouse gases

(carbon dioxide, methane, water vapour) absorb infrared and re-emit it in all directions

Tangent

A straight line that touches the curve at that point without cutting it.