GCSE Combined Science - Chemistry

Acid

a substance with a pH of less than 7 that forms H+ ions in water

activation energy

the minimum amount of energy that reactant particles must have when they collide in order to react

alkali

a substance with a pH greater than 7 that forms OH- ions in solution

alkali metal

an element in group 1 of the periodic table

alkane

a saturated hydrocarbon with the general formula CnH2n+2

alkene

a type of hydrocarbon that is more reactive than alkanes

alloy

a metal that is a mixture of two or more metals, or a mixture involving metals and non-metals

anion

a particle with a negative charge, formed when one or more electrons are gained

anomalous result

a result that doesn't fit with the rest of the data

aqueous

when a substance is in solution with water

atmosphere

the layer of air that surrounds a planet

atom

a neutral particle made up of protons and neutrons in the nucleus, with electrons surrounding the nucleus

atomic number

the number of protons in the nucleus of an atom. proton number

avogadro constant

the number of particles in one mole of a substance, 6.02 x 10^23

base

a substance that reacts with acids in neutralisation reactions

boiling

the transition of a substance from a liquid to a gas

boiling point

the temperature at which a substance changes from a liquid to a gas or gas to liquid

bond energy

the amount of energy required to break a bond or the amount of energy released when a bond forms

calibrate

measure something with a known quantity and set the instrument being used to that quantity

carbon footprint

a measure of the amounts of greenhouse gases released by a product, service or event

catalyst

a substance that can speed up a reaction without being changed or used up

cracking

the process of breaking down long-chain hydrocarbons into shorter ones using a catalyst, often aluminium oxide

categoric data

data that comes in distinct categories

cation

a particle with a positive charge formed when one or more electrons are lost

chemical bond

the attraction of two atoms for each other, caused by the sharing or transfer of electrons

chromatogram

the pattern of spots formed as a result of separating a mixture using chromatography

chromatography

an analytical method used to separate the substances in a mixture based on how the components interact with a mobile phase and a stationary phase

climate change

a change in the Earth's climate

collision theory

the theory that in order for a reaction to occur particles must collide with sufficient energy

combustion

an exothermic reaction between a fuel and oxygen

compound

a substance made up of atoms of at least two different elements, chemically joined together

concentration

the amount of a substance in a certain volume of solution

condensing

the transition of a substance from a gas to a liquid

continuous data

numerical data that can have any value within a range

control group

a group that matches the one being studied, but where the independent variable isn't altered.

control variable

a variable in an experiment that is kept the same

conversion factor

a number which you must multiply or divide a unit by to convert it to a different unit

correlation

a relationship between two variables

covalent bond

a chemical bond formed when atoms share a pair of electrons

covalent substance

a substance where the atoms are held together by covalent bonds

crystallisation

the formation of solid crystals as water evaporates from a solution

delocalised electron

an electron that isn't associated with a particular atom or bond and is free to move within a structure

dependent variable

the variable in an experiment that is measured

displacement reaction

a reaction where a more reactive element replaces a less reactive element in a compound

displayed formula

a chemical formula that shows the atoms in a covalent compound and all the bonds between them

distillation

a way of separating out a liquid from a mixture. you heat the mixture until the liquid evaporates, then cool and condense it.

double covalent bond

two pairs of electrons shared between two atoms

electrode

an electrical conductor which is submerged in the electrolyte during electrolysis

electrolysis

the process of breaking down a substance using electricity

electrolyte

a liquid or solution used in electrolysis to conduct electricity between the two electrodes

electron

a subatomic particle with a relative charge of -1

electron - location

in shells surrounding he nucleus of an atom

electron shell

a region of an atom that contains electrons

energy level

a region of an atom that contains electrons of a particular energy

electronic structure

the number of electrons in an atom (or ion) of an element and how they are arranged

electrostatic force

a force of attraction between opposite charges

element

a substance that is made up only of atoms with the same number of protons

endothermic reaction

a reaction which takes in energy from the surroundings

energy level diagram

a graph that shows how the energy in a reaction changes as the reaction progresses

enzyme

a biological catalyst

equilibrium

the point at which the rates of the forward and backward reactions in a reversible reaction are the same, so the amount of reactants and products don't change

evaporation

the process where a liquid changes into a gas.

exothermic reaction

a reaction which transfers energy to the surroundings

Fair test

a controlled experiment where the only thing that changes is the independent variable.

Feedstock

a raw material used to produce other substances through industrial processes.

Filtration

A physical method used to separate an insoluble solid from a liquid

Finite resource

a resource that isn't replaced at a quick enough rate to be considered replaceable.

Flammability

how easy it is to ignite a substance

Formulation

a useful mixture with a precise purpose made by following a formula

Fraction

a group of hydrocarbons that condense together when crude oil is separated using fractional distillation

Fraction e.g.

petrol, naphtha, kerosene

Fractional distillation

a process that can be used to separate the substances in a mixture according to their boiling points

Freezing

the transition of a substance from a liquid to a solid

Frequency density

the height of a bar on a histogram. It is found by the frequency divided by class width.

Gas - forces of attraction

weak

Gas - particle motion

free to move in random directions

Gas

no fixed volume or shape

General formula

a formula that can be used to find the molecular formula of any member of a homologous series

Giant covalent structure

a large molecule made up of a very large number of atoms held together by covalent bonds (macromolecule)

Global warming

the increase in the average temperature of the Earth

Greenhouse effect

when greenhouse gases int he atmosphere absorb long wavelength radiation and re-radiate it in all directions, including back towards Earth, helping to keep the Earth warm

Greenhouse gas

a gas that can absorb long wavelength radiation

Group

a column in the periodic table

Half equation

An equation which shows how electrons are transferred when a substance is reduced or oxidised

Halide ion

An ion with a 1- charge formed when a halogen atom gains an electron

Halogen

An element in Group 7 of the periodic table.

Hazard

something that has the potential to cause harm

Homologous series

a group of chemical that react in a similar way because they ahve the same functional group.

Hydrocarbon

a compound that is made from only hydrogen and carbon

Hypothesis

a possible explanation for a scientific observation

Incomplete combustion

when a fuel burns but there isn't enough oxygen for it to burn completely

Incomplete combustion - products

include carbon monoxide and carbon particulates

Independent variable

The variable in an experiment that is changed

Indicator

a substance that changes colour above or below a certain pH

Insoluble

a substance that does not dissolve in a particular solvent

Intermolecular force

a force of attraction that exists between molecules

Ion

a charged particle formed when on or more electrons are lost of gained from an atom or molecule

Ionic bond

a strong attraction between oppositely charged ions

Ionic compound

a compound that contains positive and negative ions held together in a regular arrangement (a lattice) by electrostatic forces of attraction

Ionic equation

an equation that shows only the particles that react and the products they form