AQA GCSE Chemistry Unit 2 Definitions

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  • Created by: Bryony
  • Created on: 15-05-13 09:45
Contains protons, neutrons and electrons
Atom
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Total number of protons and neutrons
Mass Number
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Number of protons
Atomic Number
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Different atomic forms of the same element, which have the same number of protons but a different number of neutrons
Isotope
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When atoms lose or gain electrons to form charged particles
Ionic Bonding
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Always have giant ionic lattices, have high melting and boiling points and carry and electric current when melted. They also dissolve easily in water.
Ionic Compounds
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Where atoms share electrons in their outer shells so both atoms have a full outer shell.
Covalent Bonds
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When the atoms form very strong covalent bonds to form small molecules, however the forces between the molecules are very weak and they don't conduct electricity.
Simple Molecular Structures
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All the atoms are bonded together by very strong covalent bonds, so have very high melting and boiling points. They don't conduct electricity even when molten.
Giant Covalent Structures (Macromolecules)
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A chemical bond where electrons are shared across lots of nuclei, this enables it to conduct electricity. It is also maleable and a good conducter of heat.
Metallic Bonds
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A metal made by combining two or more metallic elements to give greater strength or resistance to corrosion.
Alloys
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The properties can be changed by the external condition, like light, tempreture, pressure or electricit. The change is reversible and repeatable.
Smart Materials
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A nanoscale particle, contains a few hundred atoms (includeing fullerenes) and have a huge surface area to volume ratio
Nanoparticles
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Substance built from long chains of atoms held together by covalent bonds, may have crosslinks between molecules to increase strength
Polymers
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Individual tangled chainsof polymers, held toghther by weak intermolecular forces so are free to slide over each other, low melting point
Thermosoftening Polymers
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Has strong intermolecular forces between polymers which holds it in a solid structure, strong, hard, rigid
Thermosetting Polymers
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Made by heating ethene to 200C under high pressure, used for bags and bottles
Low Density Polythene
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Made from ethene at a low tempreture and pressure with a catalyst, rigid, used for water tanks and drainpipes
High Density Polythene
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How heavy different atoms are compared with the mass of an atom of carbon-12
Relative Atomic Mass (Ar)
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All the relative atomic masses added together
Relative Formula Mass (Mr)
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The relative formula mass of a substance in grams
One mole
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Mass in grams of element or compound divided by the relative formula mass of the element or compound
Number of moles
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Ar x the number of elements divided by the Mr of the whole compound x 100
Percentage mass of an element in a compound
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List all the elements, write the experimental masses or percentages underneath, divide each mass by the Ar, give this ratio in it's simplest ratio
Empirical Formula
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Write out the balanced equation, work out the Mr for the two bits you want and divide to get 1g and times to get the amount needed
Calculating masses in reactions
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Actual yield in grams divided by the predicted yield in grams x 100
Percentage yield
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Where the products of the reaction can themselves react to produce the original reactants
Reversible reaction
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Can be separated by using paper chromatography
Artificial colours e.g.food colouring
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advantages of using these are that they are very sensitive, very fast and very accurate
Instrumental methods (machines)
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Used to identify substances by producing a graph, by reading off the molecular ion peak the relative molecular mass can be found.
Gas Chromatography
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Amount of reactant used or product formed divided by time
The rate of reaction
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This depends on temperature, concentration (or pressure for gases), catalyst and the surface area of solids
The rate of reaction
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Can be measured by the amount of precipitation, the change in mass (usually a gas) or the volume of gas given off
The rate of reaction
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Depends on how often and how hard the reacting particles collide with each other, can be increased by a higher temperature, a higher concentration (or pressure) or a larger surface area
Collision Theory
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The energy an atom must have before a process/reaction can take place.
Activation Energy
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A substance that speeds up a reaction, without being changed or used up in the reaction.
Catalyst
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A reaction that transfers energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature. Example: Combustion
Exothermic Reaction
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A reaction that takes in energy from it's surroundings, usually in the form of heat and usually shown by a fall in temperature. Example: Thermal Decomposition
Endothermic Reaction
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A measure of how acidic or alkaline a solution is, ranges from 0 to 14
The pH scale
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A dye that changes colour when added to a solution depending on whether it is above or below a certain pH
Indicator
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A substance with a pH of less than 7, forms H+ ions in water
Acid
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A substance with a pH greater than 7.
Base
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A base that dissolves in water, forms OH- ions in water
Alkali
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Acid + Base -> Salt + Water or H+ (aq) +OH- (aq) -> H2O (l)
Formula for neutralisation
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State symbol for 'dissolved in water'
(aq)
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Acid + Metal -> Salt + Hydrogen
Formula for acids reacting with metals
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Will always produce chloride salts (HCl)
Hydrochloric Acid
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Will always produce sulphate salts (H2SO4)
Sulphuric Acid
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Will produce nitrate salts when neutralised, nitrates when reacted with alkalis and nitrogen oxides with metals
Nitric Acid
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Acid + Metal Oxide -> Salt + Water
Formula for acids reacting with metal oxides
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Acid + Metal Hydroxide -> Salt + Water
Formula for acids reacting with metal hydroxides
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Ammonia + Nitric acid -> Ammonium nitrate This is a good fertiliser because it has nitrogen from the ammonia and the nitric acid (plants need nitrogen to make proteins)
Ammonium Nitrate
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Add the metal, metal oxide or hydroxide to the acid, the solid will dissolve as it reacts and any excess solid will just sink to the bottom. Then filter out the excess metal, metal oxide or metal hydroxide to get the salt solution. Evaporate.
Making soluble salts using a metal or an insoluble base
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Add indicator to the acid. Then add alkali drop by drop until neutralised. Then repeat with the exact amounts without the indicator so the salt isn't contaminated. Evaporate.
Making soluble salts using an alkali
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Pick two solutions that contain the ions needed. Mix, then filter and dry on filter paper.
Making insoluble salts
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Can be used to remove poisonous ions from water and when treating sewage (again, to remove unwanted ions).
Precipitation Reactions
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Chemical decomposition produced by passing an electric current through a liquid or solution containing ions
Electrolysis
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Oxidation Is Loss, Reduction Is Gain
OIL RIG
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In this reaction the sodium ions stay in the solution because they are more reactive than hydrogen
Electrolysis of Sodium Chloride Solution
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2H+ + 2e- --> H2
Half-equation at the negative electrode in the Electrolysis of a Sodium Chloride Solution
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2Cl- --> Cl2 + 2e- or 2Cl- - 2e- --> Cl2
Half-equation at the positive electrode in the Electrolysis of a Sodium Chloride Solution
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Al2O3
Pure Aluminium Oxide
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Used to lower the temperature and costs of the Electrolysis of Aluminium
Cryolite
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Al3+ + 3e- --> Al
Half-equation at the negative electrode in the Electrolysis of Aluminium
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2O2- --> O2 + 4e-
Half-equation at the positive electrode in the Electrolysis of Aluminium
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Using electrolysis to cover the surface of one metal with another metal
Electroplating
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Decoration and conduction
Uses for electroplating
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Other cards in this set

Card 2

Front

Mass Number

Back

Total number of protons and neutrons

Card 3

Front

Atomic Number

Back

Preview of the back of card 3

Card 4

Front

Isotope

Back

Preview of the back of card 4

Card 5

Front

Ionic Bonding

Back

Preview of the back of card 5
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