C2 revision

C2 revisionRevision PowerPoint for EDEXCEL Chemistry Unit 2

Periodic TableMendeleev created the periodic table as we know it in 1871. He arranged elements in order of their properties leaving gaps where he thought there should be other elements.This was found to be correct when other elements that were discovered filled these blanks.He arranged them by the following properties:

Atomic mass Density Melting Point Formula of the oxide

Patterns emerged down the groups and across the periods which confirmed his predictions.Structure of the atomAtoms are made up of PROTONS, NEUTRONS and ELECTRONS.They are found in the positions shown on the diagram.Electron shellsNucleus containing protons and neutronsParticleRelative MassRelative ChargeProton1+1Neutron10Electron1/1840-1Electrons fill shells from the middle in the order of2, 8, 8, 18 (how many elements are in each period)Data from SymbolsTop number MASS NUMBERThe number of protons and neutronsBottom number ATOMIC NUMBERThe number of protons (also the same as electrons)

Al2713Protons = 13Electrons = 13Neutrons = 27-13 = 14Protons and neutrons are packed together tightly in the nucleus (high density)Electrons are spread out in shells (low density) Electronic ConfigurationIonic BondingIonic bonds form between METALS and NON-METALS.Ionic bonding involves the transfer of ELECTRONS.Metallic Ions are POSITIVELY charged (ANIONS).Non-metallic elements are NEGATIVELY charged (CATIONS).

Loose electron+Common IonsPage 128 of the text book

Properties of Ionic compoundsConduct electricity when MOLTEN (melted) and in an AQUEOUS SOLUTION (dissolved in water)DO NOT conduct electricity as a SOLIDHave high MELTING and BOILING pointsUsually SOLID at ROOM TEMPERATURESolubility and PrecipitatesPrecipitates are SALTS that are formed in chemical reactions that DO NOT DISSOLVE in the solvent used in the reaction.

Ion TestsIon tests for metals (ANIONS) are usually done by FLAME TESTS.Each ION produces a certain flame colour.Testing for CATIONS is done through chemical testing.

Chloride add nitric acid and silver nitrate, if a white precipitate forms then chloride ions are present.

Sulphate add hydrochloric acid and barium chloride, if a white precipitate forms then sulphate ions are present.

Carbonate add an acid and if the gas produced turns limewater MILKY the carbonate ions were present.(carbonate release carbon dioxide)Covalent BondingCovalent bonds are usually between 2 non-metals. They are strong bonds.They involve the sharing of electrons (shown by dot cross diagrams)

Properties of Covalent CompoundsSimple CovalentSmall molecules oxygen gas, carbon dioxideLow melting and boiling points due to WEAK bonds between molecules.Giant Covalent Giant moleculesHigh melting and boiling points due to lots of strong bonds in the moleculeDiamond and GraphiteHardSoftGiant StructureLayers

Miscible or ImmiscibleMiscible substances mix together easily.They are separated by (FRACTIONAL) DISTILLATION or CHROMATOGRAPHY.

Immiscible substances do not mix together.They are like oil (low density) and water (high density).They are separated suing a SEPARATING FUNNEL.Metallic Bonding

Conduct electricity due to the sea of free electronsMalleable (hammer into shape) due to layers that can slip over each otherAlkali MetalsReact with water to form a HYDROXIDE (OH-)More reactive down the group (easier to loose the outside electron)1 electron in outer shell (+1 ion)Increase in density down the group

http://www.youtube.com/watch?v=uixxJtJPVXk

HalogensFluorine pale greenChlorine pale yellowBromine brown liquid, orange vapourIodine Grey solid, purple vapour7 electrons in outer shell (-1 ion)Less reactive down the groupMore reactive Halogens displace lesser reactive halogens

http://www.youtube.com/watch?v=u2ogMUDBaf4

Displacement ReactionsIn a displacement reaction the more reactive element takes the place of the lesser reactive element.For example

Potassium Iodide + Chlorine Potassium Chloride + Iodine

This happens because CHLORINE is more reactive than IODINENoble GasesNoble gases are UNREACTIVE.They have a full outer shell of electrons.They have a very LOW DENSITYUses of HALOGENS:Helium balloonsNeon Bulbs and lampsArgon Welding to stop reactions with OXYGENExothermic and EndothermicExothermic reactions give out heat energy (feel hot)Endothermic reactions take in energy from the surroundings (feel cold)

Energy is created from making and breaking bonds.Energy is released from making bonds.Energy is used to break bonds.Rates of ReactionTemperatureHotter = fasterConcentrationHigh concentration (more particles) = fasterSurface AreaBig surface area (lots of small pieces) = fasterCatalystsAdding a catalyst speeds up the reaction but is never used up (used and then reformed)

Collision TheoryFor a reaction to occur then molecules must collide together with enough energy for the bonds to break.This causes a chemical reaction and new bonds will form between the atoms.

If the energy to break the bonds is more than that of the bonds made then the reaction is ENDOTHERMIC.If the energy to break the bonds is less than that to make the bonds then the reaction is EXOTHERMIC.

Relative Atomic Mass and Relative Molecular MassThe relative atomic mass of an atom is the same as the TOP number (mass number)E.g. Carbon = 12Oxygen = 16

The relative formula mass is the total mass of all atoms in the moleculeE.g.Carbon Dioxide (CO2)(1 x Carbon) + (2 x Oxygen)(12) + (2 x 16) = 44Empirical FormulaFrom the masses of reactants, it is possible to calculate anempirical formula. The empirical formula is the simplest ratio of atoms of each substance in the formula.

Theoretical Yield (what you should make)We can use masses in a reaction to help us calculate the amount of reactant and product.Step 1 - Write out the equation for the reaction. Make sure it is balanced.Step 2 - Work out the relative masses of the substances needed in the calculation. Remember to multiply by the number of molecules that are present.Step 3 - Convert the relative masses into the units in the question.Step 4 - Find the ratio by dividing both numbers by the smallest relative mass.Step 5 - Find the mass of the unknown by multiplying the mass of the known by the ratio of the unknown.Percentage YieldPercentage Yield = Actual Yield Theoretical Yield

The Actual Yield is how much you have made from the reaction (from the question).The Theoretical Yield is how much you should make if you have no loss what so ever (100% efficient).

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