Chemistry

AQA

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  • Created by: lrmm
  • Created on: 25-05-10 21:28

Structures and Bonding

  • Atoms are made of protons, neutrons and electrons.
  • Prtons and electrons have equal and opposite charges. Protons + and electorons -
  • The electrons in an atom are arranged in energy leevels or shells.
  • Atoms with sam number of electronsin outer shell belong in same group.
  • Number of electrons in outer shell dtermines how the atom behaves.
  • Elements react to form compounds by gaining or losing electrons or by sharing electrons.
  • Group 1 react with group 7.
  • Ionic compunds are held together by strong forces between oppositely charged ions.
  • Covalent bonds formed when atoms share elecyrons.
  • Many substances ocontaining covalent bonds consist of molecules, but some have giant covalent substances.
  • Atoms in metals arranged in regualr layers.
  • Positive ions in metals are held together by electrons forom outer shell of each metal atom. These electrons are delcoalised. and are free to move throughout metal lattice.
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Stucutres and Properties

  • Takes a lot of energy to break bons which held together a giant ionic structure. Ionic compounds have high mp and bp.
  • Iionic compounds will conduct electricity when molten or dissolved as their ions can move freely.
  • Substances made up of simple molecules have low mp and bp and forces between simple molecular are small and intermolecular forces are weak and overcome.
  • Simple molecules have no overall charge so cannot conduct electrivity.
  • Some covalent bonded substances contain giant structures which have high mp.
  • Giant strucutre of graphite contains layers which slide over each other so is slippery. Diamond has different strucutre so is hard.
  • Graphite conducts electricity because of the delcolaised electrons alons its layers
  • We can bend and shape metals because layers of atoms in a metal can slide over each other.
  • Delocalised electrons in metals allow them to conduct heat and electricity.
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Mass Numbers

  • Relative mass of protons and neutrons is 1
  • Mass number of atom tells total number of protons and neutrons.
  • Isotopes are atoms of same elememtn with different number of neutrons.
  • Mole=Mass/Mr
  • Yield of chemical tells us how much product is made.
  • % yield of chemical reaction tellus us how much product is made compared with maximum amount.
  • Factors effecting yield: producr may been left behind in apparatus.
  • Maximise atom enconomy to conserve resources and reduce pollution.
  • Reversilbe reaction, products can react to make origional reactants.
  • In a closed system the rate of forward and backward are equal at equilibrium.
  • Changing the reaction conditions can change the amounts of products and reactants in a mixture.
  • Ammonia is an important chemical for making other chemicals, including fertilisers.
  • Ammmonia is made from Haber process.
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Rates of Reaction

  • Measure rate of reaction by following rate at which reactants used up of products formed.
  • Minimum amount of energy that particles must have in order to react is called activation energy.
  • Rate at which chemical reaction increases if the surface area of a solid is increased.
  • Happen more quickly at higher temperatures as patricles collide more so more energy.
  • Increasing concentration increases frequncy of collision between particles increasied rate.
  • Increasing pressure results in particles colliding more often/
  • Catalyst speeds up rate of reactions
  • Not sued up during reaction.
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Energy and Reactions

  • Energy may be transferred to of from reacting substances in reaction.
  • Energy transferred to surroundings- EXOTHERMIC
  • Energy transferred to reacting substances- ENDOTHERMIC
  • In any reversible reaction, amount of energy released when reaction goes in one direction is equal to energy absorbed in opposite direction.
  • Change amount of product formed by changing temp.
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Electrolysis

  • Involves splitting up a sunbstance using electricity.
  • Ionic substances can be electrolylised when molten or in solutions.
  • Positive ions move to CATHODE. Negative ions move to ANODE.
  • Negative ions are oxidised while positive are reduced.
  • Electrolysis in water-less reactive element produced at electrode.
  • Electrolyse brine, we get chloring, hyrdrogen and soduim hyrdroxide.
  • Chlroing kills microbes in pools and hydrochloric acid. Hydrogen used to made margarine. Sodium hydroxied- bleach, paper and soap.
  • Copper extracted from its ore contains impurites such as gold and silver.
  • Copper purified by electrolysis to remove impurities.
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Acids, alkalis and salts

  • Acids are substances which produce hydrogen ions when added to water.
  • Bases neutralise acds-metal oxide/hyrdoroxide.
  • Alkalis is a soluble base. Produce hyrdorixde ions when added to water.
  • Acid+base=neutralisation=salt and water
  • Salts made by reacting metal with acid and produces hyrrogen.
  • Insoluble salts made by reacting two solutions to produce precipitate.
  • Precipitation is an important way of removing some substances from wastewater.
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