- 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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- 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.
- 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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- 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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