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  • Created by: jacktd98
  • Created on: 09-05-15 17:41

Atoms

  • Atoms are made up of of subatomic particles. these are protons nuetrons and electrons.
  • the mass number is the larger number and is the total number of protons and neutrons
  • the atomic number is smaller and represents the number of protons alone
  • a compound is formed when two different element chemically combine

Isotopes

  • isotopes are different forms of the same element, they have the same number of protons but a different number of neutrons
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Ionic bonding

Atoms lose or gain electrons to form charged particles called ions which are then attracted to each other 

  • the ions are held together by the electrostatic force of attraction which acts equally in all directions
  • Group 1 and 2 elements (metals) bond ionically with group 7 and 6 elements (non-metals)
  • Group 1 - alkali metals     Group 7 - halogens 

Ionic structures 

  • the ions form in giant ionic lattices
  • the ions for a regular lattice arrangement

Properties 

  • they have high boiling and melting points due the the strong attraction between the ions, it takes a large amount of eneergy to seperate the ions
  • when in liquid form the ions can carry an electric current
  • they dissolve easily in water and the ions seperate and once again carry current 
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Covalent Bonding

Covalent bonding involves atoms sharing electrons to form molecules (usually non meals)

Simple molecules 

  • the covalent bonds (the shared electrons) between the atoms are very strong
  • the intermolecular forces between the atoms are very weak
  • this means very low melting and boiling points
  • most molecular gasses or liquids at room temperature
  • they do not conduct electricity

Giant covalent structures - macromolecules

  • similar to ionic structures but there are no charged ions
  • all the atoms are bonded together by strong covalent bonds
  • they are very hard, have high melting points and boiling points and are insoluble in water 

diamond, silicon dioxide (silica, sand)  graphite - layers of hexagons slide over each other, contains delocalised electrons which conduct electricity along the layers 

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Metallic structures

  • consist of a giant structure
  • contaion delocalised electrons from the outer shell of every metal atom
  • these electrons hold the atoms together in a regular structure - electrostatic attraction between electrons and positve ions
  • they also carry electricity well and heat
  • form in layers which slide over each other allowing metals to be bent and shaped
  • alloys contain other atoms which distort the layer making them harder 

smart alloys

  • made from nintol (nickel and titanium)
  • bend it then heat and it returns to 'remembered shape
  • e.g. glasses, braces
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Nanoparticles

  • 1-100 nanometres across 
  • have a huge surface area to volume ratio
  • used as: stronger and lighter building material, sun tan cream and deodrant, lubricant coatings

fullerenes

  • molecules of carbon shaped like hollow balls or closed tubes
  • Each carbon atom forms 3 covalent bonds, with its neighbours, leaving free electrons that can conduct electricity
  • carbon atoms aranged in hexagonal rings 
  • they are very strong
  • could be used in the future to carry drugs to places in the body
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Polymers

we make polymers from chemicals made from crude oil. Small molecules called monomers join together through polymeriasation. the properties of the polymer depend on:

the monomers used to make it                 the conditions we choose to carry out the reaction

Polyethene

low density - 200 C very high pressure - flexible, branched chains - bags and bottles

high density - lower temp 50 C, lower pressure (catalyst) - more rigid more closely packed - water tanks drainpipes

thermosoftening - thermosetting

 thermosoftening - individual tangled chains with no crosslinks, weak intermolecular forces - melt easily and set in different shape easily remoulded.

thermosetting - covalent bonds betwee links (crosslinks) - solid structure do not melt but burn, strong hard and rigid 

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Analysing substances

paper chromatography

  • compunds dotted along a pencil line, some of these compounds are more soluble (dissolve easily) than others in the solvent and this determines how far up the paper they travel
  • we then compare the results with those of known substances - same variables must be kept e.g temp, same solvent

Gas chromatography 

  • sample mixture injected and vapourised
  • carrier gas moves the vapour through the coiled column
  • the compounds have a different attraction to the material in the column - the stronger the atrraction the longer the retention time
  • retention times recorded then compared to known substances
  • a mass spectrometer can be used to messure the relative formula mass of the compound 
  • look the molecular ion peak or the last peak on the right to find RFM

Advantage/disadvantages - more accurate/faser/ smaller samples able to be analysed - very expensive/need special training/has to be compared with known data

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Rate of reaction

•the temperature is increased

•the concentration of a dissolved reactant is increased

•the pressure of a reacting gas is increased

larger surface area - solid reactants are broken into smaller pieces 

•a catalyst is used

colision theory

Chemical reactions can only occur when reacting particles collide with each other and with sufficient energy. The minimum amount of energy particles must have to react is called the activation energy. 

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Energy transfer in reactions

Exothermic - transfers energy to surroundings - noted by rise in temp - burning fuels, oxidation reactions(respiration), neutralisation - self heating cans, hand warmers  

Endothermic - takes energy in from surroundings - noted by drop in temp - thermal decomposition -  Some sports injury packs are based upon endothermic reactions. 

in reversable reactions the reaction is exothermic in one direction and endothermic in the other, the energy absorbed is equal to the energy given out in either direction

hydrated     endothermic      anhydrous

copper       ------------------->      copper     + water

sulfate       <------------------       sulfate

(blue)         exothermic         (white)

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Making salts

Acid + metal ----> salt +hydrogen

  • metal must be more reactive than hydrogen 
  • Hydrochloric acid + Magnesium -------> Magnesium chloride + hydrogen
  • 2HCl(aq) + Mg(s) ------>  MgCl2(aq) + H2(g)

Acid + Metal Oxides/Hydroxides ------> Salt + Water 

  • Hydrochloric acid + Copper oxide ----> copper Chloride + water

How to make

SOLUBLE SALTS <------ ACID + METAL or INSOUBLE BASE(alkili that doesnt dissolve)

  • add the metal, metal oxide or metal hydroxide to the acid (neutralisation)
  • solid will start to dissolve, finished when excess sinks to bottom
  • filter out the excess 
  • if oxide/hydroxide evaporate water
  • then leave the rest to evaporate slowly (crystallisation)
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Making salts cont.

SOLUBLE SALTS <-------- ACID + ALKALI(a base that dissolves - is soluble)

  • neutralisation reaction using an indicator to find reaction endpoint 
  • repeat without indicator so not contaminated
  • evaporate off water to crystallise the salt

INSOLUBLE SALTS <------- 2 SALT SOLUTIONS - Precipitation reaction

  • each reactant should contain one of the ions of the insoluble salt 
  • mix the two together
  • salt forms and sinks to bottom of flask - precipitant
  • wash it then dry on the filter paper

Hydrogen ions, H+(aq), make solutions acidic and hydroxide ions, OH–(aq), make solutions alkaline.The pH scale is a measure of the acidity or alkalinity of a solution. In neutralisation reactions, hydrogen ions react with hydroxide ions to produce water. This reaction can be represented by the equation: H+(aq) + OH–(aq) H2O(l)

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Ammonia

  • Amonia dissolves in water to make an alkaline solution
  •  when it reacts with Nitric acid it forms a neutral salt - ammonium nitrate

NH3(aq) + HNO3(aq)  ------> NH4NO3(aq)

Ammonia + Nitric Acid --------> Ammonium nitrate 

NO WATER PRODUCED

ammonium nitrate is a very good fertilizer, it has two sources of nitrogen - plants need nitrogen to make proteins 

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Electrolysis

When an ionic substance is melted or dissolved in water, the ions are free to move about within the liquid or solution. Passing an electric current through ionic substances that are molten, for example lead bromide, or in solution breaks them down into elements. This process is called electrolysis and the substance that is broken down is called the electrolyte. During electrolysis, positively charged ions move to the negative electrode, and negatively charged ions move to the positive electrode.

OIL RIG - electrolysis always involves reduction and oxidation

Oxidation                      Reduction

Is                                 Is

Loss (of electrons)         Gain (of electrons)

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Electrolysis of solutions

many ionic substances have very high melting points but dissolve in water. when this happens the ions become free to move. when electrolysing these solutions the water also breaks down into ions - H+ and OH- ions.

if the metal ions going to the negative electrode are more reactive than the H+ ions they will remain in the solution and the hydrogen will reduce.

if there are halide ions (group 7) present as well as OH- ion at the positive electrode, the halides will will form. if no halide than oxygen will be formed.

HALF EQUATIONS

half equations show the reactions at the  electrodes

Negative electrode: 2H+    +    2e- ------>   H2

Positive electrode:  2CL  ------> Cl2   +   2e-

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Sodium Chloride solution (BRINE)

The electrolysis of sodium chloride solution produces hydrogen and chlorine. Sodium hydroxide solution is also produced.

At the negative electrode: two hydrogen ions (H+) accept two electrons to form a hydrogen gas molecule (H2)

At the positive elctrode: two chloride ions (Cl-) lose their electrons to become one Chlorine gas molecule (Cl2) 

The sodium ios stay in the solution and the hydroxide ions are left behind this forms sodium hydroxide solution.

These are important reagents for the chemical industry,

  • sodium hydroxide - for the production of soap and paper 
  • chlorine - reacted with the sodium hydroxide producing bleach and also used in plastics
  • hydrogen - reacted with vegtable oils to form margarine
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Extraction of Aluminium

Aluminium is more reactive than Carbon so must be extracted from its ore through electrolysis. The ore that is most commonly used for the extraction is Bauxite. it is mined by open cast mining and is a mixture of Aluminium oxide (AL2O3) and iron(III) oxide (rust) giving it the browny orange colour. the aluminium oxide is seperated from the bauxite giving us the pure aluminium oxide in a white powder form.

To perform electrolysis the aluminium oxide must be liquid but its melting point is 2050*C. To save energy and money the Aluminium oxide is dissolved into molten cryolite (another ionic compound). This can then be electrolysed at 850*C.

  • Carbon electrodes used (graphite)
  • positive electrode rods put into solution
  • cell has a graphite lining acting as negative electrode

At the negative electrode: The aluminium ion gains 3 electrons to form Al atoms which are molten and collect at the bottom of the cell to be tapped off

At the positive electrode: The oxide ion loses 2 electrons turning into oxygen atoms which bond in pairs, these then react with the carbon electrode to form CO2 which is then released burning away the electrode. This is done to stop oxygen being released causing massive combustion and an explosion 

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Electroplating

used to:

  • protect the object from corroding
  • make the object more attractive
  • increase the hardness and resistance to scratching
  • save money - gold plated 

the metal object to be plated is used as the negative electrode. the positive electrode is made of the the metal you want to use to plate the object. the electrolyte is made up of ions of the plating metal. these ions cover the object (negative electrode) and the positive electrode keeps the electrolyte 'topped up' and will need to be replaced.  

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