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Element, compound and mixture

ELEMENT-a pure substance made up of one type of atom

COMPOUND-made up of two or more elements chemically combined together

MIXTURE-two or more elements or compounds are mixed together, not chemically combined

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Atomic and electronic structure

(http://physics.taskermilward.org.uk/KS4/additional/radioactivity/atomic_structure.gif)         Electron Rules

Particle    Relative Charge      Mass                 1st level holds maximum of 2 electrons

Electron            -1                very small               2nd and 3rd level hold 8 electrons

Proton              +1                      -1                    The 4th level holds 2 electrons                       Neutron             0                       -1

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Atomic structure 2

mass number/atomic mass-protons+neutrons in the atom 

atomic number/proton number-number of protons or electrons in the atom

 

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Structure of the atom developments

  • In 1905, Rutherford designed an experiment to test the plum pudding model. It was carried out by his assistants Geiger and Marsden. A beam of alpha particles was aimed at very thing gold foil. Instead of the particles passing straight through, they came out at different angles. The  plum puding model was replaced by the nuclear model of the atom
  • Niels Bohr developed the nuclear atom model 
  • In May 1932, James Chadwick discovered the neutron

Plum pudding model-sphere of positive charge with negatively charged electrons dotted around inside it

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Isotopes

Isotopes-atoms of the same element which have:

  • Same number of protons (and electrons)
  • Different number of neutrons

                                  3                                         4

                 He                    He

                           2                                 2

Protons               2                                 2

Neutrons             1                                 2  

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Atoms to ions

(http://chemactive.com/GCSE-Chemistry-Blog/wp-content/uploads/2013/05/ionic-bonding.png)

They lose/gain electrons to get a full outer shell

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Graphite

  • Layers of carbon atoms held together by intermolecular forces
  • Layers can slide over each other-softer then diamond
  • Used in pencils and as a lubricant
  • Each carbon atom is joined to 3 others, forming rings of 6 atoms, creating a giant structure 
  • Conducts electricity-free delocalised electrons
  • Has a very high melting point-strong covalent bonds between the atoms
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Diamond

  • Each carbon atom is joined to 4 others
  • Giant covalent structure (tetrahedral arrangement)
  • Very hard
  • High melting point-strong covalent bonds
  • Doesn't conduct electricity-no free electrons
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Nanoparticles

A nanoparticle is a very small particle

Nano-science is the study of particles that are 1-100nm in size

  • Nano-science is used in cars, silk, spacecraft, face cream, waterproof clothing, future technology, toothpaste and make up
  • They produce new properties (can be manipulated), have a large surface area for a small volume 

Potential Risks:

  • Spread easily through air and water
  • Can enter the body through the lungs or skin
  • May have unwanted effects on people and the environment
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The Periodic Table

  • Vertical columns-groups.amount of electrons on the outer shell
  • Period numbers-how many shells there are
  • Elements with similar properties are arranged in groups

Newlands-1864

  • Law of octaves-found that each element was similar to the elemetns eight places ahead
  • He put iron in the same group as oxygen and sulphur

Mendeleev-1869

  • He arraned the known elements in order of relative atomic mass
  • He arranged elements with similar properties into groups
  • Some elements were undiscovered, so he left gaps

Moseley-1913

  • Discovered atomic numbers
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Group 1 metals

Group 1 metal           Observation when reacting with water

Lithium                      Moving, hydrogen gas, fizzing, dissolved

Sodium                     Formed a ball, fizzing, moving, hydrogen gas

Potassium                 Burst into lilac flames, spitting, moving, fizzing, dissolving, hydrogen gas

Rubidium                  Hydrogen gas, spitting, fizzing, moving, dissloved, exploding

Caesium                   Explodes, spitting, hydrogen gas, biggest reaction

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  • Group 1 metals are very reactive
  • Group 1 increases in reactivity as the outer electron gets further away from the nucleus
  • We can make them more stable by reacting them with other chemicals
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Ionic bonding

(http://www.sciencerifi.co.uk/Content%20pages/Chemistry/Ionic%20bond.png)

  • Ionic bonding is when a metal reacts with a non-metal
  • Metals lose electrons-become positive
  • Non-metals gain electrons-become negative
  • The connection between them is ionic-ionic bonding
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Covalent bonding

Covalent bonding is between non-metals (on the right hand side of the periodic table)

They share a pair of electrons so they have a full outer shell

                          (http://www.bbc.co.uk/staticarchive/559ecdf85308c2ed04900fae1409198fad23b519.gif)

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Ionic compounds

Properties

  • High melting points-the ions are strongly bonded together (high temperature needed to spe, each ion is surrounded by oppositely charged ions held in place by electrostatic attraction and froming an ionic crystal lattice
  • Conduct electricity when aqueous (dissolved in water) or molten-when melted or dissolved in water, the ion is free to move and the substance can conduct electricity
  • Don't conduct electricity when solid
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Small molecules (covalent structures)

Properties

  • Low density
  • Low melting and boiling points
  • Don't dissolve in water
  • Don't conduct electricity-no free electrons
  • Bonds binding the atoms together are very strong
  • Weak intermolecular forces hold the molecules together
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Flame Tests

Calcium-red

Sodium-yellow

Potassium-lilac

Lithium-crimson

Copper-green

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Metal hydroxides

Metal (salt) 1cm      Addition of hydroxide (1cm)          Addition of excess hydroxide (2cm)

Aluminium               White precipitate                            Re-dissolves in excess hydroxide

(sulphate)                 

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Calcium                  White precipitate                             No change

(nitrate)

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Magnesium             White precipitate                             No change

(chloride)

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Metal hydroxides 2

Metal (salt)                  Addition of hydroxide

Copper (II) chloride     Blue precipitate

Iron (II) chloride           Green precipitate

Iron (III) chloride          Brown precipitate

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Testing for sulphates

1) Add 1cm of magnesium sulphate to your test tube

2) Add 1cm of hydrochloric acid

3) Add 1cm of barium chloride and shake 

Our result was a white precipitate-sulphate ions

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Testing for halides

1) Add 1cm of the metal halide compounds to the test tube

2) Add 1cm of nitric acid

3) Add 1cm of silver nitrate solution 

4) Place a bung in the top and gently shake

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           Halide Ion       Observations

           Chloride           White precipitate

           Bromide           Cream precipitate

           Iodide              Yellow precipitate  

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Testing gases

  • Carbon dioxide-a lighted wooden splint goes out
  • Hydrogen (squeaky pop test)-a lighted wooden splint makes a popping sound
  • Oxygen-a glowing wooden splint relights
  • Chlorine-damp blue litmus paper turns red, then bleaches it white
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Testing for carbon dioxide

         (http://www.edplace.com/userfiles/image/ReactionsofAcids-MetalCarbonates.jpg)

Limewater turns cloudy-carbon dioxide is present

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Crude oil

Crude oil is a mixture of compounds called hydrocarbons, that only contain the elements carbon and hydrogen.

  • Sea animals die and their remains sink to the sea floor
  • Remains are covered by layer upon layer of sediment
  • Over time pressure increases and remains begin to decay
  • Decaying remains slowly turn into oil
  • Oil reserves found and pumped to surface
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Alkanes

Formula-CnH2n+2

Saturated

C-C bonds

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Alkenes

Formula-   CnH2n

Unsaturated

1 C=C bond

Turn colourless when mixed with bromine water

Substitution-halogen + alkene

Hydrogenation-hydrogen + alkene

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Alcohol

Formula- CnH2n+1OH

Have differetn boiling points because of the amound of carbons

Uses:

  • Mouthwash       Burning
  • Solvent             Sterilise
  • Perfume           Drinking
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Carboxylic acids

(http://www.nomenclature101.com/en/img/nom/nom72.png)-written as COOH             CnH2n+1OOH

Properties-high melting and boiling points, very soluble in water, weak acids, have a characteristic smell

Citric acid-citric fruits | Lactic acid-tired musces | Malic acid-sour and tart foods

Oxygen is present

                           Ethanol + oxygen ---> ethanoic acid + water

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Esters

Carboxylic acid + alcohol  ---> ester + water

Immiscible (don't mix) with water, so they float on the surface-less dense than water

End in oate-methyl propanoate

Propyl ethanoate-smells of pears

Butyl butanoate-smells of pineapples

Methyl butanoate-smells of apple

 

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Cracking

The shorter the carbon chain (crude oil) the greater the demand

In cracking, long chain alkanes are heated and broken up into smaller, more useful molecules

This is an example of thermal decomposition (breaking something down using heat)

Catalyst-substance that speeds up a chemical reaction, lowers the activation energy and doesn't get used up

The product of crackng is ethene or propene

Methene doesn't exist because it only has one carbon (http://pythagorasandthat.co.uk/wp-content/uploads/2014/07/hexane-cracking.gif)

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Cracking

The shorter the carbon chain (crude oil) the greater the demand

In cracking, long chain alkanes are heated and broken up into smaller, more useful molecules

This is an example of thermal decomposition (breaking something down using heat)

Catalyst-substance that speeds up a chemical reaction, lowers the activation energy and doesn't get used up

The product of crackng is ethene or propene

Methene doesn't exist because it only has one carbon (http://pythagorasandthat.co.uk/wp-content/uploads/2014/07/hexane-cracking.gif)

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Combustion

Combustion-burning

Complete combustion-burning with lots of oxygen

Incomplete combustion-burning with a limited oxygen supply

3 things needed for combustion:

  • Fuel
  • Heat 
  • Oxygen

Combustion is an oxidation reaction-addition of oxygen

Complete-water and carbon dioxide produced

Incomplete-carbon monoxide, water, carbon (soot) are produced

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Fractional distillation

Fractional distillation is used to separate mixtures of liquids 

The more carbon atoms in a hydrocarbon, the higher the boiling point

Fractions that have a low boiling point evaporate easily. The easier a fraction evaporates, the more volatile it is.

The shorter the carbon chain/fraction, the more volatile and flammable it is

The longer the hydrocarbon chains in a fraction, the more viscous (thick) the fraction will be

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Polymers

Ethene is a monomer (one part)

Polythene is a polymer-small molecules oin end to end to form a large polymer chain

(http://www.chemhume.co.uk/ASCHEM/Unit%202/Ch9%20Alkanes/poly(ethene).jpg)

Thermosoftening polymers have weak forces between the chains so they can slide past each other

Thermosetting have strong intermolecular forces so are held in place

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Disposal of polymers

                                      Advantage                                              Disadvantage

Landfill          |  Doesn't give off toxic gas                  |  Shortage of suitable places

                      |  Covenient                                       |  Destorys habitats

                      |                                                       |  Stays for hundreds of year

Incineration   |  Releases lots of energy which can     |  Can give off toxic gases

                      |  be used to generate electricity          |

                      |                                                       |

Recycling       |  Re-used for other things                  |  Must be collected and sorted-costs

                      |  Saves natural resources                   |

                      |                                                       |

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