Chemistry Revision

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Atoms

The Nucleus                                                            

  • In the middle of an atom                         Neutral atoms have no charge overall                   
  • Contains protons and neutrons               Charge on electrons is oppostie charge to protons
  • Positive charge                                           Number of electrons equals number of protons

The Electrons                                                 Molecules are groups of atoms

  • Move around the nucleus                         Atoms can join together to create molecules
  • Negatively charged                                 Molecules can be made up by one or more elements
  • No mass                                                 Held together by covalent bonds
  • Tiny, but cover a lot of space

 

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Halogens - Group 7

Chlorine      17    green           gas   The properties change as you go down the group

Bromine      36    red-brown    liquid     

Iodine         53    dark grey      solid

The higher up the element is, the more reactive it will be as the shell with the missing electron is nearer to the nucleus, so the pull from the positive nucleus is greater.

You can use these trends to predict the properties of other haolgens e.g. fluorine

The elements in Group 7 take place in displacement reactions. This is where a more reactive element "pushes out" a less reactive element from a compound.

Chlorine & Iodine - Chlorine is more reactive. If you add chlorine water to potassium iodide solution they will react and create potassium chloride.

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Reactivity Series

Potassium       K

Sodium       Na

Lithium       Li

Calcium       Ca

Magnesium       Mg

Aluminium       Al

Zinc       Zn

Iron       Fe

Copper       Cu

Silver       Ag

Gold       Au

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Iron

Iron corrodes easily. It rusts.

Rusting only happens when the iron is in contact with oxygen and water.

The chemical reaction that takes place is oxidation. The iron gains oxygen to form iron(III) oxide.

Water becomes loosely bonded to the Iron(III) oxide and the result is hydrated iron(III) oxide.

iron + oxygen + water -----> hydrated iron(III) oxide (rust)

To prevent rusting you can coat the iron with a barrier :

Painting/Coating with plastic - ideal for big and small structures.

Oiling/Greasing - has to be used when moving parts are involved, such as bike chains.

Zinc is often used as a sacrificial metal due to Zinc being more reactive than Iron.

A coating of Zinc can be sprayed onto the object, this is known as galvanising.

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