The Periodic Table - AQA C3.1

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The early periodic table


  • Ordered elements by atomic weight
  • Used law of octaves (similarities in every 8th element)
  • This law didn't work because lots of grouped elements were not similar, for example metals and non metals in the same group
  • Only worked for first few elements
  • Didn't account for any new elements


  • Ordered elements by atomic weight
  • Left gaps for undiscovered elements so groups did have the same properties
  • Predicted masses and properties of missing elements
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The modern periodic table

Elements are ordered by atomic number.

The number of electrons in the outer shell of an atom is equal to its group number.

Elements with the same number of electrons in their outer shells have similar chemical properties.


  • The bigger the distance between outer electrons and nucleus, the weaker the force of attraction and the more likely the electrons are to be lost
  • Metals loose an electron when they react, so reactivity increases down the group
  • Non metals gain an electron when they react, so reactivity decreases down the group
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Group 1 - Alkali metals

  • Low density
  • React with non-metals to form ionic compounds
  • React with water to produce hydrogen
  • Produce hydroxides that dissolve in water to give alkaline solutions

The further down the group, the more reactive and lower the melting and boiling point is.

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Group 7 - Halogens

  • Poor conductors
  • Poisonous
  • Produce coloured vapours: Flourine, Chlorine, Bromine, Iodine
  • React with metals to form ionic compounds
  • Ion produced is called a halide with a charge of -1

The further down the group you go, the less reactive and higher the melting and boiling points

A more reactive halogen can displace a less reactive one from an aqueous solution of its salt.

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Transition metals

  • Found between groups 2 and 3

Compared to group 1:

  • Higher melting and boiling points
  • Much harder and stronger
  • Much less reactive (won't react with oxygen or water)
  • Form ions with different charges
  • Form coloured compounds
  • Useful as cataylsts
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