Chemistry- Periodic Table

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History of the periodic table

In the 1880's elements were arranged by either:

  • Their physical and chemical properties
  • Their relative atomic mass

This was because:

  • They had no idea of atomic structure or of protons and electrons. This meant they had no idea about atomic number.
  • The only thing they could measure was relative atomic mass and so the known elements were arranged in order of atomic mass. When this was done, a periodic pattern was noticed in the properties of the element and this is why it is called the periodic table.
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Newland and Mendeleev


Newlands noticed that every eighth element has similar properties so he listed some of the known elements in rows of seven. These sets of eight were called Newlands octaves but unfortunately the pattern broke down after the third row with transition metals messing it up. It was because he left no gaps why his ideas were ignored. Newlands ideas were ignored because:

  • His groups contained elements that didn't have somilar properties
  • He mixed up metals and non-metals
  • He didn't leave any gaps for undiscover elements 


In 1869, a russian scientist called Dmitri Mendeleev, arranged about 50 elements as shown in the picture. like Newlands he arranged elements in order of atomic mass but crucially mendeleev left gaps for undiscoverd elements. Also he found he had to leave gaps to keep elements with similar properties together. 

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Modern Periodic Table

How scientists opinions changed:

  • There was no real evidence to that it worked for all elements
  • After Mendeleev released his work newly discovered elements fiited into his gaps which started to covince some people
  • Once there was more evidence people started to belive it worked therefore thought it was more useful
  • In the late 19th century protons, neutrons and electrons were discovered and these all matched with the periodic table therefore giving more evidence

When electrons, neutrons and electrons were discovered the table was arranged by periodic number

  • Using electron arrangement you can predict the element's chemical properties
  • Electrons are set out in shells which correspond to energy levels
  • Elements in the smae group have the same number of elctrons in their outer shell
  • group number is equal to the amount of electrons on the outer shell
  • Further from the nucleus the less the attraction
  • Electron in outer shell is most easily lost because there is less attraction
  • higher energy level unlikely to gain an electron becuase of less attraction from the nucleus pulling electrons into the atom
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