development of the periodic table chemistry aqa gcse

how are the elements arranged?

in order of increasing atomic number

how do you read the periodic table?

from left to right and top to bottom

what do we call each column?

a group

what were Mendeleev’s discoveries?

- he found that the elements displayed a pattern of chemical properties that repeated in regular intervals

- so he formed new rows each time the pattern repeated called periods

why do elements in the same group have similar chemical properties?

they have the same number of electrons in their outermost shell

How did Mendeleev organize his periodic table?

in order of increasing atomic mass however not all elements fit with the pattern so he changed their order where necessary, because he realised that elements with the same properties should be placed in the same columns

he also left gaps as he realised that not all the elements had been discovered yet

he used the properties and trends of other elements in the group with the gap to predict the properties of these undiscovered elements

what made it possible to explain why the order based on atomic mass was incorrect?

knowledge of isotopes

John Newlands ideas

- in 1864 he built on dalton's ideas

- he arranged the elements in order of mass but realised that the properties of every eighth element seemed similar

- so he produced a table showing his law of octaves

what was the flaw with Newlands' 'law of octaves'?

he assumed all the elements had been found and didn't take into account chemists were still finding new ones