Describe the development of the periodic table.

1)1800s - order of relative atomic mass - properties not taken into account 2)1869 - Dimitri Mendeleev - mainly atomic mass - (1)some switched for similar properties e.g. iodine has higher mass than Tellurium but placed after due to properties - (2)Gaps left to make sure similar undiscovered elements had room, when found they fitted pattern e.g. predicted ekasilicon known as Germanium. 3)Modern table - ordered in increasing atomic number giving repeating patterns - similar properties form columns