development of periodic table and the modern periodic table

before mendeleevs table the periodic table was sorted in order of increasing relative atomic mass

early periodic tables were not complete

the elements were placed in the wrong group with elements with different properties

mendeleev overcame these problems by arranging the elements in order of atomic mass but changed the order if the properties of the elements meant it should be switched

he also left gaps so that the elements were arranged in groups with similar properties allowing space for undiscovered elements

evidence that supported his periodic table…