the modern periodic table

Question 1

in the early 1800s how was the elements arranged

Answer 1

by their atomic weight

Question 2

early 1800s

Answer 2

these early periodic tables were not complete this is because not all of the elements have been found
and therefore putting the elements in order of atomic weight meant that some elements were also put in the wrong group

Question 3

DIMITRI MENDELEEV LEFT GAPS AND PREDICTED NEW ELEMENTS

Answer 3

in 1869 scientist mendeleev took all of known elements and arranged them in the table
he ordered them mainly in atomic weight
however sometimes switched positions and left gaps
this was so that he could make sure that elements with similar properties stayed in same group
some left gaps and left space for elements that hadnt been found yet
mendeleev used the position of gaps to PREDICT the properties
new elements have been found since which fit into these gaps this proves that mendeleev idea was right

Question 4

isotops

Answer 4

isotops were discovered a little while back after mendeleev made his table of elements
isotops have different masses but share same properties meaning they have same position in periodic table
so this shows that mendeleev was right to swap some elements around to keep properties together EVEN if they were not n order of atomic weight