what differences exist in the arrangement of John Newland and Mendeleev?

Answer 1

Newland arranged his elements in "octaves" or 8s. he didn't know about the group called Inert Gases, so his table was one group short. His theory of properties being repeated every 8th element started to break down at the Transition Metals. Mendeleev had the sense to realise that there were unknown elements still to be found, and left room for them. He also realised that certain elements (eg Ar and K) appeared in the wrong places if put in strict atomic weight order, so he reversed them.