Development Of The Periodic Table

Question 1

What did scientists order elements by before the discovery of protons, neutrons and electrons

Answer 1

Arranging them in order of their atomic weight

Question 2

Why were some elements placed in the wrong group in the early periodic table

Answer 2

Because elements were placed in the order of relative atomic mass and did not take into account their properties

Question 3

What did Mendeleev do to overcome the problem

Answer 3

He left gaps for elements that he thought had not been discovered and in some places changed the order if the properties meant it should be changed

Question 4

Why did Mendeleev leave gaps

Answer 4

To indicate the existence of undiscovered elements and allow Mendeleev to predict what their properties might be

Question 5

Based on what knowledge made it possible to explain why the order based on atomic weights was not always correct

Answer 5

Discovery of isotopes confirmed Mendeleev was correct to not place elements in a strict order of atomic mass but to also take account of the properties