'The History of the periodic table'

Question 1

Wolfgang Döbereiner

Answer 1

In 1829, Johann Wolfgang Döbereiner found that there were groups of three elements which had similar properties. Relative atomic masses (r.a.m) were being measured at this time and he noticed a curious relationship. The average r.a.m. of the first and third elements was equal or close to the r.a.m. of the second element.

Question 2

John Newlands

Answer 2

John Newlands arranged the 60 elements known at the time into a table in order of relative atomic massHe suggested that starting from a given element every 8th element has similar properties. In the table, every 8th element starts a new row, so the columns contain elements with similar properties. He called this the “Law of Octaves”.

Question 3

Dmitri Mendeleev

Answer 3

In 1869 Dmitri Mendeleev published a periodic table. Like Newlands, he arranged the known elements in order of relative atomic mass but the key difference was that he left gaps so that elements with similar physical and chemical properties were in the same vertical groups

Question 4

Mosley

Answer 4

Since Mendeleev’s time, elements in the periodic table had been arranged according to their relative atomic masses. However, the position predicted by an element’s relative atomic mass did not always match the position predicted by its chemical properties.

Question 5

current time

Answer 5

In the last 100 years new elements have been discovered to give the complete table shown.

Elements after uranium do not occur naturally and are made by bombarding other elements with high energy particles. These elements are radioactive.