Developments in the Periodic Table

Events

Johann Döbereiner

1817

This German scientist put forward his law of triads. In each of the triads the element had similar appearances and chemical reactions. He discovered that the relative atomic mass of the middle element in each triad was roughly the average of the other 2 atomic masses. This helped other scientists figure out that atomic masses were important when arranging the elements.

John Newlands

1864

This English chemist ordered all the elements in atomic weight and noticed that every 8 elements had similar chemical and physical properties. He called this model the ‘law of octaves’.

Dmitri Mendeleev

1869

This Russian chemist created a periodic table which also had the elements in order of atomic weight but also had the elements with similar properties underneath each other. He also left gaps for other elements to be discovered.

William Ramsey

1894

This Scottish chemist invented a new section of the periodic table that obtained noble gases.

Henry Moseley

1914

This English physicist discovered the atomic number for every element. When doing this he realised that by ordering the elements in atomic number rather than atomic weight the periodic table would fit together better.

Glenn Seaborg

1940

This American chemist created a new section of the periodic table called ‘actinides’. He made this new section when he artificially produced heavy mass elements (neptunium).