The Periodic Table - History

Question 1

What happened in the early 1800’s?

Answer 1

• Elements were categorised by their physical & chemical properties as well as their relative atomic mass.
• Protons and electrons were not yet discovered.

Question 2

What happened in 1817?

Answer 2

• Johann Döbereiner grouped similar elements in groups called Döbereiner’s triads (groups of 3).
• Noticed that Cl, Br & had similar characteristics.

Question 3

What happened in 1863?

Answer 3

John Newlands made first Periodic table of elements.

He noticed that by arranging elements in order of mass, similar trends appeared at regular intervals and every eighth element was similar (named law of octaves) so arranged them in rows of seven (to make them line up).

Question 4

What happened in 1869?

Answer 4

Dimitri Mendeleev created the first accepted version.

He arranged elements by atomic mass, leaving gaps where elements didn’t fit, so the groups of similar properties could be retained.

Also correctly predicted properties of undiscovered elements.

Question 5

What happened in 1914?

Answer 5

Henry Mosely produced the modern periodic table.

Arranged by increasing atomic number NOT mass.