1. The History of the Periodic Table

2. John Dalton (1808)
Ordered 36 elements
Gave each element a symbol

3. J.W. Dobereiner (1829) Looked at the recently discovered Bromine
and observed properties half way between chlorine and iodine.
Called the three elements a triad

5. Dmitri Mendeleev (1869 – 1871)
Listed the known elements in groups based on a set of repeating properties
He ordered them by atomic mass
Mendeleev's table worked...he left gaps in his the table if he thought an element had not been discovered.

7. Lothar Meyer (1869)
Published a table very much like Mendeleev’s table

8. Henry Moseley (1913)
Determined atomic number for each element known at that time

9. Periodic Law
When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.