Chemistry Unit 1

History of the Periodic Table

Early 1800s

• Two ways to categorise the elements

           1) Physical and chemical properties     2) Relative atomic mass

•  No such thing as atomic number until 20th century after protons and electrons were discovered.
• Known elements were arranged in the order of atomic mass, a periodc pattern was noticed in the properties of the elements.

Newlands' Law of Octaves

• Newland was the first person to arrange the elements usefully in 1864.
• Every 8th element had similar properties, so he listed the known elements in rows of 7
• These sets of eight were called Newlands' Octaves.
• His work was ignored because...

          1) His groups contained elements thatt didn't have similar properties.            

          2) He mixed up metals and non-metals e.g oxygen and iron

          3) He didn't leave gaps for elements yet to be discovered.  

Dmitri Mendeleev

• In 1869, Dmitri arranged 50 known elements into his Table of Elements…