History of the Periodic Table

-NO idea of: atomic structure, protons, electrons

-NO such thing as atomic number

They could measure relative atomic mass so known elements were arranged in order of atomic mass.

When this was done a periodic pattern was noticed in the properties of the elements.

This is where the name 'periodic table' comes from.

Elements were catergorised into: Physical and chemical properties

                                                     Relative Atomic Mass

A man called Newlands in 1864 noticed that every eighth element had similar properties so he listed elements in rows of seven.

These sets of eight were called Newlands' Octaves but unfortunately the pattern broke down on the third row due to transitional metals.

His work was criticised becuase:

1) His groups contained elements that did not have similar properties e.g. Carbon and titanium

2) He mixed up metals and non-metals e.g. O and Fe

3) He did not leave gaps for undiscovered elements so his work was ignored.

Dmitri Mendeleev in 1869 arranged his Table of Elements with various gaps

Put the elements in order of atomic mass but he left gaps to keep elements elements with similar properties in the same vertical coloums ( groups) and he left big gaps

The gaps predicted the properties of so far undiscovered element. When they were found they fitted the pattern.