In the early 1800s they could only use atomic mass
Categorisation through
Physical and chemical properties
Relative atomic mass
No idea of atomic structure or
protons/electrons
Nota:
No such thing as atomic number - only in C21st after protons and electrons were discovered that it was realised that elements were best arranged in order of atomic number
Could only measure relative
atomic mass - known elements
arranged in order of atomic mass
Newlands' law of Octaves was the first good effort
Had the first good method of arranging in 1964
Nota:
Noticed that every eighth element had similar properties, so listed some of the known elements in rows of sevens
The sets of eight were called Newlands' Octaves
Nota:
Unfortunately the pattern broke down on the third row - transition metals (Titanium Ti and Iron Fe) messed it up.
He left no gaps so his work was ignored, but he was getting quite close
Criticised because...
Groups contained elements that didn't have similar
properties - eg. carbon and titanium
Mixed up metals and
non-metals - eg. oxygen
and iron
Didn't leave gaps for elements that haven't been discovered yet
Dmitri Mendeleev left gaps and predicted new elements
In 1869, Mendeleev from Russia had 50
known elements and arranged them with
various gaps
Put his elements into order of atomic mass, but left gaps to keep
elements with similar properties in the same vertical groups
The gaps were the clever bit as they predicted the properties of
undiscovered elements - eventually found and fitted the pattern