Zusammenfassung der Ressource
History of the Periodic Table
- 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
Anmerkungen:
- 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
Anmerkungen:
- 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
Anmerkungen:
- 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