Arranged in columns called groups (1-8/0) with a block of transition metals in between. Elements in groups share similar properties and have same number of electrons in outer shell
Arranged in periods
Mendeleev’s Table
Arranged in increasing atomic weight - this could go wrong due to isotopes
Switched order of specific elements to fit patterns - this was due to isotopes as well
Realised some elements hadn’t been discovered so he left gaps
Predicted properties of these based on properties of the groups
These later matched observations so it was accepted
Group 0 had not been discovered
Early Periodic Table
Arranged in increasing atomic weight
Every 8th element react in similar ways - Law of octaves
However always sticking to this law meant that some metals were grouped together that shouldn’t be