The Periodic Table / groups and periods
As already said in module 01 about atoms: their most characterizing data are the number of electronic main levels and the number of electrns in the outer shell (the valency electrons).
The number of main levels can vary from 1 to 7, what coincides with the seven periods of the Periodic Table.
The number of valency electrons can vary from 1 to 8, what coincides with the number of main groups of the PT.
With these two data you can determine the position of an element in the PT.