- The classification of Group and Period are totally related to the electron arrangement of the atoms. As shown in the table above, the classification of elements in a periodic table is as follows:
- All the elements in a same group have equal number of valence electron(s) (outer most electron)
- All the elements in a same period have equal number of electron shell(s) (orbit).
- For example, the electron arrangement of calcium is 22.214.171.124. It has 2 valence electron and 4 electron shell. Therefore, it is placed in Group 2, period 4.
- Hydrogen, the simplest element atom, with 1 electron, does not fit into any group. (Even though some of the periodic table place it in Group 1, due to its 1 (and the only one electron) valence electron.
|Number of Valence Electron in a Group|
Number of Valence Electron