4 big orbitals: s, p, d, f
The s-block elements occupy groups 1 and 2.
Elements in group 13 to 18 are p-block elements.
The d-block consists of the elements in group 3 to 12.
Elements in the f-block are found at the lanthanides and actinides
Note: ll electrons in the highest occupied main energy level of an atom (the valence shell) are considered to be valence electrons, even though they may be in different sub-levels.
Note: Each single orbital can be filled max. 2 electrons, the electrons will fill each orbital 1 electron first and then fill the second one after all the orbitals have 1 electron.
The filling order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, ...
