The group number in the periodic table represents number of valence electrons of the elements in a certain group.
Explanation:
There are s, p, d, and f blocks, which you can see in periodic table
The s-block and p-block together are usually considered main-group elements, the d-block corresponds to the transition metals, and the f-block encompasses nearly all of the lanthanides (like lanthanum) and the actinides (like actinium)
There are three main principles, which may useful for you:
The Pauli exclusion rule basically says that at most, 2 electrons are allowed to be in the same orbital.
Hund’s rule explains that each orbital in the subshell must be occupied with one single electron first before two electrons can be in the same orbital.
The Aufbau process describes the process of adding electron configuration to each individualized element in the periodic table.
