Answer:
Electron configuration can be carried out in two steps which can be:
Sublevel notation
Shell notations.
In the sublevel notation, the sequence of filling electrons into the orbitals of the sublevels are guided by some principles:
the maximum number of electrons in the orbital of sublevels are two for s-sublevel, six for p-sublevel, ten for d-sublevel and fourteen for f-sublevel. This indicates that the maximum number of electrons in an orbital is two.
Aufbau's prinicple states that sublevel with lower energies are filled up before those with higher energies.
Pauli exclusion principle states that no two electrons in an atom can have the same set of the four quantum numbers.
Hund's rule states that electrons go into degenerate orbitals singly first before pairing occurs.
Using the shell notation, numbers are used to denote the sum of electrons in all orbitals each energy level.
For an atom of Be:
Sublevel notation for the 4 electrons 1s²2s²
Shell notation 2,2
Other representation is using the electron dot structure.