Here's why:

* Valence Electrons: These are the electrons in the outermost shell of an atom, which are involved in chemical bonding.

* Electron Configuration: This describes the arrangement of electrons in an atom's energy levels.

* 2s²: This means that there are two electrons in the 2s orbital, which is the outermost shell for beryllium.

Let me know if you'd like to explore more about electron configurations or other elements!