* Valence electrons are the electrons in the outermost energy level of an atom.
* Electron configuration tells us how electrons are distributed among energy levels and sublevels.
In the configuration 1s² 2s² 2p⁶ 3s² 3p³, the outermost energy level is the third energy level (n=3). This level contains the 3s and 3p sublevels.
* 3s²: There are 2 electrons in the 3s sublevel.
* 3p³: There are 3 electrons in the 3p sublevel.
Therefore, the total number of valence electrons is 2 + 3 = 5.
