# Question #d20c4

As the Bohr model diagram below shows, Sodium has 11 protons and 12 neutrons in the nucleus to make the mass number 23. The 11 electrons necessary to make Sodium neutral (protons = electrons) are arranged in a pattern of 2-8-1. Two electrons in the first shell $\left(1 {s}^{2}\right)$, eight electrons in the second shell $\left(2 {s}^{2} 2 {p}^{6}\right)$ and one electron in the outermost shell $\left(3 {s}^{1}\right)$. It is this electron that is all by itself in the outermost shell that is the valence electron.