The orbital notation or electron configuration for potassium is 1s2 2s2 2p6 3s2 3p6 4s1 or 2, 8, 8 and 1 electrons per shell. The atomic number of potassium is 19, and thus it has 19 electrons and 19 protons.
Each shell is divided into subshells labeled s, p, d and f. The first shell contains two electrons, while the eight electrons in the second shell are distributed in two subshells: two electrons in the s-subshell and six in the p-subshell. The third shell has eight electrons distributed in a similar manner. The fourth shell has one electron in the s-subshell.
The single electron in the last shell is called the valence electron and gives potassium a valency of 1. Potassium readily gives away this single electron to form a positively charged potassium ion.