Читать книгу Foundations of Chemistry - Philippa B. Cranwell - Страница 75

has atomic number 19 and mass number 39, therefore in a neutral atom there are 19 protons, 19 electrons, and 20 neutrons.

Starting at the lowest energy level, electrons are placed in the energy levels in order of increasing energy. When the third shell is reached, the electrons are firstly placed in the 3s orbital, as this is the lowest energy in the third shell, followed by six electrons in the 3p orbitals. There is one electron left over, and this is put into the 4s orbital because this is lower in energy than the 3d orbitals. This explains why potassium is an s‐block element, as the highest energy electron is in an s orbital.

The ground state electronic configuration of potassium can be written as 1s²2s²2p⁶3s²3p⁶4s¹ or [Ar] 4s¹.