Up to the eighteenth element – argon – the filling of the electron shells occurs in accordance with the basic rule: first, shells with lower values of the principal quantum number are filled, then shells with larger values. However, when filling the shells of the nineteenth and twentieth elements – potassium and calcium – deviations from this rule are observed.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.