Multi-Electron Atoms in the Mendeleev Periodic Table

Multi-Electron Atoms in the Mendeleev Periodic Table 

The Table 3.2 shows the capacity of the electron shells of elements. Note that the values in the third column are not ordered by n, there are some swaps. For example, a 4s-electron has less energy than a 3d-eleclron and a 5s-electron has less energy than a 4d-electron. One can say the same about 6s and 4f, 6s and 5d, 7s and 6d. This fact is due to the effect of orbital quantum number I = 0 on the electron energy, which we have considered in previous section. 

In the hydrogen atom, the single electron occupies the Is shell. For the helium atom both electrons are in the Is shell. The spins of electrons are directed oppositely. The 2s shell is fiUed in Uthium and beryllium. 

The upper index on the left of the element symbol is its number in the Mendeleev periodic system as well as the number Z of protons in the nucleus. 

The electrons fill the 2p-shell in sequence in the next six elements. 

---