ABSTRACT
The effective nuclear charge, Z*, is given by Z-cr, where a is the sum of the shielding contributions of all the other electrons in the atom, as follows Principal quantum number, n, of shielding electrons
Shielding contribution,
n higher than principal quantum number of the electron under consideration
n equal to principal quantum number of the electron under consideration
n is one less than the principal quantum number of the electron under consideration (a) for an s or p electron under consideration (b) for a d or f electron under consideration
n is less by two, or more, than the principal quantum number of the electron under consideration
Zero
0.35 (for each electron) except that 0.30 is used for a for a Is electron acting on the second Is electron
0.85 1.00 1.00
In hydrogen-like atoms, the p orbital has the same energy as the s orbital with the same value of n, but in all atoms with more than one electron, shielding effects come into play. The p orbital is more shielded than the corresponding s orbital as it does not penetrate so far towards the nucleus. It accordingly experiences a smaller effective nuclear charge and is of higher energy. The curves of p orbital energies versus atomic number run roughly parallel with the curves of the corresponding s orbitals as/increases (Fig. 8.1). The gap in energy between the s and p orbital of a given n value is much smaller than that separating the p orbital and the s orbital with the next higher n value.
