Question

why the electronic configuration of copper is 3D 10 4 S1 why not 4 x 239

Answer 1

For copper? Because the 3d orbitals are significantly lower in energy for copper (thus making a doubly-occupied 4s orbital unfavorable enough!), AND because it can fill all the quantum states available in the n=3 quantum level, as seen in its electron configuration of:

[Ar]3d104s1

So, it's only natural for copper to "prefer" filling its 3d orbitals rather than its 4s.

Consider the data here (Appendix B.9):

E4s,Cu=−8.42 eVE3d,Cu=−13.47 eV

The 3d orbitals of copper are about 5.05 eV of energy lower than the 4s orbitals of copper (which is about 487 kJ/mol, almost 5 times the strength of a chemical bond!).

You can see the significant increase in favorability when you look at the big picture (graphed from the data here [Appendix B.9]), and see that the 3d orbitals drop in energy faster than the 4s orbitals do as the atomic number increases:

So, copper would have a more stable electron configuration by

filling its 3d orbitals to occupy all possible n=3 quantum states.taking advantage of the particularly low 3d orbital energies compared to the 4s orbital.