Give the number of s, p, d, and f electrons in each of the following atoms.

Question

Cd(Z=48)

Fr(Z=87)

Cr(Z=24)

Answer 1

Assuming you refer to only valence electrons and not all of the core electrons as well...

There is a short way and a long way of doing this. I'll provide both.

Short method: Look in the periodic table and use s-block, p-block, d-block and f-block information

Cd(Z=48). In the periodic table it is a d-block element and is the 10th one, so has 10 d electrons

Fr(Z=87). In the periodic table it is an s-block element and is the 1st one, so has 1 s electron.

Cr(Z=24). In the periodic table it is a d-block element and is the 4th one, so expected to have 4 d electrons.

BUT, it is more stable if the d orbital is half full so a 4s electron moves and it now has 5 d electrons.

Long method: Write out the electron configuration:

Cd(Z=48). [Kr]5s²4d¹⁰

Fr(Z=87). [Rn]7s¹

Cr(Z=24). [Ar]4s¹3d⁵