Number of electrons in each Electron configuration?

Answer 1

Period ---- Shell -------------- Atom pairs

1 ------------ s ---------------------- 1

2 ---------- s, p ------------------- 1, 3

3 ---------- s, p ------------------- 1, 3

4 -------- s, p, d ---------------- 1, 3, 5

5 -------- s, p, d ---------------- 1, 3, 5

Each pair represent 2 atoms. The s shell can hold 2 electrons, the p shell can hold 6 electrons, and the p shell can hold 10 electrons. The 3rd shell does not include the d shell since the atoms in the B group begin on the 3rd period

There are also some special configurations in the B group where the s shell lends an electron to the d group such as Cr. For example, if Cr followed the general guidelines that other atoms in the A groups, it would be

1s^2/2s^2 p^6/3s^2 p^6/4s^2 d^5, except it actually is 1s^2...4s^1 d^5

Special guidelines apply to group 5B for period 5 excluding 4, group 6B for periods 4 and 5, group 8B (sub groups 8, 9, and 10) for period 5, and group 1B for periods 4 and 5 (and 6 if you want to count the f subshell), where electrons from the s shell are loaned to the d shell

Answer 2

I assume your asking what the role of the coefficient in an electron configuration is. It represents the orbital, such as n=1 in "1s2".