Asked by Marie

Why is there a big space in the periodic table between the 2nd & 3rd periods? The activity of the electrons is related somehow.
Answered by bobpursley
3d level starts in the fourth period. There is no d filling in the second or first period

1s
2s...2P
3s...3p
4s3d4p
Answered by GK
I think you mean big spaces IN the 2nd and 3rd periods. There are no elements in columns #3 to #12 because there is no "2d" subshell of electrons. Also because the energy of the 3d subshsell is higher than that of the "4s" subshell.
The first row of elements that contains "d" subshell electrons is the 4th row, atomic numbers 11 to 20. In that range the 3d subshell gradually fills up as we go from Sc to Zn. There are no "d" subshells below 3d and no "d-block" elements in the first three rows.
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