Question

why there is gap of fourteen elements in second and third transition series ​

Answer 1

Answer:

Because the transition elements are the elements in which d-orbitals fill.

The first two rows are from shells that don’t have d-orbitals; the first set of d-orbitals are in the third shell.

But d-orbitals don’t fill until after the s-orbital of the next shell, that is, 3d don’t fill until after 4s, 4d until after 5s, and so on.

You see the same effect with f-orbitals, which first appear in the #4 shell and don’t fill until after the same shell’s d-orbitals. More specifically, the “n” shell f-orbitals fill after the “n+2” shell’s s-orbitals.

Explanation:

hope it helps you mate

Answer 2

Answer:

1. In the second and third transition series, there are a set of elements in both periods that have f-orbitals.

2. Because of the f-orbital, they cannot be placed with the d-block elements.

3. You can actually see them under the d-block elements as f-block elements.

4. But for the continuity of the period, something must fill the space between the element before and after the series in both periods.

5. So we replaced those series with Lanthanum (La) and Actinium (Ac) like separate elements which you can see in the table.