Question

Why d block elements are called outer transition elements? Concisely please.

Answer 1

Refer to the explanation.

Explanation:

The d-block elements are the outer transition elements as opposed to the f-block, which are the inner transition elements. The inner transition elements are part of group 3, and are the elements with atomic numbers `57-71` in period 6, and the elements with the atomic numbers `89-103` in period 7. So the inner transition elements are between group 2 and group 4 in periods 6 and 7.

The following picture is an extended periodic table, which includes the inner transition (f-block) elements in two shades of purple. The d-block (light blue) comes after the inner transition elements, so this illustrates why the f-block elements are called the inner transition elements.