Chemistry · Ch 4 — The d- and f-Block Elements
Position in the Periodic Table
Position in the Periodic Table
Where the d-Block Sits
The d-block forms the large middle section of the periodic table. It is sandwiched between the s-block on the left and the p-block on the right. Elements land in this block because electrons are being added into the d-orbitals of the penultimate (second-to-outermost) energy level of the atom, rather than into the outermost shell.
"Penultimate" here means one shell in from the outermost occupied shell. For an atom filling its 3d orbitals, for instance, the outermost occupied shell is already the 4th (4s), so the d-orbitals being filled belong to the shell just below it.
Four Series of Transition Metals
This filling of the penultimate d-orbitals happens four separate times as we move down the periods, giving four horizontal rows of transition metals:
- 3d series — the first row
- 4d series — the second row
- 5d series — the third row
- 6d series — the fourth row
Each series is simply the stretch of elements across a period where the corresponding d sub-shell is being progressively filled.
Continuity with Non-Transition Element Theory
Transition elements and their compounds are conventionally studied as their own group, separate from the non-transition (s- and p-block) elements, because of the distinctive behaviour their partly filled d-orbitals produce. Even so, the general theory of valence developed for non-transition elements carries over and applies successfully to transition elements as well — the d-block is not a completely different system of chemistry, just one with extra features layered on top.