Inner-Transition Metals
Definition and meaning of Inner-Transition Metals in chemistry.
Inner-transition metals are the f-block elements of the periodic table, comprising the lanthanide series and the actinide series, in which the highest-energy electrons occupy 4f or 5f orbitals rather than d orbitals.
In more detail
These 28 elements are placed in two rows below the main body of the periodic table to keep the table compact, even though they belong between group 3 and group 4 in order of atomic number. The lanthanides (cerium through lutetium, filling 4f orbitals) are mostly silvery, reactive metals with very similar chemical properties because their 4f electrons are shielded and rarely involved in bonding. The actinides (thorium through lawrencium, filling 5f orbitals) are all radioactive, and only thorium and uranium occur in significant natural abundance; the rest are synthesized in reactors or accelerators.
Key facts
| Field | Inorganic Chemistry |
|---|---|
| Lanthanide series | Z = 58-71, fill 4f orbitals |
| Actinide series | Z = 90-103, fill 5f orbitals |
| Block | f-block |
Uranium (U), an actinide inner-transition metal, has the electron configuration [Rn] 5f3 6d1 7s2 and is used as nuclear reactor fuel because of its fissile isotope U-235.
Frequently asked questions
Why are inner-transition metals shown separately from the main periodic table?
They are set apart purely for layout convenience. Including all 28 f-block elements in their true numerical position would make the periodic table impractically wide, so they are printed as two rows below the main body.
Are lanthanum and actinium inner-transition metals?
Lanthanum and actinium are technically d-block elements (their last electron enters a d orbital), but they are commonly grouped with the lanthanides and actinides because of very similar chemical behavior.