f-Block Elements
The lanthanides and actinides, in which electrons fill the f orbitals of the antepenultimate shell.
Formula / equation
(n−2)f¹⁻¹⁴
Unit
Dimensionless
In depth
Because f electrons are buried deep inside the atom, the fourteen lanthanides are chemically almost indistinguishable, all favouring the +3 state, and were historically very hard to separate. Poor f-orbital shielding produces the lanthanide contraction, which makes the third-row transition metals unexpectedly small.
Examples in the real world
Neodymium in permanent magnets, europium in red phosphors, and uranium and plutonium among the actinides.