Valency of Cerium (Ce)
Cerium shows variable valency — most commonly 3 and 4 — because it is a f-block element whose outer electrons can join bonding in more than one way.
This is the fast lane: one page, one fact, zero digressions. Read the quick answer, check the table, and if your exam needs the full derivation, the sections below walk through it step by step — in Bangla and English, like every page here. Need the whole picture instead — history, characteristics, uses, exam questions? The full Cerium page is one click away.
Counting the valence electrons
From the configuration [Xe] 4f¹ 5d¹ 6s², Cerium's outermost shell carries 2 electrons. For a f-block element the nearby inner "f" subshell can also lend electrons, which is where variable valency comes from.
Position check: Cerium belongs to the f-block of the periodic table, period 6.
Why Cerium has more than one valency
The common valencies are 3 and 4. Both the outer s electrons and the nearby (n−1)d electrons sit close in energy, so Cerium can offer different numbers of them in different compounds — giving ions such as Ce³⁺ and Ce⁴⁺ and families of compounds like Ce₃X₂ / Ce₄X₂.
Valency vs valence electrons
Valence electrons are what you count (2 for Cerium); valency is what the atom will do to complete its outer shell (3 and 4 here). Keep the two words straight and half the periodic-table chapter writes itself.
Students also ask
How do I find the valency of Cerium from its group?
As an f-block element Cerium is not assigned a group; examiners accept its common valency of 3 and 4.
Why does Cerium show variable valency?
Because both its outer shell and the nearby inner subshell can participate in bonding, Cerium forms more than one stable ion — hence valencies 3 and 4.