Valency of Mercury (Hg)
Mercury shows variable valency — most commonly 1 and 2 — because it is a d-block element whose outer electrons can join bonding in more than one way.
Teachers call it "one fact, fully handled" — exactly what this page does for Mercury. The answer sits at the top in bold; scroll for the working, the shell-by-shell breakdown and the two questions students ask most. Need the whole picture instead — history, characteristics, uses, exam questions? The full Mercury page is one click away.
Counting the valence electrons
From the configuration [Xe] 4f^14 5d^10 6s^2, Mercury's outermost shell carries 2 electrons. For a d-block element the nearby inner "d" subshell can also lend electrons, which is where variable valency comes from.
Position check: Mercury belongs to group 12 of the periodic table, period 6.
Why Mercury has more than one valency
The common valencies are 1 and 2. Both the outer s electrons and the nearby (n−1)d electrons sit close in energy, so Mercury can offer different numbers of them in different compounds — giving ions such as Hg¹⁺ and Hg²⁺ and families of compounds like Hg₁X₂ / HgX.
Valency vs valence electrons
Valence electrons are what you count (2 for Mercury); valency is what the atom will do to complete its outer shell (1 and 2 here). Keep the two words straight and half the periodic-table chapter writes itself.
Students also ask
How do I find the valency of Mercury from its group?
Mercury sits in group 12; for this transition group the safe exam answer is its common valency, 1 and 2.
Why does Mercury show variable valency?
Because both its outer shell and the nearby inner subshell can participate in bonding, Mercury forms more than one stable ion — hence valencies 1 and 2.