Mercury(I) ion (Hg₂²⁺)
- Charge
- +2
- Atoms
- Hg × 2
- Atoms in total
- 2
- Mass of the ion
- 401.18 g/mol
The mercury(I) ion is two mercury atoms joined by a metal–metal bond, with a 2+ charge in total. Each mercury atom has lost one electron, giving it a +1 oxidation state, and the bond between them keeps the pair together in its compounds. You meet it mainly in calomel, mercury(I) chloride, the compound inside the calomel reference electrode long used in pH and voltage measurements.
- The Roman numeral I gives each mercury atom’s oxidation state, +1, even though the ion carries 2+, so mercury(I) chloride is Hg₂Cl₂, not HgCl.
- Mercury(II), Hg²⁺, is a single atom with a 2+ charge and forms different compounds, such as HgCl₂.
- It is one of the very few common metal cations made of two bonded atoms of the same element.
Compounds that contain mercury(I)
Hg2Cl2 Mercury(I) chloride
Hg2(NO3)2 Mercury(I) nitrate
Hg2SO4 Mercury(I) sulfate