Mercury(II) oxide

Mercury(II) oxide (HgO) is a red or yellow inorganic solid composed of mercury and oxygen. Heating it releases oxygen and leaves elemental mercury.

Thermal decomposition: The breakdown of a compound into simpler substances caused by heating. Heating HgO separates it into elemental mercury and oxygen.
Mercury(II): The +2 oxidation state of mercury, commonly found in compounds containing Hg²⁺. The name identifies mercury’s +2 state in HgO.
Mercury battery: A primary electrochemical cell that uses mercury(II) oxide as its cathode material. HgO supplied the cathode reaction in compact, long-lasting cells.
Mercury poisoning: Illness caused by exposure to elemental mercury or its toxic compounds. Handling or heating HgO can expose people to hazardous mercury.
Oxygen: A chemical element with symbol O and atomic number 8, essential to respiration and combustion. Oxygen gas is one product of HgO decomposition.
Oxide: A binary compound of oxygen with another element, or an oxygen-containing anion. HgO pairs mercury with oxygen in the oxide form.
Primary cell: An electrochemical cell designed for use until its reactants are exhausted, rather than recharging. Mercury batteries are one historically significant use of HgO.
Mercury vapor: Gaseous elemental mercury that can be inhaled and absorbed into the body. Heating HgO can release mercury vapor along with oxygen.
Mercury: A dense, silvery metallic element with symbol Hg and atomic number 80. Elemental mercury remains when HgO decomposes.
Ionic bonding: Chemical bonding driven primarily by electrostatic attraction between oppositely charged ions. The ionic model describes HgO as containing mercury and oxide ions.

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Dichlorine monoxideRelated: HgO reacts with chlorine to produce dichlorine monoxide while binding oxygen from the oxide.