Mercury



 

Learning Objective

  • Identify mercury based on its physical properties.

Key Points

    • Mercury is the only metal that is liquid at standard conditions for temperature and pressure.
    • Mercury is a poor conductor of heat, but a fair conductor of electricity.
    • Mercury has a unique electron configuration which strongly resists removal of an electron, making it behave similarly to noble gas elements. As a result, mercury forms weak bonds and is a liquid at room temperature.
    • Mercury dissolves to form amalgams with gold, zinc, and many other metals.

Term

  • amalgamAn alloy containing mercury.

Properties of Mercury

Mercury is a dense, silvery d-block element. It is the only metal that is liquid at standard conditions for temperature and pressure. The only other element that is liquid under these conditions is bromine, though metals such as caesium, gallium, and rubidium melt just above room temperature. With a freezing point of −38.83 °C and boiling point of 356.73 °C, mercury has one of the narrowest liquid state ranges of any metal. Mercury occurs in deposits throughout the world mostly as cinnabar (mercuric sulfide), an ore that is highly toxic by ingestion or inhalation. Mercury poisoning can also result from exposure to water-soluble forms of mercury (such as mercuric chloride or methylmercury), inhalation of mercury vapor, or ingestion of seafood contaminated with mercury.

Compared to other metals, mercury is a poor conductor of heat, but a fair conductor of electricity. Mercury has a unique electronic configuration which strongly resists removal of an electron, making mercury behave similarly to noble gas elements. The weak bonds formed by these elements become solids which melt easily at relatively low temperatures.

MercuryMercury is a silvery metal that is liquid at standard temperature and pressure (STP).

Reactivity and Amalgams

Mercury does not react with most acids, although oxidizing acids such as concentrated sulfuric acid and nitric acid dissolve it to give sulfate, nitrate, and chloride salts. Like silver, mercury reacts with atmospheric hydrogen sulfide. Mercury even reacts with solid sulfur flakes, which are used in mercury spill kits to absorb mercury vapors.

Mercury dissolves to form amalgams with gold, zinc, and many other metals. Iron is an exception, and iron flasks have been traditionally used to trade mercury. Sodium amalgam is a common reducing agent in organic synthesis, and it is also used in high-pressure sodium lamps. Mercury readily combines with aluminium to form a mercury-aluminium amalgam when the two pure metals come into contact. Since the amalgam destroys the aluminium oxide layer which protects metallic aluminium from oxidizing, even small amounts of mercury can seriously corrode aluminium. For this reason, mercury is not allowed aboard an aircraft under most circumstances because of the risk in forming an amalgam with exposed aluminium parts.

Uses of Mercury

Mercury is used in thermometers, barometers, manometers, float valves, mercury switches, and other devices. Concerns about the element’s toxicity have led to mercury thermometers being largely phased out in clinical environments in favor of alcohol-filled instruments. Mercury is still used in scientific research and as amalgam material for dental restoration. It is also used in lighting—electricity passed through mercury vapor in a phosphor tube produces short-wave ultraviolet light, causing the phosphor to fluoresce and produce visible light.