Mercury is a silvery liquid metal at room temperature. It is a dense, toxic transition metal that forms amalgams with many metals and has historically been used in thermometers, barometers, and electrical switches.
Mercury remains a liquid at room temperature due to weak metallic bonding. The filled 6s2 electrons experience relativistic contraction, reducing overlap between atoms and weakening the bonding strength. As a result, mercury’s melting point is extremely low (−38.83 °C).
The electron configuration of mercury is [Xe] 4f14 5d10 6s2. The completely filled 5d and 6s orbitals make mercury chemically stable and less reactive compared to other transition metals.
Mercury expands and contracts uniformly with temperature changes, making it ideal for measuring temperature and pressure. Its high density and visibility, combined with a wide liquid range (−38.83 °C to 356.73 °C), make it perfect for use in thermometers, barometers, and manometers.
An amalgam is an alloy formed by mercury with another metal. Mercury can form amalgams with metals like gold, silver, and zinc, but not with iron. For example, it dissolves gold to form a gold amalgam used in extraction and dental fillings:
\(\mathrm{Au(s) + Hg(l) \rightarrow Au\text{-}Hg(amalgam)}\)
Mercury is highly toxic because it can vaporize at room temperature, and its vapor can be inhaled easily. Organic compounds like methylmercury (CH3Hg+) accumulate in living organisms, damaging the brain, kidneys, and nervous system. Chronic exposure can lead to mercury poisoning, also known as Minamata disease.
Mercury exhibits two common oxidation states: +1 and +2. In the +1 state, mercury exists as a dimeric cation \(\mathrm{Hg_2^{2+}}\), found in compounds like mercurous chloride (Hg2Cl2), while in the +2 state, it forms mercuric compounds like HgCl2.
\(\mathrm{Hg_2^{2+} \rightarrow 2\,Hg^{2+} + 2e^-}\)
Due to its toxicity and environmental hazards, mercury has been phased out from most medical and laboratory instruments. Digital thermometers and alcohol-based alternatives are now preferred because they are safer and eco-friendly.
Although its use has declined, mercury is still employed in:
Mercury is a dense (13.534 g/cm³), shiny, and mobile liquid metal with a high surface tension. It has a melting point of −38.83 °C and a boiling point of 356.73 °C. It conducts electricity well but poorly conducts heat compared to other metals.
When mercury reacts with chlorine gas, it forms mercuric chloride (HgCl2), a white crystalline solid:
\(\mathrm{Hg(l) + Cl_2(g) \rightarrow HgCl_2(s)}\)
This compound is used in chemical laboratories and as a disinfectant (historically, but now largely discontinued due to toxicity).