The identity of an element is determined by its atomic number, which represents the count of protons within the nucleus. In a neutral atom, the number of electrons orbiting the nucleus equals the number of protons. Therefore, an atom possessing 80 electrons must have an atomic number (Z) of 80.
The Significance of 80 Electrons
The element with an atomic number of 80 is Mercury (Hg), derived from the ancient Greek hydrargyrum, meaning “water-silver.” This places Mercury in Group 12 and Period 6 of the periodic table, classifying it as a transition metal. The 80 electrons are arranged in six shells, with two electrons in the outermost shell. This configuration contributes to its unique chemical behavior and relatively low melting point compared to other metals.
Unique Physical and Chemical Characteristics
Mercury is the only metallic element that is liquid at standard temperature and pressure. It has an exceptionally low melting point of -38.83 °C and a boiling point of 356.73 °C, giving it a wide liquid range.
Mercury is notable for its extremely high density, approximately 13.5 times that of water. It also exhibits high surface tension, causing it to form distinct, rounded droplets.
Despite being a poor conductor of heat, mercury is a fair conductor of electricity. It readily dissolves other metals like gold and silver to form alloys called amalgams. Iron is an exception, which is why the metal was historically transported in iron flasks. The unusual liquid state of mercury is attributed to relativistic effects influencing the bonding of its outer electrons.
Historical and Modern Applications
For centuries, mercury’s unique properties made it useful, earning it the nickname “quicksilver.” Its consistent volume expansion across a wide temperature range made it ideal for early scientific instruments like thermometers and barometers. Historically, mercury compounds were used in medicine and in felt-making, which led to the neurological disorders observed in “mad hatters.”
The amalgamation property was exploited extensively in gold mining to extract gold from ore. In modern technology, mercury vapor is used in fluorescent lamps, where an electrical discharge causes it to emit ultraviolet light. Though its use is declining due to toxicity concerns, mercury remains present in dental amalgams and specialized electrical switches.
Environmental Presence and Health Risks
Mercury is naturally occurring, but human activities like coal burning, waste incineration, and industrial processes are the primary sources of its environmental release. Once released, elemental mercury travels globally in the atmosphere before settling in aquatic environments. In water and sediment, microorganisms convert inorganic mercury into methylmercury, the most toxic organic form.
Methylmercury is readily absorbed and not easily excreted by organisms, leading to bioaccumulation and biomagnification up the food chain. This results in the highest concentrations in large, predatory fish, which is the main route of human exposure. Mercury compounds are neurotoxins that damage the nervous, digestive, and immune systems. Exposure poses a particular threat to the developing brain of a fetus and young children, potentially causing severe neurological deficits.