- Lead (Pb) is a heavy post-transition metal with atomic number 82, belonging to Group 14 of the periodic table, alongside carbon, silicon, germanium, tin, and flerovium.
- Its electron configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p², giving it four valence electrons. Lead commonly exhibits oxidation states of +2 and +4, though the +2 state is far more stable due to the inert pair effect. Each atom of lead contains eighty-two protons, eighty-two electrons, and usually between 122 and 126 neutrons depending on the isotope.
- Naturally occurring lead consists of four stable isotopes—lead-204 (²⁰⁴Pb), lead-206 (²⁰⁶Pb), lead-207 (²⁰⁷Pb), and lead-208 (²⁰⁸Pb), with ²⁰⁸Pb being the most abundant and notably stable as a “doubly magic” nucleus.
- Lead has been known since antiquity and was widely used by ancient civilizations such as the Egyptians, Greeks, and Romans. The Romans, in particular, employed it extensively in plumbing, water pipes, and storage vessels, a practice that contributed to widespread lead poisoning. The name lead derives from the Old English lead, while its symbol Pb comes from the Latin plumbum, meaning “soft metal.”
- Physically, lead is a dense, soft, and malleable metal with a bluish-gray appearance that tarnishes to a dull gray upon exposure to air. It has a density of 11.34 g/cm³, a melting point of 327.5 °C (621.5 °F), and a boiling point of 1,749 °C (3,180 °F). Lead is relatively easy to shape, cut, and extrude, and it possesses poor electrical conductivity compared to many other metals. One of its most notable properties is its high resistance to corrosion, which makes it durable in harsh environments.
- Chemically, lead is moderately reactive. It resists attack from sulfuric acid but dissolves in nitric acid, forming lead nitrate [Pb(NO₃)₂]. Lead forms a variety of compounds, including lead(II) oxide (PbO), lead(IV) oxide (PbO₂), and lead(II) sulfide (PbS), the latter being its most common ore mineral, known as galena. Due to the inert pair effect, lead(II) compounds are generally more stable than lead(IV). Lead also forms organolead compounds such as tetraethyllead (Pb(C₂H₅)₄), once widely used as a gasoline additive to improve engine performance.
- Lead has historically had extensive industrial applications. It was used in water pipes, paints, cosmetics, and as a stabilizer in plastics. For much of the 20th century, tetraethyllead was added to gasoline, but its use has been phased out worldwide due to health concerns. Today, lead’s primary uses include lead-acid batteries (vital for automobiles and backup power systems), radiation shielding, cable sheathing, and alloys. Lead glass (commonly known as crystal) is used for decorative items and radiation protection, while lead compounds remain in use in some specialized ceramics and electronics.
- Biologically, lead has no beneficial role and is highly toxic to humans and animals. Lead poisoning can occur through ingestion or inhalation of dust, paint particles, or contaminated water. Chronic exposure damages the nervous system, kidneys, and reproductive system, and it is particularly harmful to children, where it impairs cognitive development and causes behavioral disorders. The neurotoxic effects of lead exposure have made it a major public health concern, leading to widespread regulations that restrict its use in consumer products.
- Environmentally, lead is moderately abundant in Earth’s crust, with an average concentration of about 14 parts per million. It is primarily obtained from the mineral galena (PbS), often in association with zinc and silver ores. Major producers include China, Australia, the United States, and Peru. Lead mining and smelting have historically contributed to significant environmental contamination, though modern regulations have reduced emissions. Nonetheless, legacy pollution from old paints, gasoline, and industrial waste continues to pose risks.
