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Line 8: Lead is a relatively unreactive [[post-transition metal]]. Its weak metallic character is illustrated by its [[amphoteric]] nature; lead and [[lead oxide]]s react with [[acid]]s and [[base (chemistry)|bases]], and it tends to form [[covalent bond]]s. [[Chemical compound|Compounds]] of lead are usually found in the +2 [[oxidation state]] rather than the +4 state common with lighter members of the [[carbon group]]. Exceptions are mostly limited to [[organolead compound]]s. Like the lighter members of the group, lead tends to [[chemical bond|bond]] with itself; it can form chains, rings and polyhedral structures. Lead is easily extracted from its [[ore]]s; prehistoric people in Western Asia [[metals of antiquity|knew of it]]. [[Galena]], a principal ore of lead, often bears [[silver]], interest in which helped initiate widespread extraction and use of lead in [[ancient Rome]]. Lead production declined after the [[Fall of the Western Roman Empire|fall of Rome]] and did not reach comparable levels until the [[Industrial Revolution]]. In 2014, annual global production of lead was about ten million tonnes, over half of which was from recycling. Lead's high density, low melting point, [[ductility]] and relative inertness to [[oxidation]] make it useful. These properties, combined with its relative abundance and low cost, resulted in its extensive use in construction, [[plumbing]] In the late 19th century, [[lead poisoning|lead's toxicity]] was recognized, and its use has since been phased out of many applications. Lead is a [[neurotoxin]] that accumulates in soft tissues and bones, damages the [[nervous system]], and causes blood disorders. It is particularly problematic in children, in that permanent brain damage may result, even if blood levels are promptly [[Chelation therapy|normalized with treatment]]. | |||