Lead is a chemical element with the symbol Pb (from the Latin plumbum) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and it also has a relatively low melting point. When freshly cut, lead is silver with a hint of blue; Fogs to a dull gray color when exposed to air. Lead has the highest atomic number of any stable element and three of its isotopes are end points of major nuclear decay chains of heavier elements.
Lead is a relatively unreactive post-transition metal. Its weak metallic character is illustrated by its amphoteric nature; Lead and lead oxides react with acids and bases and tend to form covalent bonds. Lead compounds are generally in the +2 oxidation state rather than the +4 state common with the lighter members of the carbon group. The exceptions are mainly limited to organic lead compounds. Like the lighter members of the group, lead tends to bond with itself; it can form chains and polyhedral structures.
Since lead is easily extracted from its minerals, the prehistoric peoples of the Near East knew this. Galena is a major lead mineral that often produces silver. Interest in silver helped initiate the widespread extraction and use of lead in ancient Rome. Lead production declined after the fall of Rome and did not reach comparable levels until the Industrial Revolution. In 2014, the global annual production of lead was approximately 10 million tons, more than half of which came from recycling. Lead's high density, low melting point, ductility, and relative inertia to oxidation make it useful. These properties, combined with its relative abundance and low cost, resulted in its extensive use in construction, plumbing, batteries, bullets and pellets, weights, solders, pewter, fusible alloys, white paints, leaded gasoline, and radiation protection.
In the late 19th century, the toxicity of lead was recognized and its use in many applications has since been phased out. However, many countries still allow the sale of products that expose humans to lead, including some types of paints and bullets. Lead is a neurotoxin that accumulates in soft tissues and bones; it damages the nervous system and interferes with the function of biological enzymes, causing neurological disorders such as brain damage and behavior problems. Lead also affects general health, the cardiovascular and kidney systems.
Physical properties
Atomic
A lead atom has 82 electrons, arranged in an electron configuration of [Xe] 4f145d106s26p2. The sum of the first and second ionization energies of lead (the total energy required to remove the two 6p electrons) is close to that of tin, lead's upper neighbor in the carbon group. This is unusual; Ionization energies generally go down a group, as an element's outer electrons become more distant from the nucleus and more protected by smaller orbitals.
The similarity of ionization energies is due to the contraction of lanthanide: the decrease in the radii of the elements from lanthanum (atomic number 57) to lutetium (71), and the relatively small radii of the elements from hafnium ( 72) onwards. This is due to poor shielding of the nucleus by the 4f lanthanide electrons. The sum of the first four ionization energies of lead exceeds that of tin, [3] contrary to what periodic trends would predict. Relativistic effects, which become significant at heavier atoms, contribute to this behavior. [A] One of those effects is the inert pair effect: the 6s electrons in lead become reluctant to participate in the bond, making the distance between the closest atoms in crystalline lead unusually long. . [5]
The congeners of the lighter carbon group of lead form stable or metastable allotropes with the tetrahedrally coordinated and covalently bonded cubic diamond structure. The energy levels of its outer s and p orbitals are close enough to allow mixing into four hybrid sp3 orbitals. In lead, the inert pair effect increases the separation between its s and p orbitals, and the gap cannot be bridged by the energy that would be released by additional bonds after hybridization. [6] Instead of having a cubic diamond structure, lead forms metallic bonds in which only the p electrons are delocalized and shared between the Pb2 + ions. Consequently, lead has a face-centered cubic structure [7] like the divalent metals of