Lead

Jai Ganesh · Today 17:30:11

Lead

Gist

Lead is a chemical element with the symbol Pb and atomic number 82. It is a heavy, dense, and soft metal known for being malleable, corrosion-resistant, and having a low melting point. Historically, lead was used in water pipes, leading to the terms "plumbing" and "plumber" from its Latin name, plumbum. While it is a stable element, it is also highly toxic and should be handled and disposed of with care.

Lead and lead compounds have been used in a wide variety of products found in and around our homes, including paint, ceramics, pipes and plumbing materials, solders, gasoline, batteries, ammunition and cosmetics

Summary

Lead is a chemical element with the symbol Pb (from the Latin plumbum) and atomic number 82. It is a heavy metal denser than most common materials. Lead is soft, malleable, and has a relatively low melting point. When freshly cut, it appears shiny gray with a bluish tint, but it tarnishes to dull gray on exposure to air. Lead has the highest atomic number of any stable element, and three of its isotopes are endpoints of major nuclear decay chains of heavier elements.

Lead is a relatively unreactive post-transition metal. Its weak metallic character is shown by its amphoteric behavior: lead and lead oxides react with both acids and bases, and it tends to form covalent bonds. Lead compounds usually occur in the +2 oxidation state rather than the +4 state common in lighter members of the carbon group, with exceptions mostly limited to organolead compounds. Like the lighter members of the group, lead can bond with itself, forming chains and polyhedral structures.

Easily extracted from its ores, lead was known to prehistoric peoples in the Near East. Galena is its principal ore and often contains silver, encouraging its widespread extraction and use in ancient Rome. Production declined after the fall of Rome and did not reach similar levels until the Industrial Revolution. Lead played a role in developing the printing press, as movable type could be readily cast from lead alloys. In 2014, annual global production was about ten million tonnes, over half from recycling. Lead's high density, low melting point, ductility, and resistance to oxidation, together with its abundance and low cost, supported its extensive use in construction, plumbing, batteries, ammunition, weights, solders, pewter, fusible alloys, lead paints, leaded gasoline, and radiation shielding.

Lead is a neurotoxin that accumulates in soft tissues and bones. It damages the nervous system, interferes with biological enzymes, and can cause neurological disorders ranging from behavioral problems to brain damage. It also affects cardiovascular and renal systems. Lead's toxicity was noted by ancient Greek and Roman writers, but became widely recognized in Europe in the late 19th century.

Details

Lead is a chemical element. Its chemical symbol is Pb, which comes from plumbum, the Latin word for lead. Its atomic number is 82, atomic mass is 207.2 and has a melting point of 327.8°C. It is a very poisonous and heavy metal, and is also the ending element to the stable elements, although the next element, bismuth, is so weakly radioactive that it can be considered stable for practical purposes.

Properties:

Physical properties

Lead is a shiny, gray-blue poor metal. It gets tarnished easily to a dull gray color. It is soft and malleable. It is very shiny when it is melted. It is very heavy. It is very corrosion-resistant. It is made stronger by adding antimony or calcium. It can form an alloy with sodium. It is toxic to people and animals when swallowed.

Chemical properties

Lead burns in air with a grayish-white flame, making toxic fumes of lead(II) oxide. Only the surface is corroded by air. It dissolves in nitric acid to make lead(II) nitrate. It does not dissolve in sulfuric or hydrochloric acid. It reacts with sodium nitrate to make lead(II) oxide and sodium nitrite. It reacts with chlorine to make lead(II) chloride. Lead(II) oxide reacts with lead sulfide to make lead metal and sulfur dioxide.

Chemical compounds

Lead makes chemical compounds in two main oxidation states: +2 and +4. +2 compounds, also known as lead(II) compounds or plumbous compounds, are weak oxidizing agents. +4 compounds, also known as lead(IV) compounds or plumbic compounds, are strong oxidizing agents. Lead compounds are toxic just like the element. The lead halides do not dissolve in water. Lead(IV) oxide is the most common lead(IV) compound. It is a black solid. The lead oxides are all colored, while the other salts are white or colorless. Lead nitrate and lead(II) acetate are the soluble compounds of lead.

Mixed oxidation state compounds

Mixed oxidation state compounds contain lead in the +2 and +4 oxidation state.

Occurrence

Lead is found very rarely in the earth's crust as a metal. Normally, lead is in the mineral galena. Galena is lead sulfide. Galena is the main lead ore.

History

Lead was used for thousands of years because it is easy to get from the ground and easy to shape and work with. The Romans used lead very commonly. They used it for pipes, drinking vessels, and fasteners.

Preparation

Lead is made from galena. Galena is made pure by froth flotation to get all the impurities out. Then the lead sulfide is roasted in a furnace to make lead(II) oxide. The lead(II) oxide is heated with coke to make liquid lead metal.

Uses:

As an element

Lead is used in the ballast of sailboats. It is also used in weight belts for scuba diving. It is also used to make shotgun pellets and bullets for small arms. Some printing presses use lead type because it can be easily shaped. It can be used outside because it does not corrode in water.

Lead has been used to make pipes and water ducts, as it is easy to form and cast, and the parts made from lead are easy to fit, and clean water does not corrode lead. The names "plumbing" for waterworks, and "plumber" for a pipe fitter, come from the Latin name of lead, plumbum.

Most lead is used in lead acid batteries, though. The lead is oxidized, making electricity. Sheets of lead are used to block sound in some places. Lead is used in radiation shielding. Molten lead can be used as a coolant in nuclear reactors. It used to be mixed with tin to make the pipes in pipe organs. Different amounts of lead make different sounds. In addition, lead has found its usage in solder.

It is used in some solder. It is used in covering for wires that carry high voltage. Some tennis rackets have lead in them to make them heavier. It is used to balance wheels of cars, to make statues, and to make decorative looks in buildings.

As chemical compounds

Many lead compounds are used to make colored glazes in ceramics. Lead can be used in PVC pipes. Lead compounds are added to candles to make them burn better. Lead glass has lead(II) oxide in it. Lead compounds are still used as pigments in some places. Lead compounds were added to gasoline, but are now outlawed. Some lead compounds are semiconductors and are used in photodetectors.

Old uses

Lead was used in many red, yellow, and white pigments in paints. Lead was also used in pesticides. Lead used to be used in pipes carrying water, but now it is not because lead can leach into the water.

Safety

Although it can be safely touched, exposure to lead should be avoided – it is very toxic to humans and other animals when swallowed, and its use is restricted in many countries.

If someone is exposed to lead for a long time, it ruins their kidneys and gives them abdominal pains. Lead also ruins the nervous system. Lead paint was being eaten by children and they were getting lead poisoning.

The best way to understand lead and its properties is to read its MSDS.

Additional Information

Lead (Pb) is a soft, silvery white or grayish metal in Group 14 (IVa) of the periodic table. Lead is very malleable, ductile, and dense and is a poor conductor of electricity. Known in antiquity and believed by the alchemists to be the oldest of metals, lead is highly durable and resistant to corrosion, as is indicated by the continuing use of lead water pipes installed by the ancient Romans. The symbol Pb for lead is an abbreviation of the Latin word for lead, plumbum.

Element Properties

atomic number : 82
atomic weight : 207.19
melting point : 327.5 °C (621.5 °F)
boiling point : 1,744 °C (3,171.2 °F)
density : 11.29 gram/{cm}^{3} at 20 °C (68 °F)
oxidation states : +2, +4

Occurrence and distribution

Lead is mentioned often in early biblical accounts. The Babylonians used the metal as plates on which to record inscriptions. The Romans used it for tablets, water pipes, coins, and even cooking utensils; indeed, as a result of the last use, lead poisoning was recognized in the time of Augustus Caesar. The compound known as white lead was apparently prepared as a decorative pigment at least as early as 200 bce. Modern developments date to the exploitation in the late 1700s of deposits in the Missouri-Kansas-Oklahoma area in the United States.

On a weight basis, lead has nearly the same abundance in Earth’s crust as tin. Cosmically, there is 0.47 lead atom per 106 silicon atoms. The cosmic abundance is comparable to those of cesium, praseodymium, hafnium, and tungsten, each of which is regarded as a reasonably scarce element.

Although lead is not abundant, natural concentration processes have resulted in substantial deposits of commercial significance, particularly in the United States but also in Canada, Australia, Spain, Germany, Africa, and South America. Significant deposits are found in the United States in the western states and the Mississippi valley. Rarely found free in nature, lead is present in several minerals, but all are of minor significance except the sulfide, PbS (galena, or lead glance), which is the major source of lead production throughout the world. Lead is also found in anglesite (PbSO4) and cerussite (PbCO3). By the early 21st century, China, Australia, the United States, Peru, Mexico, and India were the world’s top producers of lead in concentrate.

Lead may be extracted by roasting the ore and then smelting it in a blast furnace or by direct smelting without roasting. Additional refining removes impurities present in the lead bullion produced by either process. Almost half of all refined lead is recovered from recycled scrap.

Uses of the metal

Only a single crystalline modification, with a close-packed metallic lattice, is known. Properties that are responsible for the many uses of elemental lead include its ductility, ease of welding, low melting point, high density, and ability to absorb gamma radiation and X-radiation. Molten lead is an excellent solvent and collector for elemental silver and gold. The structural applications of lead are limited by its low tensile and fatigue strengths and its tendency to flow even when only lightly loaded.

When freshly cut, lead oxidizes quickly, forming a dull gray coating, formerly thought to be lead suboxide, Pb2O, but now recognized as a mixture of lead and lead monoxide, PbO, which protects the metal from further corrosion. Similarly, although lead is soluble in dilute nitric acid, it is only superficially attacked by hydrochloric or sulfuric acids because the insoluble chloride (PbCl2) or sulfate (PbSO4) coatings that are formed prevent continued reaction. Because of this general chemical resistance, considerable amounts of lead are used in roofing, as coverings for electric cables placed in the ground or underwater, and as linings for water pipes and conduits and structures for the transportation and processing of corrosive substances.

Elemental lead can also be oxidized to the Pb2+ ion by hydrogen ions, but the insolubility of most salts of Pb2+ makes lead resistant to attack by many acids. Oxidation under alkaline conditions is easier to effect and is favoured by the formation of the soluble species of lead in the +2 oxidation state. Lead oxide (PbO2, with lead as the Pb4+ ion) is among the stronger oxidizing agents in acidic solution, but it is comparatively weak in alkaline solution. The ease of oxidation of lead is enhanced by complex formation. The electrodeposition of lead is best effected from aqueous solutions containing lead hexafluorosilicate and hexafluorosilicic acid.

Lead has many other applications, the largest of which is in the manufacture of storage batteries. It is used in ammunition (shot and bullets) and as a constituent of solder, type metal, bearing alloys, fusible alloys, and pewter. In heavy and industrial machinery, sheets and other parts made from lead compounds may be used to dampen noise and vibration. Because lead effectively absorbs electromagnetic radiation of short wavelengths, it is used as a protective shielding around nuclear reactors, particle accelerators, X-ray equipment, and containers used for transporting and storing radioactive materials. Together with the compound lead oxide (PbO2) and with lead-antimony or lead-calcium alloys, it is employed in common storage batteries.

Properties of the element

Lead and its compounds are toxic and are retained by the body, accumulating over a long period of time—a phenomenon known as cumulative poisoning—until a lethal quantity is reached. The toxicity of lead compounds increases as their solubility increases. In children the accumulation of lead may result in cognitive deficits; in adults it may produce progressive renal disease. Symptoms of lead poisoning include abdominal pain and diarrhea followed by constipation, nausea, vomiting, dizziness, headache, and general weakness. Elimination of contact with a lead source is normally sufficient to effect a cure. The elimination of lead from insecticides and paint pigments and the use of respirators and other protective devices in areas of exposure have reduced lead poisoning materially. The recognition that the use of tetraethyl lead, Pb(C2H5)4, as an antiknock additive in gasoline was polluting the air and water led to the compound’s elimination as a gasoline constituent in the 1980s. (For full treatment of lead and lead mining and refining, see also lead poisoning.)

Nuclear properties

Lead is formed both by neutron-absorption processes and the decay of radionuclides of heavier elements. Lead has four stable isotopes; their relative abundances are lead-204, 1.48 percent; lead-206, 23.6 percent; lead-207, 22.6 percent; and lead-208, 52.3 percent. Three stable lead nuclides are the end products of radioactive decay in the three natural decay series: uranium (decays to lead-206), thorium (decays to lead-208), and actinium (decays to lead-207). More than 30 radioactive isotopes have been reported. Of the radioactive isotopes of lead, the following appear as members of the three natural decay series: (1) thorium series: lead-212; (2) uranium series: lead-214 and lead-210; (3) actinium series: lead-211. The atomic weight of natural lead varies from source to source, depending on its origin by heavier element decay.

Compounds

Lead shows oxidation states of +2 and +4 in its compounds. Among the many important lead compounds are the oxides: lead monoxide, PbO, in which lead is in the +2 state; lead dioxide, PbO2, in which lead is in the +4 state; and trilead tetroxide, Pb3O4. Lead monoxide exists in two modifications, litharge and massicot. Litharge, or alpha lead monoxide, is a red or reddish yellow solid, has a tetragonal crystal structure, and is the stable form at temperatures below 488 °C (910 °F). Massicot, or beta lead monoxide, is a yellow solid and has an orthorhombic crystal structure; it is the stable form above 488 °C. Both forms are insoluble in water but dissolve in acids to form salts containing the Pb2+ ion or in alkalies to form plumbites, which have the PbO22− ion. Litharge, which is produced by air oxidation of lead, is the most important commercial compound of lead; it is used in large amounts directly and as the starting material for the preparation of other lead compounds. Considerable quantities of PbO are consumed in manufacturing the plates of lead-acid storage batteries. High-quality glassware (lead crystal) contains as much as 30 percent litharge, which increases the refractive index of the glass and makes it brilliant, strong, and resonant. Litharge is also employed as a drier in varnishes and in making sodium plumbite, which is used for removing malodorous thiols (a family of organic compounds containing sulfur) from gasoline.

PbO2, found in nature as the brown-to-black mineral plattnerite, is commercially produced from trilead tetroxide by oxidation with chlorine. It decomposes upon heating and yields oxygen and lower oxides of lead. PbO2 is used as an oxidizing agent in the production of dyestuffs, chemicals, pyrotechnics, and matches and as a curing agent for polysulfide rubbers. Trilead tetroxide (known as red lead, or minium) is produced by further oxidation of PbO. It is the orange-red to brick-red pigment commonly used in corrosion-resistant paints for exposed iron and steel. It also reacts with ferric oxide to form a ferrite used in making permanent magnets.

Another economically significant compound of lead in the +2 oxidation state is lead acetate, Pb(C2H3O2)2, a water-soluble salt made by dissolving litharge in concentrated acetic acid. The common form, the trihydrate, Pb(C2H3O2)2·3H2O, called sugar of lead, is used as a mordant in dyeing and as a drier in certain paints. In addition, it is utilized in the production of other lead compounds and in gold cyanidation plants, where it primarily serves to precipitate soluble sulfides from solution as PbS.

Various other salts, most notably basic lead carbonate, basic lead sulfate, and basic lead silicate, were once widely employed as pigments for white exterior paints. Since the mid-20th century, however, the use of such so-called white lead pigments has decreased substantially because of a concern over their toxicity and attendant hazard to human health. The use of lead math in insecticides has virtually been eliminated for the same reason.

More Information:

Appearance

A dull, silvery-grey metal. It is soft and easily worked into sheets.

Uses

This easily worked and corrosion-resistant metal has been used for pipes, pewter and paint since Roman times. It has also been used in lead glazes for pottery and, in this century, insecticides, hair dyes and as an anti-knocking additive for petrol. All these uses have now been banned, replaced or discouraged as lead is known to be detrimental to health, particularly that of children.

Lead is still widely used for car batteries, pigments, ammunition, cable sheathing, weights for lifting, weight belts for diving, lead crystal glass, radiation protection and in some solders.

It is often used to store corrosive liquids. It is also sometimes used in architecture, for roofing and in stained glass windows.

Biological role

Lead has no known biological role. It can accumulate in the body and cause serious health problems. It is toxic, teratogenic (disturbs the development of an embryo or foetus) and carcinogenic.

Daily intake of lead from all sources is about 0.1 milligrams. The average human body stores about 120 milligrams of lead in the bones.

Natural abundance

Lead is chiefly obtained from the mineral galena by a roasting process. At least 40% of lead in the UK is recycled from secondary sources such as scrap batteries and pipes.

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Lead

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