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Lettris is a curious tetris-clone game where all the bricks have the same square shape but different content. Each square carries a letter. To make squares disappear and save space for other squares you have to assemble English words (left, right, up, down) from the falling squares.
Boggle gives you 3 minutes to find as many words (3 letters or more) as you can in a grid of 16 letters. You can also try the grid of 16 letters. Letters must be adjacent and longer words score better. See if you can get into the grid Hall of Fame !
Change the target language to find translations.
Tips: browse the semantic fields (see From ideas to words) in two languages to learn more.
1.a soft heavy toxic malleable metallic element; bluish white when freshly cut but tarnishes readily to dull grey"the children were playing with lead soldiers"
2.the playing of a card to start a trick in bridge"the lead was in the dummy"
3.a position of leadership (especially in the phrase `take the lead')"he takes the lead in any group" "we were just waiting for someone to take the lead" "they didn't follow our lead"
4.a jumper that consists of a short piece of wire"it was a tangle of jumper cables and clip leads"
5.mixture of graphite with clay in different degrees of hardness; the marking substance in a pencil
6.thin strip of metal used to separate lines of type in printing
7.restraint consisting of a rope (or light chain) used to restrain an animal
8.the timing of ignition relative to the position of the piston in an internal-combustion engine
9.an advantage held by a competitor in a race"he took the lead at the last turn"
10.(game) a player's turn to take some action permitted by the rules of the game
11.evidence pointing to a possible solution"the police are following a promising lead" "the trail led straight to the perpetrator"
12.the introductory section of a story"it was an amusing lead-in to a very serious matter"
13.a news story of major importance
14.an indication of potential opportunity"he got a tip on the stock market" "a good lead for a job"
15.(baseball) the position taken by a base runner preparing to advance to the next base"he took a long lead off first"
16.an actor who plays a principal role
17.the angle between the direction a gun is aimed and the position of a moving target (correcting for the flight time of the missile)
18.(sports) the score by which a team or individual is winning
19.(ellipsis)the advantage gained by beginning early (as in a race)"with an hour's start he will be hard to catch"
1.cause to undertake a certain action"Her greed led her to forge the checks"
2.preside over"John moderated the discussion"
3.lead, as in the performance of a composition"conduct an orchestra; Barenboim conducted the Chicago symphony for years"
4.move ahead (of others) in time or space
5.travel in front of; go in advance of others"The procession was headed by John"
6.take somebody somewhere"We lead him to our chief" "can you take me to the main entrance?" "He conducted us to the palace"
7.be in charge of"Who is heading this project?"
8.be conducive to"The use of computers in the classroom lead to better writing"
9.have as a result or residue"The water left a mark on the silk dress" "Her blood left a stain on the napkin"
10.tend to or result in"This remark lead to further arguments among the guests"
11.stretch out over a distance, space, time, or scope; run or extend between two points or beyond a certain point"Service runs all the way to Cranbury" "His knowledge doesn't go very far" "My memory extends back to my fourth year of life" "The facts extend beyond a consideration of her personal assets"
12.lead, extend, or afford access"This door goes to the basement" "The road runs South"
13.cause something to pass or lead somewhere"Run the wire behind the cabinet"
14.be ahead of others; be the first"she topped her class every year"
15.pass or spend"lead a good life"
1.(MeSH)A soft, grayish metal with poisonous salts; atomic number 82, atomic weight 207.19, symbol Pb. (Dorland, 28th)
LeadLead (lĕd), n. [OE. led, leed, lead, AS. leád; akin to D. lood, MHG. lōt, G. loth plummet, sounding lead, small weight, Sw. & Dan. lod. √123.]
1. (Chem.) One of the elements, a heavy, pliable, inelastic metal, having a bright, bluish color, but easily tarnished. It is both malleable and ductile, though with little tenacity, and is used for tubes, sheets, bullets, etc. Its specific gravity is 11.37. It is easily fusible (melting point 327.5° C), forms alloys with other metals, and is an ingredient of solder and type metal. Atomic number 82. Atomic weight, 207.2. Symbol Pb (L. Plumbum). It is chiefly obtained from the mineral galena, lead sulphide.
2. An article made of lead or an alloy of lead; as: (a) A plummet or mass of lead, used in sounding at sea. (b) (Print.) A thin strip of type metal, used to separate lines of type in printing. (c) Sheets or plates of lead used as a covering for roofs; hence, pl., a roof covered with lead sheets or terne plates.
I would have the tower two stories, and goodly leads upon the top. Bacon
3. A small cylinder of black lead or graphite, used in pencils.
Black lead, graphite or plumbago; -- so called from its leadlike appearance and streak. [Colloq.] -- Coasting lead, a sounding lead intermediate in weight between a hand lead and deep-sea lead. -- Deep-sea lead, the heaviest of sounding leads, used in water exceeding a hundred fathoms in depth. Ham. Nav. Encyc. -- Hand lead, a small lead use for sounding in shallow water. -- Krems lead, Kremnitz lead [so called from Krems or Kremnitz, in Austria], a pure variety of white lead, formed into tablets, and called also Krems white, or Kremnitz white, and Vienna white. -- Lead arming, tallow put in the hollow of a sounding lead. See To arm the lead (below). -- Lead colic. See under Colic. -- Lead color, a deep bluish gray color, like tarnished lead. -- Lead glance. (Min.) Same as Galena. -- Lead line (a) (Med.) A dark line along the gums produced by a deposit of metallic lead, due to lead poisoning. (b) (Naut.) A sounding line. -- Lead mill, a leaden polishing wheel, used by lapidaries. -- Lead ocher (Min.), a massive sulphur-yellow oxide of lead. Same as Massicot. -- Lead pencil, a pencil of which the marking material is graphite (black lead). -- Lead plant (Bot.), a low leguminous plant, genus Amorpha (Amorpha canescens), found in the Northwestern United States, where its presence is supposed to indicate lead ore. Gray. -- Lead tree. (a) (Bot.) A West Indian name for the tropical, leguminous tree, Leucæna glauca; -- probably so called from the glaucous color of the foliage. (b) (Chem.) Lead crystallized in arborescent forms from a solution of some lead salt, as by suspending a strip of zinc in lead acetate. -- Mock lead, a miner's term for blende. -- Red lead, a scarlet, crystalline, granular powder, consisting of minium when pure, but commonly containing several of the oxides of lead. It is used as a paint or cement and also as an ingredient of flint glass. -- Red lead ore (Min.), crocoite. -- Sugar of lead, acetate of lead. -- To arm the lead, to fill the hollow in the bottom of a sounding lead with tallow in order to discover the nature of the bottom by the substances adhering. Ham. Nav. Encyc. -- To cast the lead, or To heave the lead, to cast the sounding lead for ascertaining the depth of water. -- White lead, hydrated carbonate of lead, obtained as a white, amorphous powder, and much used as an ingredient of white paint.
LeadLead (lĕd), v. t. [imp. & p. p. Leaded; p. pr. & vb. n. Leading.]
1. To cover, fill, or affect with lead; as, continuous firing leads the grooves of a rifle.
2. (Print.) To place leads between the lines of; as, to lead a page; leaded matter.
LeadLead (lēd), v. t. [imp. & p. p. Led (lĕd); p. pr. & vb. n. Leading.] [OE. leden, AS. lǣdan (akin to OS. lēdian, D. leiden, G. leiten, Icel. leīða, Sw. leda, Dan. lede), properly a causative fr. AS. liðan to go; akin to OHG. līdan, Icel. līða, Goth. leiþan (in comp.). Cf. Lode, Loath.]
1. To guide or conduct with the hand, or by means of some physical contact or connection; as, a father leads a child; a jockey leads a horse with a halter; a dog leads a blind man.
If a blind man lead a blind man, both fall down in the ditch. Wyclif (Matt. xv. 14.)
They thrust him out of the city, and led him unto the brow of the hill. Luke iv. 29.
In thy right hand lead with thee
The mountain nymph, sweet Liberty. Milton.
2. To guide or conduct in a certain course, or to a certain place or end, by making the way known; to show the way, esp. by going with or going in advance of. Hence, figuratively: To direct; to counsel; to instruct; as, to lead a traveler; to lead a pupil.
The Lord went before them by day in a pillar of a cloud, to lead them the way. Ex. xiii. 21.
He leadeth me beside the still waters. Ps. xxiii. 2.
This thought might lead me through the world's vain mask.
Content, though blind, had I no better guide. Milton.
3. To conduct or direct with authority; to have direction or charge of; as, to lead an army, an exploring party, or a search; to lead a political party.
Christ took not upon him flesh and blood that he might conquer and rule nations, lead armies, or possess places. South.
4. To go or to be in advance of; to precede; hence, to be foremost or chief among; as, the big sloop led the fleet of yachts; the Guards led the attack; Demosthenes leads the orators of all ages.
As Hesperus, that leads the sun his way. Fairfax.
And lo ! Ben Adhem's name led all the rest. Leigh Hunt.
5. To draw or direct by influence, whether good or bad; to prevail on; to induce; to entice; to allure; as, to lead one to espouse a righteous cause.
He was driven by the necessities of the times, more than led by his own disposition, to any rigor of actions. Eikon Basilike.
Silly women, laden with sins, led away by divers lusts. 2 Tim. iii. 6 (Rev. Ver.).
6. To guide or conduct one's self in, through, or along (a certain course); hence, to proceed in the way of; to follow the path or course of; to pass; to spend. Also, to cause (one) to proceed or follow in (a certain course).
That we may lead a quiet and peaceable life. 1 Tim. ii. 2.
Nor thou with shadowed hint confuse
A life that leads melodious days. Tennyson.
You remember . . . the life he used to lead his wife and daughter. Dickens.
7. (Cards & Dominoes) To begin a game, round, or trick, with; as, to lead trumps; the double five was led.
To lead astray, to guide in a wrong way, or into error; to seduce from truth or rectitude. -- To lead captive, to carry or bring into captivity. -- To lead the way, to show the way by going in front; to act as guide. Goldsmith.
LeadLead (?), v. i.
1. To guide or conduct, as by accompanying, going before, showing, influencing, directing with authority, etc.; to have precedence or preëminence; to be first or chief; -- used in most of the senses of lead, v. t.
2. To tend or reach in a certain direction, or to a certain place; as, the path leads to the mill; gambling leads to other vices.
The mountain foot that leads towards Mantua. Shak.
To lead off or To lead out, to go first; to begin; as, Mickey Mantle led off in the fifth inning of the game.
1. The act of leading or conducting; guidance; direction; as, to take the lead; to be under the lead of another.
At the time I speak of, and having a momentary lead, . . . I am sure I did my country important service. Burke.
2. Precedence; advance position; also, the measure of precedence; as, the white horse had the lead; a lead of a boat's length, or of half a second.
3. (Cards & Dominoes) The act or right of playing first in a game or round; the card suit, or piece, so played; as, your partner has the lead.
4. An open way in an ice field. Kane.
5. (Mining) A lode.
6. (Naut.) The course of a rope from end to end.
7. (Steam Engine) The width of port opening which is uncovered by the valve, for the admission or release of steam, at the instant when the piston is at end of its stroke.
☞ When used alone it means outside lead, or lead for the admission of steam. Inside lead refers to the release or exhaust.
8. (Civil Engineering) the distance of haul, as from a cutting to an embankment.
9. (Horology) The action of a tooth, as a tooth of a wheel, in impelling another tooth or a pallet. Saunier.
10. (Music.) (a) The announcement by one voice part of a theme to be repeated by the other parts. (b) A mark or a short passage in one voice part, as of a canon, serving as a cue for the entrance of others.
11. In an internal-combustion engine, the distance, measured in actual length of piston stroke or the corresponding angular displacement of the crank, of the piston from the end of the compression stroke when ignition takes place; -- called in full lead of the ignition. When ignition takes place during the working stroke the corresponding distance from the commencement of the stroke is called negative lead.
12. (Mach.) The excess above a right angle in the angle between two consecutive cranks, as of a compound engine, on the same shaft.
13. (Mach.) In spiral screw threads, worm wheels, or the like, the amount of advance of any point in the spiral for a complete turn.
14. (Elec.) (a) The angle between the line joining the brushes of a continuous-current dynamo and the diameter symmetrical between the poles. (b) The advance of the current phase in an alternating circuit beyond that of the electromotive force producing it.
15. (Theat.) A role for a leading man or leading woman; also, one who plays such a role.
16. The first story in a newspaper or broadcast news program.
17. an electrical conductor, typically as an insulated wire or cable, connecting an electrical device to another device or to a power source, such as a conductor conveying electricity from a dynamo.
18. (Baseball) the distance a runner on base advances from one base toward the next before the pitch; as, the long lead he usually takes tends to distract the pitchers.
Lead angle (Steam Engine), the angle which the crank maker with the line of centers, in approaching it, at the instant when the valve opens to admit steam. -- Lead screw (Mach.), the main longitudinal screw of a lathe, which gives the feed motion to the carriage.
atomic number 82, booster cable, clue, confidential information, cue, electric cord, flex, guide, head start, hint, indication, inkling, intimation, jumper cable, jumper lead, lead-in, leading, lead story, leash, lede, move, package pin, Pb, pencil lead, pointer, precedence, principal, spark advance, star, steer, suggestion, tether, tip, track, trail, vanguard, wind, pin (ellipsis)
Burton's lead line • CF lead • CR lead • Ditiocarb, Lead Salt • Lead Encephalopathy, Childhood • Lead Induced Nervous System Diseases, Adult • Lead Poisoning • Lead Poisoning, Nervous System • Lead Poisoning, Nervous System, Adult • Lead Poisoning, Nervous System, Childhood • Lead Poisoning, Neurologic • Lead Poisoning, Neurologic, Adult • Lead Poisoning, Neurologic, Childhood • Lead Polyneuropathy • Lead Radioisotopes • Lead and its compounds • Lead-Induced Nervous System Disease, Childhood • Lead-Induced Nervous System Diseases • Lead-Induced Polyneuropathy • Lead-induced gout • Lead-induced gout | ankle and foot • Lead-induced gout | forearm • Lead-induced gout | hand • Lead-induced gout | lower leg • Lead-induced gout | multiple sites • Lead-induced gout | other • Lead-induced gout | pelvic region and thigh • Lead-induced gout | shoulder region • Lead-induced gout | site unspecified • Lead-induced gout | upper arm • Nervous System Disease, Lead-Induced, Childhood • Nervous System Diseases, Lead Induced, Adult • Nervous System Diseases, Lead-Induced • Nervous System Poisoning, Lead • Nervous System Poisoning, Lead, Adult • Nervous System Poisoning, Lead, Childhood • Nervous System Toxicity, Lead, Adult • Neurotoxicity Syndrome, Lead • Neurotoxicity Syndrome, Lead, Adult • Neurotoxicity Syndrome, Lead, Childhood • Poisoning, Lead • Poisoning, Lead, Nervous System • Poisoning, Lead, Nervous System, Adult • Poisoning, Lead, Nervous System, Childhood • Poisoning, Lead, Neurologic • Poisoning, Lead, Neurologic, Adult • Poisoning, Lead, Neurologic, Childhood • Polyneuropathy, Lead-Induced • Tetraethyl Lead • acetate of lead • all roads lead to Rome • antimonial lead • antimony-lead alloy • be in the lead • black lead • black lead pencil • clip lead • extension lead • female lead • galena lead sulphide • green lead ore • hard lead • in the lead • jump lead • jumper lead • lead I • lead a vegetable life • lead a vegetative life • lead acetate • lead alloy cooled fast reactor • lead angle • lead arsenate • lead astray • lead away • lead bank • lead bronze • lead by the nose • lead carbonate • lead chromate • lead colic • lead cooled fast reactor • lead glance • lead glass • lead in • lead into temptation • lead line • lead off • lead on • lead ore • lead pencil • lead plant • lead poisoning • lead sheet • lead story • lead sulfide • lead tetraethyl • lead the way • lead time • lead to • lead to nothing • lead tree • lead up • lead up the garden path • lead up to • lead-acid accumulator • lead-acid battery • lead-colored • lead-coloured • lead-free • lead-free gasoline • lead-free petrol • lead-glass • lead-in • made of lead • male lead • natural lead sulphide • no-lead gasoline • of lead • pencil lead • pig lead • red lead • red-lead putty • sounding lead • sugar of lead • tetra-ethyl lead • tetraethyl lead • the lead • white lead • white lead ore
|Name, symbol, number||lead, Pb, 82|
|Element category||post-transition metal|
|Group, period, block||14, 6, p|
|Standard atomic weight||207.2|
|Electron configuration||[Xe] 4f14 5d10 6s2 6p2|
|Electrons per shell||2, 8, 18, 32, 18, 4 (Image)|
|Density (near r.t.)||11.34 g·cm−3|
|Liquid density at m.p.||10.66 g·cm−3|
|Melting point||600.61 K, 327.46 °C, 621.43 °F|
|Boiling point||2022 K, 1749 °C, 3180 °F|
|Heat of fusion||4.77 kJ·mol−1|
|Heat of vaporization||179.5 kJ·mol−1|
|Molar heat capacity||26.650 J·mol−1·K−1|
|Oxidation states||4, 2 (Amphoteric oxide)|
|Electronegativity||2.33 (Pauling scale)|
|Ionization energies||1st: 715.6 kJ·mol−1|
|2nd: 1450.5 kJ·mol−1|
|3rd: 3081.5 kJ·mol−1|
|Atomic radius||175 pm|
|Covalent radius||146±5 pm|
|Van der Waals radius||202 pm|
|Crystal structure||face-centered cubic|
|Electrical resistivity||(20 °C) 208 nΩ·m|
|Thermal conductivity||35.3 W·m−1·K−1|
|Thermal expansion||(25 °C) 28.9 µm·m−1·K−1|
|Speed of sound (thin rod)||(r.t.) (annealed)
|Young's modulus||16 GPa|
|Shear modulus||5.6 GPa|
|Bulk modulus||46 GPa|
|Brinell hardness||38.3 MPa|
|CAS registry number||7439-92-1|
|Most stable isotopes|
|Main article: Isotopes of lead|
Lead ( //) is a main-group element in the carbon group with the symbol Pb (from Latin: plumbum) and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed to air. Lead has a shiny chrome-silver luster when it is melted into a liquid.
Lead is used in building construction, lead-acid batteries, bullets and shots, weights, as part of solders, pewters, fusible alloys and as a radiation shield. Lead has the highest atomic number of all of the stable elements, although the next higher element, bismuth, has a half-life that is so long (much longer than the age of the universe) that it can be considered stable. Its four stable isotopes have 82 protons, a magic number in the nuclear shell model of atomic nuclei.
Lead, at certain exposure levels, is a poisonous substance to animals as well as for human beings. It damages the nervous system and causes brain disorders. Excessive lead also causes blood disorders in mammals. Like the element mercury, another heavy metal, lead is a neurotoxin that accumulates both in soft tissues and the bones. Lead poisoning has been documented from ancient Rome, ancient Greece, and ancient China.
Lead is a bright and silvery (with a very slight shade of blue) metal in a dry atmosphere; upon contact with air, it begins to tarnish. It has a few characteristic properties: high density, softness, ductility and malleability, poor electrical conductivity (compared to other metals), high resistance to corrosion, and ability to react with organic chemicals.
Various traces of other metals change its properties significantly: addition of small amounts of antimony or copper increases hardness and improves the corrosion reflection from sulfuric acid for lead. A few other metals also improve only hardness and fight the metal fatigue, such as cadmium, tin, or tellurium; metals like sodium or calcium also have this ability, but they weaken the chemical stability. Finally, zinc and bismuth simply impair the corrosion resistance (0.1% bismuth content prevent lead from the industrial usage). In return, lead impurities mostly worsen the quality of industrial materials, although there are exceptions: for example, small amounts of lead improve the ductility of steel.
Lead has only one common allotrope, which is face-centered cubic, with the lead–lead distance being 349 pm. At 327.5 °C (621.5 °F), lead melts; the melting point is above that of tin (232 °C, 449.5 °F), but significantly below that of germanium (938 °C, 1721 °F). The boiling point of lead is 1749 °C (3180 °F), which is below than those of both tin (2602 °C, 4716 °F) and germanium (2833 °C, 5131 °F). Densities get simply bigger down the group: the Ge and Sn values (5.23 and 7.29 g·cm−3, respectively) are significantly below that of lead: 11.32 g·cm−3.
A lead atom has 82 electrons, having an electronic configuration of [Xe]4f145d106s26p2. In its compounds, lead (unlike the other group 14 elements) most commonly loses its two and not four outermost electrons, becoming lead(II) ions, Pb2+. Such unusual behavior is rationalized by considering the inert pair effect, which occurs because of the stabilization of 6s-orbital due to relativistic effects, which are stronger closer to the bottom of the periodic table. Tin shows a weaker such effect: tin(II) is still a reducer.
The figures for electrode potential show that lead is only slightly easier to oxidize than hydrogen. Lead thus can dissolve in acids, but this is often impossible due to specific problems (such as insoluble salts formation). Powdered lead burns with a bluish-white flame. As with many metals, finely divided powdered lead exhibits pyrophoricity. Toxic fumes are released when lead is burned.
Lead occurs naturally on Earth exclusively in the form of four isotopes: lead-204, -206, -207, and -208. All four can be radioactive as the hypothetical alpha decay of any would release energy, but the lower half-life limit has been put only for lead-204: over 1.4×1017 years. This effect is, however, so weak that natural lead makes no radiation hazard. Three of them are also found in three of the four major decay chains: lead-206, -207 and -208 are final decay products of uranium-238, uranium-235, and thorium-232, respectively. Since the amounts of them in nature depend also on other elements' presence, the isotopic composition of natural lead varies by sample: in particular, the relative amount of lead-206 varies between 20.84% and 27.78%.
Aside from the stable ones, thirty-four radioisotopes have been synthesized: they have the mass numbers of 178–215. Lead-205 is the most stable radioisotope of lead, with a half-life of over 107 years. 47 nuclear isomers (long-lived excited nuclear states), corresponding to 24 lead isotopes, have been characterized. The most long-lived isomer is lead-204m2 (half-life of about 1.1 hours).
Lead is classified as a post-transition metal, being a member of group 14 of the periodic table. Lead only form a protective oxide layer although finely powdered highly purified lead could ignite in the air. Melted lead is oxidized in air to lead monoxide. All chalcogens oxidize lead upon heating.
Fluorine does not oxidize cold lead. Hot lead can be oxidized, but the formation of a protective halide layer lowers the intensity of the reaction above 100 °C (210 °F). The reaction with chlorine is similar: thanks to the chloride layer, lead persistence against chlorine surpasses those of copper or steel up to 300 °C (570 °F).
Water in presence of oxygen attacks lead to start an accelerating reaction. Presence of carbonates or sulfates lead to formation of insoluble lead salts, which prevent the metal from corrosion. So does carbon dioxide, as the insoluble lead carbonate is formed; however, excess of the gas leads to the formation of the soluble bicarbonate; this dangers the usage of lead pipes. Lead dissolves in organic acids (in presence of oxygen) and concentrated (≥80%) sulfuric acid thanks to complexation; however, it is only weakly affected by hydrochloric acid and is stable against hydrofluoric acid, as the corresponding halides are weakly soluble. Lead also dissolves in quite concentrated alkalis (≥10%) thanks to the amphoteric character and solubility of plumbites.
Lead compounds exist mainly in two main oxidation states, +2 and +4. The former is more common. Inorganic lead(IV) compounds are typically strong oxidants or exist only in highly acidic solutions.
Three oxides are known: PbO, Pb3O4 (sometimes called "minium"), and PbO2. The monoxide exists as two allotropes: α-PbO and β-PbO, both with layer structure and tetracoordinated lead. The alpha polymorph is red-colored and has the Pb–O distance of 230 pm; the beta polymorph is yellow-colored and has the Pb–O distance of 221 and 249 pm (due to asymmetry). Both polymorphs can exist under standard conditions (beta with small (10−5 relative) impurities, such as Si, Ge, Mo, etc.). PbO reacts with acids to form salts, and with alkalies to give plumbites, [Pb(OH)3]- or [Pb(OH)4]2-. The monoxide oxidizes in air to trilead tetroxide, which at 550 °C (1020 °F) degrades back into PbO.
The dioxide may be prepared by, for example, halogenization of lead(II) salts. Regardless the polymorph, it has a black-brown color. The alpha allotrope is rhombohedral, and the beta allotrope is tetragonal. Both allotropes are black-brown in color and always contain some water, which cannot be removed, as heating also causes decomposition (to PbO and Pb3O4). The dioxide is a powerful oxidizer: it can oxidize hydrochloric and sulfuric acids. It does not reacts with alkaline solution, but reacts with solid alkalies to give hydroxyplumbates, or with basic oxides to give plumbates.
Reaction of lead salts with hydrogen sulfide yields lead sulfide. The solid has the NaCl-like striucture (simple cubic), which it keeps up to the melting point, 1114 °C (2037 °F). When heated in air, it oxidised to the sulfate and then the monoxide. The compounds is almost insoluble in water, weak acids, and (NH4)2S/(NH4)2S2 solution is the key for separation of lead from analythical groups I to III elements, tin, arsenic, and antimony. The compounds, however, dissolves in nitric and hydrochloric acids, to give elemental sulfur and hydrogen sulfide, respectively. Heating a mixture of the monoxide and the sulfide heated together forms the metal.
Heating lead carbonate with hydrogen fluoride yields the hydrofluoride, which decomposes to the difluoride when melts. This white crystalline powder is more soluble than the diiodide, but less than the dibromide and the dichloride. The tetrafluoride, a yellow crystalline powder, is unstable.
Other dihalides are obtained upon heating lead(II) salts with the halides of other metals; lead dihalides precipitate to give white orthorhombic crystals (diiodide forms yellow hexagonal crystals). They can also be obtained by direct elements reaction at temperature exceeding melting points of dihalides. Their solubility increases with temperature; adding more halides first decreases the solubility, but then increases due to complexation, with the maximum coordination number being 6. The complexation depends on halide ion numbers, atomic number of the alkali metal, the halide of which is added, temperature and solution ionic strength. The tetrachloride is obtained upon dissolving the dioxide in hydrochloric acid; to prevent the exothermic decomposition, it is kept under concentrated sulfuric acid. The tetrabromide may not, and the tetraiodide definitely does not exist. The diastatide has also been prepared.
The metal is not attacked by sulfuric or hydrochloric acids. It dissolves in nitric acid with the evolution of nitric oxide gas to form dissolved Pb(NO3)2. It is a well-soluble solid in water; it is thus a key to receive the precipitates of halides, sulfate, chromate, carbonate, and basic carbonate Pb3(OH)2(CO3)2 salts of lead.
The best-known compounds are the two simplest plumbane deratives: tetramethyllead (TML) and tetraethyllead (TEL). The homologs of these, as well as hexaethyldilead (HEDL), are of lesser stability. The tetralkyl deratives contain lead(IV); the Pb–C bonds are covalent. They thus resemble typical organic compounds.
Lead readily forms an equimolar alloy with sodium metal that reacts with alkyl halides to form organometallic compounds of lead such as tetraethyllead. The Pb–C bond energies in TML and TEL are only 167 and 145 kJ/mol; the compounds thus decompose upon heating, with first signs of TEL composition seen at 100 °C (210 °F). The pyrolisis yields of elemental lead and alkyl radicals; their interreaction causes the synthesis of HEDL. TML and TEL also decompose upon sunlight or UV light. In presence of chlorine, the alkyls begin to be replaced with chlorides; the R2PbCl2 in the presence of HCl (a by-product of the previous reaction) leads to the complete mineralization to give PbCl2. Reaction with bromine follows the same principle.
Lead has been commonly used for thousands of years because it is widespread, easy to extract and easy to work with. It is highly malleable and ductile as well as easy to smelt. Metallic lead beads dating back to 6400 BCE have been found in Çatalhöyük in modern-day Turkey. In the early Bronze Age, lead was used with antimony and arsenic.
The largest preindustrial producer of lead was the Roman economy, with an estimated output per annum of 80,000 t, which was typically won as a by-product of extensive silver smelting. Roman mining activities occurred in Central Europe, Roman Britain, the Balkans, Greece, Asia Minor; Hispania alone accounted for 40% of world production.
Roman lead pipes often bore the insignia of Roman emperors (see Roman lead pipe inscriptions). Lead plumbing in the Latin West may have been continued beyond the age of Theoderic the Great into the medieval period. Many Roman "pigs" (ingots) of lead figure in Derbyshire lead mining history and in the history of the industry in other English centers. The Romans also used lead in molten form to secure iron pins that held together large limestone blocks in certain monumental buildings. In alchemy, lead was thought to be the oldest metal and was associated with the planet Saturn. Alchemists accordingly used Saturn's symbol (the scythe, ♄) to refer to lead.
Up to the 17th century, tin was often not differed from lead: lead was called plumbum nigrum (literally, "black plumbum"), while tin was called plumbum candidum (literally, "bright plumbum"). Their inherence through history can be seen in other languages: the word "olovo" stands for lead in Czech, but in Russian it ("олово") stands for tin. Lead's symbol Pb is an abbreviation of its Latin name plumbum for soft metals; the English words "plumbing", "plumber", "plumb", and "plumb-bob" also derive from this Latin root.
Metallic lead does occur in nature, but it is rare. Lead is usually found in ore with zinc, silver and (most abundantly) copper, and is extracted together with these metals. The main lead mineral is galena (PbS), which contains 86.6 % lead by weight. Other common varieties are cerussite (PbCO3) and anglesite (PbSO4).
Most ores contain less than 10% lead, and ores containing as little as 3% lead can be economically exploited. Ores are crushed and concentrated by froth flotation typically to 70% or more. Sulfide ores are roasted, producing primarily lead oxide and a mixture of sulfates and silicates of lead and other metals contained in the ore.
Lead oxide from the roasting process is reduced in a coke-fired blast furnace to the metal. Additional layers separate in the process and float to the top of the metallic lead. These are slag (silicates containing 1.5% lead), matte (sulfides containing 15% lead), and speiss (arsenides of iron and copper). These wastes contain concentrations of copper, zinc, cadmium, and bismuth that can be recovered economically, as can their content of unreduced lead.
Metallic lead that results from the roasting and blast furnace processes still contains significant contaminants of arsenic, antimony, bismuth, zinc, copper, silver, and gold. The melt is treated in a reverberatory furnace with air, steam, and sulfur, which oxidizes the contaminants except silver, gold, and bismuth. The oxidized contaminants are removed by drossing, where they float to the top and are skimmed off.
Since lead ores contain significant concentrations of silver, the smelted metal also is commonly contaminated with silver. Metallic silver as well as gold is removed and recovered economically by means of the Parkes process.
Very pure lead can be obtained by processing smelted lead electrolytically by means of the Betts process. The process uses anodes of impure lead and cathodes of pure lead in an electrolyte of silica fluoride.
Production and consumption of lead is increasing worldwide. Total annual production is about 8 million tonnes; about half is produced from recycled scrap. The top lead producing countries, as of 2008, are Australia, China, USA, Peru, Canada, Mexico, Sweden, Morocco, South Africa and North Korea. Australia, China and the United States account for more than half of primary production.
At current use rates, the supply of lead is estimated to run out in 42 years. Environmental analyst Lester Brown has suggested lead could run out within 18 years based on an extrapolation of 2% growth per year. This may need to be reviewed to take account of renewed interest in recycling, and rapid progress in fuel cell technology. According to the International Resource Panel's Metal Stocks in Society report, the global per capita stock of lead in use in society is 8 kg. Much of this is in more-developed countries (20–150 kg per capita) rather than less-developed countries (1–4 kg per capita).
Because of its high density and resistance from corrosion, lead is used for the ballast keel of sailboats. Its high density allows it to counterbalance the heeling effect of wind on the sails while at the same time occupying a small volume and thus offering the least underwater resistance. For the same reason it is used in scuba diving weight belts to counteract the diver's natural buoyancy and that of his equipment. It does not have the weight-to-volume ratio of many heavy metals, but its low cost increases its use in these and other applications.
Lead is used in applications where its low melting point, ductility and high density is an advantage. The low melting point makes casting of lead easy, and therefore small arms ammunition and shotgun pellets can be cast with minimal technical equipment. It is also inexpensive and denser than other common metals. The hot metal typesetting uses a lead based alloy to produce the types for printing directly before printing.
Its corrosion resistance makes it suitable for outdoor applications when in contact with water.
Lead is used as electrodes in the process of electrolysis. Lead is used in solder for electronics, although this usage is being phased out by some countries to reduce the amount of environmentally hazardous waste. Lead is used in high voltage power cables as sheathing material to prevent water diffusion into insulation.
Lead is one of three metals used in the Oddy test for museum materials, helping detect organic acids, aldehydes, and acidic gases.
Lead is added to brass to reduce machine tool wear. Lead, in the form of strips, or tape, is used for the customization of tennis rackets. Tennis rackets of the past sometimes had lead added to them by the manufacturer to increase weight.
Lead is used to form glazing bars for stained glass or other multi-lit windows. The practice has become less common, not for danger but for stylistic reasons. Lead, or sheet-lead, is used as a sound deadening layer in some areas in wall, floor and ceiling design in sound studios where levels of airborne and mechanically produced sound are targeted for reduction or virtual elimination.
Lead has many uses in the construction industry (e.g., lead sheets are used as architectural metals in roofing material, cladding, flashing, gutters and gutter joints, and on roof parapets). Detailed lead moldings are used as decorative motifs used to fix lead sheet. Lead is still widely used in statues and sculptures. Lead is often used to balance the wheels of a car; this use is being phased out in favor of other materials for environmental reasons.
Lead compounds are used as a coloring element in ceramic glazes, notably in the colors red and yellow. Lead is frequently used in polyvinyl chloride (PVC) plastic, which coats electrical cords.
Lead is used in some candles to treat the wick to ensure a longer, more even burn. Because of the dangers, European and North American manufacturers use more expensive alternatives such as zinc. Lead glass is composed of 12–28% lead oxide. It changes the optical characteristics of the glass and reduces the transmission of radiation.
Some artists using oil-based paints continue to use lead carbonate white, citing its properties in comparison with the alternatives. Tetra-ethyl lead is used as an anti-knock additive for aviation fuel in piston-driven aircraft. Lead-based semiconductors, such as lead telluride, lead selenide and lead antimonide are finding applications in photovoltaic (solar energy) cells and infrared detectors.
Lead pigments were used in lead paint for white as well as yellow, orange, and red. Most uses have been discontinued due of the dangers of lead poisoning. Beginning April 22, 2010, US federal law requires that contractors performing renovation, repair, and painting projects that disturb more than six square feet of paint in homes, child care facilities, and schools built before 1978 must be certified and trained to follow specific work practices to prevent lead contamination. Lead chromate is still in industrial use. Lead carbonate (white) is the traditional pigment for the priming medium for oil painting, but it has been largely displaced by the zinc and titanium oxide pigments. It was also quickly replaced in water-based painting mediums. Lead carbonate white was used by the Japanese geisha and in the West for face-whitening make-up, which was detrimental to health.
Lead is the hot metal that was used in hot metal typesetting. It was used for plumbing (hence the name) as well as a preservative for food and drink in Ancient Rome. Until the early 1970s, lead was used for joining cast iron water pipes and used as a material for small diameter water pipes.
Tetraethyllead was used in leaded fuels to reduce engine knocking, but this practice has been phased out across many countries of the world in efforts to reduce toxic pollution that affected humans and the environment.
Lead was used to make bullets for slings. Lead was used for shotgun pellets in the US until about 1992 when it was outlawed (for waterfowl hunting only) and replaced by non-toxic shot, primarily steel pellets. In the Netherlands, the use of lead shot for hunting and sport shooting was banned in 1993, which caused a large drop in lead emission, from 230 ton in 1990 to 47.5 ton in 1995, two years after the ban.
Lead was a component of the paint used on children's toys – now restricted in the United States and across Europe (ROHS Directive). Lead was used in car body filler, which was used in many custom cars in the 1940s–60s. Hence the term Leadsled. Lead is a superconductor at 7.2 K and IBM tried to make a Josephson effect computer out of lead-alloy.
Lead was also used in pesticides before the 1950s, when fruit orchards were treated (ATSDR). A lead cylinder attached to a long line was used by sailors for the vital navigational task of determining water depth by heaving the lead at regular internals. A soft tallow insert at its base allowed the nature of the sea bed to be determined, further aiding position finding. Contrary to popular belief, pencil leads in wooden pencils have never been made from lead. The term comes from the Roman stylus, called the penicillus, which was made of lead without a wooden holder. When the pencil originated as a wrapped graphite writing tool, the particular type of graphite being used was named plumbago (lit. act for lead, or lead mockup).
Lead is highly poisonous metal (regardless if inhaled or swallowed), affecting almost every organ and system in the body. The main target for lead toxicity is the nervous system, both in adults and children. Long-term exposure of adults can result in decreased performance in some tests that measure functions of the nervous system. Long-term exposure to lead or its salts (especially soluble salts or the strong oxidant PbO2) can cause nephropathy, and colic-like abdominal pains. It may also cause weakness in fingers, wrists, or ankles. Lead exposure also causes small increases in blood pressure, particularly in middle-aged and older people and can cause anemia. Exposure to high lead levels can severely damage the brain and kidneys in adults or children and ultimately cause death. In pregnant women, high levels of exposure to lead may cause miscarriage. Chronic, high-level exposure have shown to reduce fertility in males. Lead also damages nervous connections (especially in young children) and cause blood and brain disorders. Lead poisoning typically results from ingestion of food or water contaminated with lead; but may also occur after accidental ingestion of contaminated soil, dust, or lead-based paint. It is rapidly absorbed into the bloodstream and is believed to have adverse effects on the central nervous system, the cardiovascular system, kidneys, and the immune system. The component limit of lead (1.0 μg/g) is a test benchmark for pharmaceuticals, representing the maximum daily intake an individual should have. However, even at this low level, a prolonged intake can be hazardous to human beings. The treatment for lead poisoning consists of dimercaprol and succimer.
|Fire diamond for lead granules|
The concern about lead's role in cognitive deficits in children has brought about widespread reduction in its use (lead exposure has been linked to learning disabilities). Most cases of adult elevated blood lead levels are workplace-related. High blood levels are associated with delayed puberty in girls. Lead has been shown many times to permanently reduce the cognitive capacity of children at extremely low levels of exposure.
During the 20th century, the use of lead in paint pigments was sharply reduced because of the danger of lead poisoning, especially to children. By the mid-1980s, a significant shift in lead end-use patterns had taken place. Much of this shift was a result of the U.S. lead consumers' compliance with environmental regulations that significantly reduced or eliminated the use of lead in non-battery products, including gasoline, paints, solders, and water systems. Lead use is being further curtailed by the European Union's RoHS directive. Lead may still be found in harmful quantities in stoneware, vinyl (such as that used for tubing and the insulation of electrical cords), and Chinese brass. Older houses may still contain substantial amounts of lead paint. White lead paint has been withdrawn from sale in industrialized countries, but the yellow lead chromate is still in use. Old paint should not be stripped by sanding, as this produces inhalable dust.
Lead salts used in pottery glazes have on occasion caused poisoning, when acidic drinks, such as fruit juices, have leached lead ions out of the glaze. It has been suggested that what was known as "Devon colic" arose from the use of lead-lined presses to extract apple juice in the manufacture of cider. Lead is considered to be particularly harmful for women's ability to reproduce. Lead(II) acetate (also known as sugar of lead) was used by the Roman Empire as a sweetener for wine, and some consider this to be the cause of the dementia that affected many of the Roman Emperors and even be a partial reason for the Roman Empire's fall (see Decline of the Roman Empire#Lead poisoning).
In the human body, lead inhibits porphobilinogen synthase and ferrochelatase, preventing both porphobilinogen formation and the incorporation of iron into protoporphyrin IX, the final step in heme synthesis. This causes ineffective heme synthesis and subsequent microcytic anemia. At lower levels, it acts as a calcium analog, interfering with ion channels during nerve conduction. This is one of the mechanisms by which it interferes with cognition. Acute lead poisoning is treated using disodium calcium edetate: the calcium chelate of the disodium salt of ethylene-diamine-tetracetic acid (EDTA). This chelating agent has a greater affinity for lead than for calcium and so the lead chelate is formed by exchange. This is then excreted in the urine leaving behind harmless calcium.
Exposure to lead and lead chemicals can occur through inhalation, ingestion and dermal contact. Most exposure occurs through ingestion or inhalation; in the U.S. the skin exposure is unlikely as leaded gasoline additives are no longer used. Lead exposure is a global issue as lead mining and lead smelting are common in many countries. Most countries have stopped using lead-containing gasoline by 2007.
Lead exposure mostly occurs through ingestion. Lead paint is the major source of lead exposure for children. As lead paint deteriorates, it peels, is pulverized into dust and then enters the body through hand-to-mouth contact or through contaminated food, water or alcohol. Ingesting certain home remedy medicines may also expose people to lead or lead compounds. Lead can be ingested through fruits and vegetables contaminated by high levels of lead in the soils they were grown in. Soil is contaminated through particulate accumulation from lead in pipes, lead paint and residual emissions from leaded gasoline that was used before the Environment Protection Agency issue the regulation around 1980.
Inhalation is the second major pathway of exposure, especially for workers in lead-related occupations. Almost all inhaled lead is absorbed into the body, the rate is 20–70% for ingested lead; children absorb more than adults.
Dermal exposure may be significant for a narrow category of people working with organic lead compounds, but is of little concern for general population. The rate of skin absorption is also low for inorganic lead.
According to Agency for Toxic Substance and Disease Registry, a small amount of lead (1%) will store itself in bones and the rest will be excreted through urine and feces within a few weeks of exposure. Children have a harder time excreting lead. Only about 32% of lead will be excreted by a child.