200 | The History and Use of Our Earth’s Chemical Elements ExamplesofCompounds
200 | The History and Use of Our Earth’s Chemical Elements ExamplesofCompounds
Germanium monoxide and germanium dioxide are examples of the element’s oxidation states of +2 and +4, as follows: Germanium (II) monoxide: Ge 2+ +O 2- → GeO.
Germanium (IV) dioxide: Ge 4+ + 2O 2- → GeO 2 .
When Germanium dioxide is 99.999% pure, it is used as a semiconductor in transistors, in diodes, and to make special infrared transmitting glass. (The same types of compounds can
be formed with chlorine, and Germanium IV) compounds occur mostly with the sulfide of zinc ore.) Germanium tetrahydride (GeH 4 ) is used to produce crystals of germanium. It is extremely toxic.
Hazards Many of the chemicals used in the semiconductor industries are highly toxic. For example,
germanium-halogen compounds are extremely toxic, both as a powder and in a gaseous state. Precautions should be taken when working with germanium as with similar metalloids from group 14 (IVA).
TIN SYMBOL:Sn PERIOD:5 GROUP:14(IVA) ATOMICNO:50
ATOMICMASS:118.710amu VALENCE:2and4 OXIDATIONSTATE:+2and
+4 NATURALSTATE:Solid ORIGINOFNAME: Thename“tin”isthoughttoberelatedtothepre-RomanEtruscangod Tinia,andthechemicalsymbol(Sn)comesfrom stannum,theLatinwordfortin. ISOTOPES:Thereare49isotopesoftin,10ofwhicharestableandrangefromSn-112
toSn-124.Takentogether,all10stableisotopesmakeupthenaturalabundanceoftin foundonEarth.Theremaining39isotopesareradioactiveandareproducedartificiallyin nuclearreactors.Theirhalf-livesrangefrom190millisecondsto1×10 +5 years.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=18
s2,p6,d10
5-O=4
s2,p2
201 Properties
Guide to the Elements |
Tin is a soft, silvery-white metal located in the carbon group, similar in appearance to fresh- cut aluminum. When polished, it takes on a bluish tint caused by a thin protective coating of oxidized tin. This property makes it useful as a coating for other metals. It is malleable and ductile, meaning it can be pounded, rolled, and formed into many shapes, as well as “pulled” into wires through a die.
There are two allotropes of tin. One is known as gray or alpha (α) tin, which is not very stable. The other is known as white tin or beta (β), which is the most common allotrope. The two forms (allotropes) of tin are dependent on temperature and crystalline structure. White tin is stable at about 13.2°C. Below this temperature, it turns into the unstable gray alpha form. There is also a lesser-known third allotrope of tin called “brittle tin,” which exists above 161°C. Its name is derived from its main property.
Tin’s melting point is 231.93°C, its boiling point is 2,602°C, and the density is 5.75 g/cm 3 for the gray allotrope (alpha) and 7.287 g/cm 3 for the white allotrope (beta).
Characteristics Although tin is located in group 14 as a metalloid, it retains one of the main characteristics
of metals: in reacting with other elements, it gives up electrons, forming positive ions just as do all metals.
Tin has a relatively low melting point (about 231°C or 4,715°F), and it reacts with some acids and strong alkalis, but not with hot water. Its resistance to corrosion is the main charac- teristic that makes it a useful metal.
There is an interesting historical event related to the two main allotropes of tin. At tem- peratures below 13 degrees centigrade, “white” tin is slowly transformed into “gray” tin, which is unstable at low temperatures, and during the brutally cold winter of 1850 in Russia, the tin buttons sewn on soldiers’ uniforms crumbled as the tin changed forms. In the 1800s, tin was also widely used for pots, pans, drinking cups, and dinner flatware. However, at very low temperatures, these implements also disintegrated as their chemical structure was altered.
AbundanceandSource Tin is the 49th most abundant element found in the Earth’s crust. Although tin is not
a rare element, it accounts for about 0.001% of the Earth’s crust. It is found in deposits in Malaysia, Thailand, Indonesia, Bolivia, Congo, Nigeria, and China. Today, most tin is mined as the mineral ore cassiterite (SnO 2 ), also known as tinstone, in Malaysia. Cassiterite is tin’s main ore. There are no significant deposits found in the United States, but small deposits are found on the southeast coast of England. To extract tin from cassiterite, the ore is “roasted” in
a furnace in the presence of carbon, thereby reducing the metal from the slag. History Tin was known and used at least 5,500 years ago, when it was described in the oldest writ-
ten records of the Mediterranean region. It is included in the book of Numbers in the Old Testament, along with the other then-known seven metals (gold, silver, copper, lead, brass, and iron). Bronze is an alloy of 20% tin and 80% melted copper, resulting in a metal that is harder than either pure tin or pure copper. Bronze was an extremely important metal because
202 | The History and Use of Our Earth’s Chemical Elements of its ability to maintain a cutting edge, thus making it suitable for weapons and tools. Before
tin was used to make bronze, early humans used arsenic, which was problematic given that it resulted in death for those working with the toxic element.
Another interesting bit of history regarding tin came around 500 BCE, when the tin mines of the eastern Mediterranean region were depleted. This created a problem because tin, a rather rare metal, was very necessary to make the hardened bronze alloy for weapons and tools. This also is thought to be the first time in human history that a mineral was depleted in a region due to mining.
As the story goes, the Phoenicians set sail westward through the Straits of Gibraltar and dis- covered what were then known as the “tin islands” somewhere in the Atlantic Ocean. Because this was a rich find of an essential metal, they kept the source a secret. It is now believed that they actually found tin on the coast of England in a section we now know as Cornwall, which still produces tin ore.
CommonUses One of the most important uses of tin is in the coating of thin steel sheets to make “tin
plate,” which in turn is used to make what is known as the “tin can.” The tin coating is thin, inexpensive to apply, and resistant to most foods for extended periods of time. Other inert coatings are sometimes used on the inside of the can to further protect the foods for longer periods of time.
Tin is alloyed with many metals. It is added to lead to make low-melting alloys for fire- prevention sprinkler systems and easy-melting solder. It is used for bearings, to plate electrodes, and to make pewter, Babbitt metal, and dental amalgams. Tin also has been mixed with other metals for making castings for letter type used in print- ing presses. Some compounds of tin are used as fungicides and insecticides. Tin is also used for “weight- ing” silk, to give the fabric more body and heft. Molten glass is poured over a pool of molten tin to produce smooth, solid, flat plate and window glass.
ExamplesofCompounds Tin has two oxidation states, +2 and +3. Some examples of tin’s two ions in compounds
follow:
Tin (II) chloride: Sn 2+ + 2 Cl 1- → SnCl 2 (stannous chloride). Tin (IV) chloride: Sn 4+ + 4Cl 1- → SnCl 4 (stannic chloride).
Both of these previous compounds are used as electrolytes in the electrotinning process and as stabilizers in perfumes and soaps. Stannic oxide (SnO 2 ) is a whitish powder used as a ceramic glaze and polishing agent. Stannous fluoride (SnF 2 ) is used as a toothpaste additive to help prevent tooth decay.
Hazards Tin, as the elemental metal, is nontoxic. Most, but not all of tin’s inorganic salts and com-
pounds are also nontoxic.
203 In contrast, almost all organic tin compounds (tin compounds composed of carbon and
Guide to the Elements |
hydrocarbons) are very toxic and should be avoided. If they are used, special equipment and care must be taken in handling.
(Note: When chemical formulas use the letter “R” preceding an element’s symbol, it des- ignates some form of organic compound—for example, R 4 Sn. If the letter “X” follows the element’s symbol in a formula, it designates some form of inorganic compound—for example, SnX 2 . Thus, a whole series of tin compounds could be designated as R 4 Sn 2 ,R 2 Sn, or SnX 4 , SnX 2 , and so forth.)
LEAD SYMBOL:Pb PERIOD:6 GROUP:14(IVA) ATOMICNO:82
ATOMICMASS:207.19amu VALANCE:2and4 OXIDATIONSTATE:+2and+4 NAT- URALSTATE:Solid ORIGINOFNAME: Thename“lead”istheoldAnglo-Saxonwordforthiswell-knownele- ment,andthesymbolforlead(Pb)isderivedfromtheLatinword plumbum,which isalsotherootwordfor“plumber,”relatedtotheuseofleadpipesinancientRoman plumbingsystems.Someoftheseleadpipescanstillbeseeninpartsofmodern-day Rome.
ISOTOPES:Thereare47isotopesoflead,fourofwhicharestable.OneofthesefourisPb-
204,whichmakesup1.4%ofthenaturalabundanceofleadfoundonEarth.Inrealitythis isotopeisnotstablebuthasahalf-lifethatissolong(1.4×10 +17 years),withsomeofthe ancientdepositsstillexisting,thatitisconsideredstable.Theotherthreestableisotopesof leadandtheirproportiontothetotalnaturalabundanceareasfollows:Pb-206=24.1%, Pb-207=22.1%,andPb-208=52.4%.Alltheotherisotopesareradioactive.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=32
s2,p6,d10,f14
5-O=18
s2,p6,d10
6-P=4
s2,p2
Properties Lead is a bluish-white, heavy metallic element with properties that are more metal-like than
the properties of metalloids or nonmetals. Lead can be found in its native state, meaning that elemental metallic lead can be found in deposits in the Earth’s crust. However, most lead is first mined as galena ore (lead sulfide, PbS). The galena is mixed with lead sulfate, lead sulfide,
204 | The History and Use of Our Earth’s Chemical Elements and lead oxide and is then roasted at a high temperature. The air supply is reduced, followed
by an increase in heat and the vaporization of the sulfates and oxides of lead, which are drawn off as gases. The molten lead is then recovered.
Lead is only slightly soluble in water. However, it is also toxic. This is the reason lead is no longer used to pipe fresh water into homes. It does not react well with acids, with the exception of nitric acid. Lead’s melting point is 327.46°C, its boiling point is 1,740°C, and
its density is 11.342 g/cm 3 .
Characteristics Although lead can be found as a metal in the Earth’s crust, it is usually mined and refined
from minerals and ores. Lead is one of the most common and familiar metallic elements known. Although it is somewhat scarce, found at proportions of 13 ppm, it is still more preva- lent than many other metals. Lead is noncombustible. and it resists corrosion.
When lead, which is very soft, is freshly cut, it has shiny blue-white sheen, which soon oxidizes into its familiar gray color. Lead is extremely malleable and ductile and can be worked into a variety of shapes. It can be formed into sheets, pipes, buckshot, wires, and powder. Although lead is a poor conductor of electricity, its high density makes it an excellent shield for protection from radiation, including X-rays and gamma rays.
AbundanceandSource Lead is the 35th most abundant element on Earth. Although it has been found in its free
elemental metal state, it is usually obtained from a combination of the following ores: galena (PbS), anglesite (PbSO 4 ), cerussite (PbCO 3 ), and minum (Pb 3 O 4 ). Lead ores are located in Europe (Germany, Rumania, and France), Africa, Australia, Mexico, Peru, Bolivia, and Canada. The largest deposits of lead in the United States are in the states of Missouri, Kansas, Oklahoma, Colorado, and Montana.
One of the most famous mining towns is the high-altitude western city of Leadville, Colorado. The boom started with the gold rush of the 1860s, followed by silver mining in the 1870s and 1880s. Today, this city is the site of mining operations not only for lead, but also for zinc and molybdenum. At the height of its fame, Leadville had a population of almost 50,000 people. Today the population is about 2,500.
Lead is commonly obtained by roasting galena (PbS) with carbon in an oxygen-rich envi- ronment to convert sulfide ores to oxides and by then reducing the oxide to metallic lead. Sulfur dioxide gas is produced as a waste product. Large amounts of lead are also recovered by recycling lead products, such as automobile lead-acid electric storage batteries. About one- third of all lead used in the United States has been recycled.
History Although lead is not one of the most common metals on Earth, it is one of the best known.
The metallic forms of lead, mercury, arsenic, antimony, bismuth, and zinc were not known as separate elements in ancient times until methods were developed to analyze these ores and their metals. The widespread knowledge of lead is attributed to the ancient Romans, who developed many practical uses for this heavy metal. Lead-lined pipes were used by the ancient Romans to bring water from their famous aqueducts to their homes. In addition, most of the population of Rome cooked their food in pots and pans made of lead and lead alloys. Because
205 lead is slightly soluble in water, it is possible that much of the population was poisoned, to
Guide to the Elements |
some degree, by lead. Although there is scant evidence that mass lead poisoning existed, it has been speculated that lead pipes and cooking utensils may have helped accelerate the decline of the Roman Empire.
Lead was also known in other regions of the ancient world. Lead sculptures, coins, and other artifacts have been found in Egyptian tombs dating back to 5000 BCE. Lead was also known in ancient biblical times and is mentioned in the books of Job and Exodus.
CommonUses Lead has many uses and is an important commercial commodity. One of the most com-
mon uses is in the acid-lead electrical storage batteries used in automobiles. Much of the lead in these devices can be recycled and used again.
In the past, tetraethyl lead was added to gasoline to slow its burning rate in order to prevent engine “knock” and increase performance. This caused serious and harmful pollution, and lead has since been eliminated as a gasoline additive in most countries. Most exterior (and some interior) house paints once contained high levels of lead as well. Today, the amount of lead in paint is controlled, with not more than 0.05% allowed in the paint material.
Lead is used to make a number of important alloys. One is solder, an alloy of 1/2 lead and 1/2 tin. Solder is a soft, low-melting metal that, when melted, is used to join two or more other metals—particularly electrical components and pipes.
Babbitt metal is another alloy of lead that is used in the manufacture of wheel bearings that reduces friction. Lead is an ingredient in several types of glass, such as lead crystal and flint glass.
TV screens are coated with lead to absorb any radiation projected by the mechanism, and over 500,000 tons of lead is used in consumer electronics (computers, phones, games, and so on). Much of it ends up in solid waste dumps.
Many lead compounds are poisonous; thus, their uses in insecticides and house paints have been limited as other less toxic substances have been substituted. For example, lead arsenate
[Pb 3 (AsO 4 ], which is very poisonous, has been replaced in insecticides by less harmful sub-
stances. ExamplesofCompounds
Lead has a great range of oxides, many of which are of commercial importance. Although lead’s two common oxidation states are +2 and +4, it can also combine in +1 and +3 oxida- tion states.
Lead (I) suboxide (Pb 2 O) is the thin black film that forms naturally on a freshly cut piece of lead and that retards further oxidation. Lead (III) oxide (Pb 2 O 3 ) is a reddish-yellow solid used to manufacture glass, glazes, enamels, and the like. It is also used as a packing substance between pipe joints. Some examples of lead +2 and +4 are as follows:
Lead (II) chloride (PbCl 2 ) is commonly known as the mineral cotunnite. Lead (IV) oxide (PbO 2 ) is also known as lead dioxide. It is a brown substance important in the operation of the lead-acid storage battery. Lead arsenate [Pb 3 (AsO 4 ) 4 ] is a toxic commercial insecticide and herbicide.
206 | The History and Use of Our Earth’s Chemical Elements Lead carbonate (PbCO 3 ) is found in nature as cerussite. It can also be produced in the
laboratory by reacting sodium carbonate with chlorine. It is a crystalline poison that was, and to a lesser extent still is, used as a pigment in white house paints.
Lead chromate (PbCrO 4 ) is found in nature as yellow crystals in the mineral crocoite. It can be produced by reacting lead chloride and sodium dichromate. It is a popular and safe yellow pigment.
Lead azide [Pb(N 3 ) 2 ] is very unstable and must be handled with care. It is used as a detona- tor of explosives.
Hazards Lead is probably one of the most widely distributed poisons in the world. Not only is the
metal poisonous, but most lead compounds are also extremely toxic when inhaled or ingested.
A few, such as lead alkalis, are toxic when absorbed through skin contact. Workers in industries using lead are subject to testing of their blood and urine to determine the levels of lead in their bodies’ organs. Great effort is made to keep the workers safe. Unfortunately, many older homes (built prior to 1950) have several coats of lead-based paints that flake off, which then may be ingested by children, causing various degrees of lead poisoning, including mental retardation or even death.
Young children are more susceptible to an accumulation of lead in their systems than are adults because of their smaller body size and more rapidly growing organs, such as the kidneys, nervous system, and blood-forming organs. Symptoms may include headaches, dizziness, insomnia, and stupor, leading to coma and eventually death.
Lead poisoning can also occur from drinking tap water contained in pipes that have been soldered with lead-alloy solder. This risk can be reduced by running the tap water until it is cold, which assures a fresher supply of water.
Another hazardous source of lead is pottery that is coated with a lead glaze that is not stabilized. Acidic and hot liquids (citrus fruits, tea, and coffee) react with the lead, and each use adds a small amount of ingested lead that can be accumulative. Lead air pollution is still
a problem, but not as great as before, given that tetraethyl lead is no longer used in gasoline. However, lead air pollution remains a problem for those living near lead smelting operations or in countries where leaded gasoline is still permitted.
Even though lead and many of its compounds are toxic and carcinogenic, our lives would
be much less satisfying without its use in our civilization.
The Nitrogen Group (Metalloids to Nonmetals): Periods 2 to 6, Group 15 (VA)