236 | The History and Use of Our Earth’s Chemical Elements CommonUses
236 | The History and Use of Our Earth’s Chemical Elements CommonUses
Sulfur is one of the four major commodities of the chemical industry. The other three are limestone, coal, and salt. Most sulfur that is produced is used to manufacture sulfuric acid (H 2 SO 4 ). Forty million tons are produced each year in the manufacture of fertilizers, lead-acid batteries, gunpowder, desiccants (drying agent), matches, soaps, plastics, bleaching agents, rubber, road asphalt binders, insecticides, paint, dyes, medical ointment, and other pharma- ceutical products, among many, many other uses. Sulfur is essential to life.
ExamplesofCommonCompounds Hydrogen sulfide (H 2 S) is one of the most important compounds of sulfur. It is a colorless
gas with a foul, rotten-egg odor. It is well known in school laboratories when sulfur is being studied. It is produced by the reaction of hydrochloric acid with iron sulfide (2HCl + FeS →
FeCl 2 +H 2 S). Sulfur dioxide (SO 2 ) has many uses, including as a bleaching agent, solvent, disinfectant, and refrigerant. It is mostly used in the production of sulfuric acid. Sulfur dioxide is generated by burning sulfur in air, resulting in the following chemical reaction: S + O 2 → SO 2 . Sulfur dioxide can also be produced by roasting metal sulfides and by the reaction of acids with metallic sulfides. Sulfur dioxide combines with water to form a weak acid known as sulfurous
acid (SO 2 +H 2 O→H 2 SO 3 ). Sulfur chloride (S 2 Cl 2 ) is combustible and will react when in contact with water. It is used to produce carbon tetrachloride, to purify sugar juices, to extract gold from its ore, in insecti- cides, and as a poisonous gas for military/combat purposes.
Sulfuric acid (H 2 SO 4 ), also known at battery acid, is the leading chemical manufactured in the United States, with an annual production of 40 million tons per year. Most of it is used in the manufacture of fertilizers, explosives, pigments, and dyes. It has the nasty attribute of being able to extract hydrogen and oxygen from organic substances, which can cause serious burns. It is strongly corrosive and, in both concentrated and weak solutions with water, will react with most metals.
Several steps are required in the production of sulfuric acid, as follows: S+O 2 → SO 2 2SO 2 +O 2 → 2SO 3
SO 3 +H 2 SO 4 →H 2 S 2 SO 7
H 2 S 2 O 7 +H 2 O → 2H 2 SO 4 Because there are so many metal sulfides, chemists usually use the letter “M” in the formula
to indicate that sulfur can combine with just about any metal (e.g., MHS, M 2 S, M 2 S 3 , and so on). Sulfate ions (SO 2- 4 ) also combine with many different metal atoms to form common compounds, such as copper sulfate (CuSO 4 ) and magnesium sulfate, calcium sulfate, lead sulfate, zinc sulfate, and barium sulfate. There are four major phosphorous–sulfur compounds, ranging from P 4 S 3 to P 4 S 10 , and there are six important oxygen–sulfur compounds, ranging from SO to S 2 O 7 , the most impor- tant being sulfur dioxide (SO 2 ), which can react as both an oxidizing and a reducing agent.
237 Hazards
Guide to the Elements |
Many of the sulfur compounds are toxic but essential for life. The gas from elemental sul- fur and from most of the compounds of sulfur is poisonous when inhaled and deadly when ingested. This is the reason that sulfur compounds are effective for rat and mice extermination as well an ingredient of insecticides. Sulfa drugs (sulfanilamide and sufadiazine), although toxic, were used as medical antibiotics during World War II before the development of penicil- lin. They are still used today in veterinary medicine.
SELENIUM SYMBOL:Se PERIOD:4 GROUP:16(VIA) ATOMICNO:34
ATOMICMASS:79.96amu VALENCE:2,4,and6 OXIDATIONSTATE:–2,+4,and +6 NATURALSTATE:Solid.
ORIGINOFNAME:NamedfortheGreekwordselene,meaning“moon.”JonsJacobBerze- lius(1779–1848)discoveredseleniumandnameditafterthemineralcalled“eucairite,” whichinGreekmeans“justintime.”
ISOTOPES:Thereareatotalof35isotopesofselenium.Fiveofthesearestable,and asixthisotopehassuchalonghalf-lifethatitisalsoconsideredstable:Se-82= 0.83×10 +20 years.Thissixthisotopeconstitutes8.73%ofselenium’sabundanceinthe Earth’scrust,andtheotherfivestableisotopesmakeuptherestofselenium’sabun- danceonEarth.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=6
s2,p4
Properties Selenium is a soft metalloid or semimetal that is similar to tellurium, located just below
it in the oxygen group, and sulfur, which is just above it in the same group. Selenium has several allotropic forms that range from a gray metallic appearance to a red glassy appearance. These allotropic forms also have different properties of heat, conductivity, and density. In its amorphous state, it is a red powder that turns black and becomes crystalline when heated. Crystalline selenium has a melting point of 220°C, a boiling point of 685°C, and a density
of 4.809 g/cm 3 . Characteristics Crystalline selenium is a p-type semiconductor. It acts as a rectifier that can change electric
current from alternating current (AC) to direct current (to DC). It has photovoltaic proper-
238 | The History and Use of Our Earth’s Chemical Elements ties, meaning it is able to convert light (radiant) energy that strikes it into electrical energy.
Selenium’s resistance to the flow of electricity is influenced by the amount of light shining on it. The brighter the light, the better the electrical conductivity.
Selenium burns with a blue flame that produces selenium dioxide (SeO 2 ). Selenium will react with most metals as well as with nonmetals, including the elements in the halogen group
17. AbundanceandSource
Selenium is the 67th most abundant element in Earth’s crust. It is widely spread over the Earth, but does not exist in large quantities. As a free element it is often found with the ele- ment sulfur.
There is only one mineral ore that contains selenium: eucairite (CuAgSe). Although rich in selenium, it is too scarce to be of commercial use. Almost all selenium is recovered from the processing of copper and the manufacturing of sulfuric acid as a leftover sludge by-product. This makes selenium’s recovery profitable. Recovering it from eucairite is not profitable.
Selenium is found in Mexico, Bosnia, Japan, and Canada. It can be found in recoverable quantities in some soils in many countries.
History Selenium was discovered in the early 1800s by Jons Jakob Berzelius (1779–1848) along
with a friend Wilhelm Hisinger (1766–1852), who was a mineralogist. Berzelius believed tellurium was contaminating the product in a sulfuric acid factory. Later, he found it to be another element similar to tellurium. After isolating it, he identified it as element 34, which turned out to be selenium.
CommonUses The photosensitive nature of selenium makes it useful in devices that respond to the
intensity of light, such as photocells, light meters for cameras, xerography, and electric “eyes.” Selenium also has the ability to produce electricity directly from sunlight, making it ideal for use in solar cells. Selenium possesses semiconductor properties that make it useful in the elec- tronics industry, where it is a component in some types of solid-state electronics and rectifiers. It is also used in the production of ruby-red glass and enamels and as an additive to improve the quality of steel and copper. Additionally, it is a catalyst (to speed up chemical reactions) in the manufacture of rubber.
Selenium is an essential trace element for both plants and animals, and it is a diet supple- ment in animal feed as well as for humans.
ExamplesofCompounds Selenium forms a few important inorganic compounds. Some examples follow:
Selenium dioxide (SeO 2 ) is used as an oxidizing agent, as a catalyst, and as an antioxidant for lubricating oils and grease. Selenium sulfide (SeS 2 ) is used for some medicines, as an additive for medicated shampoos to control dandruff and scalp itching, and in treatment products for acne and eczema.
There are several different compounds of selenium and the halogen chlorine that range
from selenium dichloride (SeCl 2 ) to selenium oxychloride (SeOCl 2 ), which are used as solvents.
239 Hazards
Guide to the Elements |
The fumes and gases of most selenium compounds are very toxic when inhaled. SeO 2 and SeS 2 are toxic if ingested and very irritating to the skin. They are also carcinogenic. Although some compounds of selenium are poisonous, as an element it is essential in trace amounts for humans. It is recommended that 1.1 to 5 milligrams of selenium be included in the daily diet. This amount can be maintained by eating seafood, egg yokes, chicken, milk, and whole grain cereals. Selenium assists vitamin E in preventing the breakdown of cells and some chemicals in the human body.
TELLURIUM SYMBOL:Te PERIOD:5 GROUP:16 ATOMICNO:52
ATOMICMASS:127.60amu VALENCE:2,4,and6 OXIDATIONSTATE:+6,+4,and –2 NATURALSTATE:Solid
ORIGINOFNAME:Thename“tellurium”isderivedfromtheLatinwordforEarth,tellus. ISOTOPES:Thereareatotalof48isotopesoftellurium.Eightoftheseareconsidered
stable.Threeofthestableonesareactuallyradioactivebuthavesuchlonghalf-lives thattheystillcontributetothenaturalabundanceoftelluriuminthecrustoftheEarth. TheisotopeTe-123(half-lifeof6×10 +14 years)contributes0.89%ofthetotaltellurium foundonEarth,Te-128(half-lifeof7.7×10 +24 years)contributes31.74%tothenatural abundance,andTe-130(half-lifeof0.79×10 +21 years)contributes34.08%tothetel- luriumintheEarth’scrust.Theotherfivestableisotopesandthepercentageoftheir naturalabundanceareasfollows:Te-120=0.09%,Te-122=2.55%,Te-124=4.74%, Te-125=7.07%,andTe-126=18.84%.Theother40isotopesareallradioactivewith shorthalf-lives.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=18
s2,p6,d10
5-O=6
s2,p4
Properties Tellurium is a silver-white, brittle crystal with a metallic luster and has semiconductor
characteristics. It is a metalloid that shares properties with both metals and nonmetals, and it has some properties similar to selenium and sulfur, located just above it in group 16 of the periodic table.
240 | The History and Use of Our Earth’s Chemical Elements
There are two allotropic forms of tellurium: (1) the crystalline form that has a silvery metallic
appearance and a density of 6.24 g/cm 3 , a melting point of 499.51°C, and a boiling point of 988°C; and (2) the amorphous allotrope that is brown in color and has a density of 6.015g/cm 3 and ranges for the melting and boiling point temperatures similar to the crystalline form.
Characteristics The pure form of tellurium burns with a blue flame and forms tellurium dioxide (TeO 2 ).
It is brittle and is a poor conductor of electricity. It reacts with the halogens of group 17, but not with many metals. When it reacts with gold, it forms gold telluride. Tellurium is insoluble in water but readily reacts with nitric acid to produce tellurous acid. If inhaled, it produces a garlic-like odor on one’s breath.
AbundanceandSource Tellurium is the 71st most abundant element on Earth. It makes up a small portion of
igneous rocks and is sometimes found as a free element, but is more often recovered from several ores. Its major ores are sylvanite (AgAuTe 4 ), also known as graphic tellurium, calaverite, sylvanite, and krennerite, all with the same general formula (AuTe 2 ). Other minor ores are nagyagite, black tellurium, hessite, altaite, and coloradoite. In addition, it is recovered from gold telluride (AuTe 2 ). Significant quantities are also recovered from the anode “slime” of the electrolytic refining process of copper production.
History Two people are responsible for the discovery of tellurium. First, Franz Joseph Muller von
Reichenstein (1743–1825), chief inspector of a gold mine in Transylvania (part of Romania), experimented with the ores in his mine between 1782 and 1783. From an ore known as aurum album, he extracted an element that, at first, was thought to be antimony. He sent a sample to Martin Heinrich Klaproth (1743–1817), who 16 years later correctly identified it as a new element and named it tellurium. However, Klaproth gave Franz Joseph Muller credit for the discovery.
CommonUses Tellurium’s major use is as an alloy with copper and stainless steel. It makes these metals
easier to machine and mill (cut on a lathe). It is also used as a vulcanizing agent in the produc- tion of rubber, as a coloring agent for glass and ceramics, and for thermoelectrical devices.
Along with lithium, it is used to make special batteries for spacecraft and infrared lamps. Tellurium can be used as a p-type semiconductor, but more efficient elements can do a better job. It is also used as a depilatory, which removes hair from skin.
Although tellurium forms many compounds, most of them have little commercial value. ExamplesofCompounds
Following are examples of compounds associated with the three ions of tellurium, +2, +4 and +6.
Tellurium (II) dichloride (TeCl 2 ): Te 2+ + 2Cl 1- → TeCl 2 . Tellurium (lV) tetrachloride (TeCl 4 ): Te 4+ + 4Cl 1- → TeCl 4 .
Guide to the Elements |
Tellurium (VI) trioxide (TeO 3 ): Te 6+ + 3O 2- → TeO 3 .
Other compounds include the following: Tellurium dibromide (TeBr 2 ) forms blackish-green needles that are very hygroscopic (read- ily absorbs water). It is toxic when inhaled. Tellurium dichloride (TeCl 2 ) is similar to TeBr 2 , but in powder form it is greenish-yellow. It is also toxic when inhaled. Tellurium dioxide (TeO 2 ) is a whitish crystalline powder that is slightly soluble in water. It is also toxic when inhaled.
Hazards All forms of tellurium are toxic in gas form. The vapors of all the compounds of the dust
and powder forms of the element should not be inhaled or ingested. When a person is poi- soned with tellurium, even in small amounts, the breath will smell like garlic.
POLONIUM SYMBOL:Po PERIOD:6 GROUP:16 ATOMICNO:84
ATOMICMASS:210amu VALENCE:2,4,and6 OXIDATIONSTATE:+2and+4 NAT- URALSTATE:Solid ORIGINOFNAME:NamedforPoland,thenativecountryofMarieCurie,whodiscovered theelement. ISOTOPES:Thereare41isotopesofpolonium.TheyrangefromPo-188toPo-219.All ofthemareradioactivewithhalf-livesrangingfromafewmillisecondsto102years, thelatterforitsmoststableisotopePo-209.Poloniumisinvolvedwithseveralradio- activedecayseries,includingtheactiniumseries,Po-211andPo-215;thethorium series,Po-212andPo-216;andtheuraniumdecayseries,Po-210,Po-214,andPo- 218.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10