142 | The History and Use of Our Earth’s Chemical Elements CommonUses
142 | The History and Use of Our Earth’s Chemical Elements CommonUses
During the Middle Ages and even during the period of the early settlement of North America, silversmiths were considered important craftsmen in the community. They created many items such as dinner flatware, vases, pouring vessels, and eating utensils, as well as jew- elry required by well-to-do households.
Silver has a multitude of uses and practical applications both in its elemental metallic form and as a part of its many compounds. Its excellent electrical conductivity makes it ideal for use in electronic products, such a computer components and high-quality electronic equipment. It would be an ideal metal for forming the wiring in homes and transmission lines, if it were more abundant and less expensive.
Metallic silver has been used for centuries as a coinage metal in many countries. The amount of silver now used to make coins in the United States has been reduced drastically by alloying other metals such as copper, zinc, and nickel with silver.
In the mid-1800s, Thomas Wilberger Evans (1823–1897) introduced the practice of using an amalgam of silver, which is a solution-type alloy (mixture) of mercury and silver. (Sometimes tin is also added.) In essence, the mercury is used to “cement” or bind the silver so that it can be used as a filling for decayed teeth. Due to the toxic nature of mercury, fillings are now made with mercury-free, nontoxic compounds.
Silver is used as a catalyst to speed up chemical reactions, in water purification, and in special high-performance batteries (cells). Its high reflectivity makes it ideal as a reflective coating for mirrors.
Several of its compounds were not only useful but even essential for the predigital pho- tographic industry. Several of the silver salts, such as silver nitrate, silver bromide, and silver chloride, are sensitive to light and, thus, when mixed with a gel-type coating on photographic film or paper, can be used to form light images. Most of the silver used in the United States is used in photography.
Photochromic (transition) eyeglasses that darken as they are exposed to sunlight have a small amount of silver chloride imbedded in the glass that forms a thin layer of metallic silver that darkens the lens when struck by sunlight. This photosensitive chemical activity is then reversed when the eyeglasses are removed from the light. This chemical reversal results from a small amount of copper ions placed in the glass. This reaction is repeated each time the lenses are exposed to sunlight.
Crystals of silver iodide (AgI), in addition to being useful in photographic processing, are used to “seed” clouds. The atmospheric conditions (humidity and such) must be right for this to work because the tiny crystals act as “nuclei” on which moisture can condense with the expectation that the small droplets will become heavy enough to drop to earth—as rain.
ExamplesofCompounds Some examples of silver with its main oxidation state of +1 follow:
Silver(I) oxide: 2Ag 1+ +O 2- → Ag 2 O. Catalysts and lab reagent. Silver(I) chloride: Ag 1+ + Cl 1- → AgCl. Used in photographic films, to coat and silver glass, as an antiseptic, and to absorb infrared light in lenses. Other commercially valuable compounds of silver are as follows: Silver nitrate (AgNO 3 ): Photographic emulsions, antiseptic, silver plating, and inks.
143 Silver sulfate (Ag 2 SO 4 ): Lab reagent, highly toxic.
Guide to the Elements |
Silver peroxide (Ag 2 O 2 ): Used to manufacture silver-zinc cells (batteries).
Argyrol: Trade name for compound of silver and a protein that is used as an antiseptic to treat specific types of bacterial infections.
Hazards Silver is not toxic as a free, elemental metal, but many of its compounds, particularly its
nitrogen compounds, are toxic. Several silver salts—in particular, AgNO 3 —are deadly when ingested, even in small amounts. When ingested, the silver compounds are slowly absorbed by the body, and the skin turns bluish or black, a condition referred to as “argyria.” In the past, the eyes of newborn babies were swabbed with dilute silver nitrate to prevent blindness from STDs (sexually trans- mitted diseases, in particular gonorrhea). This procedure is no longer performed.
Several silver compounds are extremely explosive—for example, silver picrate, silver nitride, silver peroxide, silver perchlorate, and silver permanganate. They are used in various types of explosives and as concussion caps for rifle and pistol ammunition.
CADMIUM SYMBOL:Cd PERIOD:5 GROUP:12(IIB) ATOMICNO:48
ATOMICMASS:112.41amu VALENCE:2OXIDATIONSTATE:+2 NATURALSTATE: Solid ORIGINOFNAME:ThewordcadmiumisfromtheLatinwordcadmiaortheGreekword kadmeia,meaningthezincoxideore“calamine”thatcontainstheelementcadmium. ISOTOPES:Thereare52isotopesofcadmium.Forty-fourareradioactiveandartificially produced,rangingfromCd-96toCd-131.Ofthese52isotopes,therearefivestable isotopesplusthreenaturallyoccurringradioactiveisotopeswithextremelylonghalf-lives thatareconsideredascontributingtotheelement’snaturaloccurrenceintheEarth’s crust.Thethreenaturallyradioactiveisotopes(Cd-106,Cd-113,andCd-116)arethe longestknownbetaemitters.Theyaretwomillionyearsolderthanwhenthesolarsys- temwasformedabout4.5billionyearsago.Thefivestableisotopesandtheirpropor- tionalcontributionstotheelement’sexistenceonEarthareasfollows:Cd-108=0.89%, Cd-110=12.49%,Cd-111=12.80%,Cd-112=24.13%,andCd-114=28.73%.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6