162 | The History and Use of Our Earth’s Chemical Elements
162 | The History and Use of Our Earth’s Chemical Elements
More complex iridium compounds are possible as well, including the following:
Iridium potassium chloride (K 2 IrCl 6 ) is used as a black pigment to make black porcelain kitchen and bathroom fixtures. Iridomyrmecin (C 10 H 16 O 2 ) is one of the few colorless compounds of iridium. It is used to manufacture insecticides. Iridosmine is not a compound, but an alloy of iridium, osmium, and a small amount of platinum that is used to make fine-pointed surgical instruments and needles and to form the fine tips of fountain pens. It is used worldwide to make weights because it resists oxidation better than any other alloyed metals.
Hazards The elemental metal form of iridium is almost completely inert and does not oxidize
at room temperatures. But, as with several of the other metals in the platinum group, several of iridium’s compounds are toxic. The dust and powder should not be inhaled or ingested.
PLATINUM SYMBOL:Pt PERIOD:6 GROUP:10(VIII) ATOMICNO:78
ATOMICMASS:195.078amu VALENCE:2and4 OXIDATIONSTATE:+2and+4;also +3and+6 NATURALSTATE:Solid ORIGINOFNAME: Thename“platinum”isderivedfromtheSpanishwordplatina,which means“silver.” ISOTOPES:Thereareatotalof43isotopesforplatinum.Fiveofthesearestable,and anotherhassuchalonghalf-lifethatitisconsideredpracticallystable(Pt-190witha half-lifeof6.5×10 +11 years).Pt-190contributesjust0.014%totheproportionofplati- numfoundonEarth.Thestableisotopesandtheircontributionstoplatinum’sexistence onEarthareasfollows:Pt-192=0.782%,Pt-194=32.967%,Pt-195=33.832%,Pt- 196=25.242%,andPt-198=7.163%.Alltheotherisotopesareradioactiveandare producedartificially.Theyhavehalf-livesrangingfromafewmicrosecondstominutesto hours,andonehasahalf-lifeof50years(Pt-193).
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=32
s2,p6,d10,f14
5-O=17
s2,p6,d9
6-P=1
s1
163 Properties
Guide to the Elements |
Platinum is classed by tradition and commercial usefulness as a precious metal that is soft, dense, dull, and silvery-white in color, and it is both malleable and ductile and can be formed into many shapes. Platinum is considered part of the “precious” metals group that includes gold, silver, iridium, and palladium. It is noncorrosive at room temperature and is not soluble in any acid except aqua regia. It does not oxidize in air, which is the reason that it is found in its elemental metallic form in nature. Its melting point is 1,772°C, its boiling point is
3,827°C, and its density is 195.09g/cm 3 .
Characteristics Platinum is the main metal in the platinum group, which consists of metals in both period
5 and period 6. They are ruthenium (Ru), rhodium (Ro), and palladium (Pd) in period 5 and osmium (Os), iridium (Ir), and platinum (Pt) in period 6. All six of these metals share some of the same physical and chemical properties. Also, the other metals in the group are usually found in platinum ore deposits.
Platinum can absorb great quantities of hydrogen gas, which makes it useful as a catalyst in industry to speed up chemical reactions.
AbundanceandSource Platinum is the 75th most abundant element and, unlike many elements, is found in its
pure elemental form in nature, as are deposits of silver and gold. Platinum is widely distributed over the Earth and is mined mainly in the Ural Mountains in Russia and in South Africa, Alaska, the western United States, Columbia in South America, and Ontario in Canada.
When found in the mineral sperrylite (PtAs 2 ), it is dissolved with aqua regia to form a pre- cipitate called “sponge” that is then converted into platinum metal. It is also recovered as a by-product of nickel mining, mainly in Ontario, Canada.
History There is archeological evidence that native platinum was known and used by the ancient
Egyptians as early as the seventh century BCE. A platinum metal burial-type box or casket was found in a tomb dating from that period. There is also evidence that pre-Columbian natives of South America used platinum several centuries later. In 1735 Spanish astronomer Antonio
de Ulloa (1716–1795) described a free metal he found in South America that was heavier than gold, had a higher melting point, and was noncorrosive. He named it platina, which is the Spanish word for “silver.” He is given credit for the discovery of platinum. Samples of plati- num ore from South America were sent in the 1700s for analysis in Europe, where in 1741 it was “rediscovered” by the Englishman Charles Wood (dates unknown).
An interesting bit of history regarding platinum occurred in 1978, when a defector from the Communist state of Bulgaria was assassinated when he was shot by a small platinum slug that contained a deadly poison. Because platinum is inert, there was no infection or inflamma- tion, and the physicians did not detect the wound until it was too late to save his life.
CommonUses Because of its chemical and physical properties, platinum has many uses. It is used widely
in jewelry making and is often mixed with gold to improve gold’s strength and durability.