164 | The History and Use of Our Earth’s Chemical Elements In the early 1800s it was known that when hydrogen is passed over powdered platinum, the
164 | The History and Use of Our Earth’s Chemical Elements In the early 1800s it was known that when hydrogen is passed over powdered platinum, the
hydrogen ignites without being heated and without consuming the platinum. This property led to a major use of platinum as a catalyst to speed up chemical reactions. An example is pres- ent in the internal combustion engine that produces harmful gases. Gasoline fuel burns inside the engine, as compared to the steam engine, where the fuel is burned outside the engine. The catalytic converter in automobiles uses a platinum-coated ceramic grid in the exhaust system to convert unburned fuel to carbon dioxide and water. The platinum in the converter will last as long as the car since a catalyst is not consumed by the chemical reaction.
As a catalyst, platinum is used for hydrogenation of liquid vegetable oils to produce solid forms of the oil, such as margarine. It is also used in the cracking process that breaks down large crude oil molecules into smaller, more useful molecules, such as gasoline. The catalytic
properties of platinum make it useful in the production of sulfuric acid (H 2 SO 4 ) and in fuel cells that unite hydrogen and oxygen to produce electricity. Platinum and some of its alloys have about the same expansion rate as glass, meaning that platinum wires can be inserted and sealed in glass structures such as bulbs and globes used for X-ray and other medical electronic equipment. Due to platinum’s inertness and ductile property, it can be formed into wires that are inserted into the human body, such as those used in electronic cardiac pacemakers. Platinum’s malleability permits it to be ham- mered into extremely thin sheets (only about 100 molecules thick) that are then used to plate the nose cones of missiles, fuel nozzles of jet engines, and the cutting edge of some instruments.
Platinum electrodes are attached to ocean-going ships and steel pipes and other submerged devices to help prevent corrosion from seawater. An alloy of platinum and iridium is used to form the standard weight for the kilogram, which is the basic unit of mass for the metric system. It is kept in a special vault in Paris, and all metric weights, worldwide, are judged for accuracy against this standard kilogram. Powdered platinum is used in air filters for spacecraft
and highflying aircraft to convert high altitude ozone (O 3 ) into oxygen (O 2 ). Ozone is a poi- sonous gas found in the upper atmosphere.
More recently it was found that some compounds of platinum slow the growth of certain types of cancer. Research continues to ascertain how platinum can contribute to the reduction of ovarian and testicular tumors.
ExamplesofCompounds Platinum has found many uses as an alloy with other metals, but it does form compounds
with the halogens in its +2 and +4 oxidation states. It also forms many compounds with oxygen in both these oxidation states as well as in +3 and +6 oxidation states. A few examples follow:
Platinum (II) chloride: Pt 2+ + 2Cl 1- → PtCl 2 . Platinum (IV) fluoride: Pt 2+ + 4F 1- → PtF 4 . Platinum (III) oxide: Pt 3+ + 3O 2- → Pt 2 O 3 . Platinum (IV) oxide (Pt 4+ + 2O 2- → Pt O 2 ) is also known as platinum dioxide. It is a dark-
brown to black powder known as Adams catalyst that is used as a hydrogenation catalyst. Chloroplantinic acid (H 2 PtCl 6 ) is one of the most commercially important compounds of platinum. Its many uses include etching on zinc, making indelible ink, plating, and coloring in fine porcelains and use in photography, in mirrors, and as a catalyst.
165 Hazards
Guide to the Elements |
Fine platinum powder may explode if near an open flame. Because platinum is rather inert in its elemental metallic form, it is not poisonous to humans, but some of its compounds, particularly its soluble salts, are toxic if inhaled or ingested.
GOLD SYMBOL:Au PERIOD:6 GROUP:11(1B) ATOMICNO:79
ATOMICMASS:196.967amu VALENCE:1and3 OXIDATIONSTATE:+1and +3 NATURALSTATE:Solid
ORIGINOFNAME: Thename“gold”isAnglo-SaxonaswellasfromtheSanskritwordjaval. ThesymbolAuisfromtheLatinwordaurum,whichmeans“shiningdawn.”
ISOTOPES:Thereareatotalof54isotopesofgold,onlyoneofwhichisstable:Au-197, whichaccountsfortheelement’stotalnaturalexistenceonEarth.Theremaining53iso- topesareradioactive,areartificiallyproducedinnuclearreactorsorparticleaccelerators, andhavehalf-livesrangingfromafewmicrosecondstoafewsecondstoafewhoursto
afewdays.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18