For a while now, I've been posting articles on Hansisgreat about each of the elements in the Periodic Table. As it turns out, even the most obscure elements have interesting stories and uses. Today, I'm posting on three metals...
Atomic Symbol: Pd
Atomic Number: 46
Palladium is part of a wider story that led to the discovery of four previously unknown elements (palladium, rhodium, osmium, and iridium) by London chemists Wollaston and Tennant. Wollaston brought most of his palladium to a jewelry store in 1803, where it was sold as "new silver", costing six times as much as gold. Attempts were made to popularize the metal as an untarnishable silver, and it was often used in medals presented to royalty commemorating important events.
The metal's main industrial use is in catalytic converters for cars, which relied on platinum until 1990, when palladium was discovered to be much more effective at removing hydrocarbons from fuel exhaust. It is also added to gold jewelry to give it a bright luster, known as "white gold".
Palladium was named for the asteroid Pallas, discovered the same year as the element.
Atomic Symbol: Ag
Atomic Number: 47
Slag heaps near ancient mines reveal that silver has been used by man since 3000 BC. When it first appeared in Egypt, it was more valuable than gold. Silver was refined by a process called cupellation, discovered by the Chaldeans and described in the Bible (Ezekiel 22: 17-22).
Medieval physicians sold silver nitrate, which they called lunar caustic, for relief of various ailments. Medical treatment with silver has its drawbacks, however: it causes grayness of the skin, hair, and eyes; a condition known as argyria.
In 1884, German obstetrician Dr. F. Crede showed that silver nitrate eye drops could be used to prevent blindness in infants by killing the microbial infection that caused the disease. In fact, silver is poisonous to virtually all microorganisms.
Photography would be impossible without silver. This is because some of its compounds are sensitive to light. Silver has also been used for centuries to purify drinking water, which explains why silver coins are found at the bottom of many wells.
Atomic Symbol: Cd
Atomic Number: 48
One of the most controversial elements, because in spite of its many industrial uses, cadmium is toxic to humans and can remain in the body for as long as 30 years once it is ingested.
In spite of this drawback, nickel-cadmium batteries are quickly replacing lead-based batteries because they are much lighter, and more environmentally friendly: they can be recharged a thousand times or more and still work well. Nissan and Volkswagen are both producing electric cars which rely on these batteries, and use not a drop of oil for fuel. They are expected to be on the market in 2010.
Solar panels constructed of cadmium metal have exceptional efficiency for converting sunlight into electricity. A square meter of such a panel can generate a power output of over 100 watts.
This element is only very slightly radioactive. Out of every million cadmium atoms that date from the creation of the Universe, 15 billion years ago, only one has since disintegrated.
There's an amazing book on the Periodic Table called Nature's Building Blocks: An A-Z Guide to the Elements, by John Emsley. It's been an invaluable resource for me when writing these chemistry posts, and is highly recommended for the chemistry enthusiast.
For my posts on the previous 45 elements, click here.