In fact, I knew absolutely nothing about the three Elements I'm posting on today until I started researching them for this post. All three turned out to have interesting stories I couldn't have imagined. Please enjoy...
Atomic Symbol: Se
Atomic Number: 34
In 1975, selenium was discovered to be an essential element for human life. In fact, every cell in the body contains more than a million atoms of this element! The concentration is highest in the testicles, and selenium deficiency is a leading cause of low sperm count.
Metallic selenium conducts electricity; it is a better conductor of electricity in light than in darkness, the conductivity varying directly with the intensity of the light. It is therefore used in many photoelectric devices, such as copy machines.
One of its other common industrial uses is to decolorize and tint glass, since it counteracts the greenish glow created by iron. It can produce a wide variety of colors: reds, yellows, and vermilions. In this way, selenium was used to stain glass centuries before it was discovered and understood.
The idea of television was first proposed in the 1860s, and in the 1880s experiments were tried using selenium to transmit motion pictures over wires. Sadly, the experiments were a failure.
Atomic Symbol: Br
Atomic Number: 35
Although no one realized it at the time, this element was responsible for the famous Tyrian purple which was so prized by Roman emperors. This naturally occurring dye was extracted from Mediterranean mollusks, and was known in the Middle East centuries before the Romans. It's mentioned several times in the Old Testament.
Bromine is the name of the element, which exists as the molecule Br2 , called bromide. It is used in industry to produce organobromo compounds for insecticides, in fire extinguishers, and to make pharmaceuticals. Some of these uses have come under suspicion, because large concentrations of these chemicals leak into the surrounding environment.
Although a small amount of bromide is present in all living things, larger doses are not without effect, most noticeably as a depressed sex drive.
Atomic Symbol: Kr
Atomic Number: 36
This element is one of the rarest gases in the atmosphere, but there are still more than 15 billion tons of Krypton circulating this planet. It has no role in any part of the environment because it is almost totally inert chemically and of low solubility in water.
About 8 tons a year are extracted for industrial use, via liquid air. For example, it is used in lasers and to color "neon" lights.
Radioactive Krypton-85 has a half life of 11 years and is given off by nuclear reactions. It escapes to the atmosphere but is not considered pollution because it is inert. The level of this gas in the atmosphere was carefully monitored during the Cold War because it revealed the extent of the Soviet bloc's production of nuclear material.
This element is privileged to have Superman's home planet named in its honor. The green mineral kryptonite, famous as Superman's only weakness, is completely fictional.
My previous posts on the elements are here.
There's a great book of reference on the subject, which has been invaluable to me while researching these posts. Check out Nature's Building Blocks, by John Emsley.