Silicon is a chemical element. Its atomic number is 14 on the periodic table. Its symbol is Si. It is a hard, brittle crystalline solid. It is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic table.
Silicon looks like a metal, but does not do everything a metal does, like conduct electricity very easily. Silicon is used as a great deal in today's computers and virtually every electronic device. Germanium can also be used in computers, but silicon is easier to find.
There is a lot of silicon on the Earth. At the beach, there is silicon in the form of sand. Sand is a compound of silicon known as silicon dioxide or silica. Glass is made by heating sand (or silicon dioxide) hot enough. The glass can have different colours by adding coloured compounds. Silicon also makes up a lot of different rocks and minerals, and they are known as silicates.
Silicon is a semiconductor, and much used in computers. A super-pure isotope of silicon, silicon-28, can now be made 40 times more pure than before. It is very important for the next big development in computers. This stores "qubits" in atoms of another element, like phosphorous, embedded in a tiny layer of ultra-pure silicon-28. These qubits can simultaneously encode a one and a zero, for incredibly fast and complex calculations.
Cadmium
Cadmium is a metal. It is element 48 on the periodic table. Its symbol is "Cd". Its atomic number is 48 and its atomic mass is 112.4. It is found in Group 12 on the periodic table.
Cadmium is a blue-gray soft metal. It can be considered a transition metal or a post-transition metal. It is malleable and ductile. It is similar to zinc. It melts at 321°C.
Cadmium has 8 natural isotopes. 5 are radioactive, but 3 have very long half-lives so their radioactivity is almost nothing.
Cadmium is a moderately reactive metal. It corrodes in moist air and dissolves in acids. It burns in air when powdered to make the brown cadmium oxide.
Cadmium forms chemical compounds in two oxidation states: +1 and +2. The +1 state is rare and unstable. The +2 state is much more common. Most +2 compounds dissolve easily in water and are white to yellow. Cadmium oxide can be brown, red, or white. Cadmium sulfide is bright yellow. Cadmium chloride and cadmium sulfate are colorless solids that dissolve easily in water. Cadmium fluoride is slightly soluble. Cadmium compounds are toxic when inhaled.
Cadmium was found by two chemists, German chemist Friedrich Stromeyer discovered it in 1817, and Karl Herman also discovered it in 1818. They were looking at an impurity in zinc carbonate and found cadmium. For about 100 years, Germany made most cadmium. Cadmium iodide was used as a medicine although it was toxic.
Cadmium ores are rare. Greenockite, a cadmium sulfide mineral is the only main ore and it is found with sphalerite, a zinc sulfide. Because of this, most cadmium comes from zinc processing. Cadmium as a metal is very rare but is found in one place in Russia.
China makes the most cadmium. South Korea and Japan also make cadmium. Cadmium is taken from the zinc metal by heating the zinc metal in a vacuum. Cadmium is boiled first. The cadmium is condensed and used. Cadmium is also taken by precipitating it from the solution of zinc sulfate used to make pure zinc by electrolysis.
In the 1930s and 1940s cadmium was mainly used to plate steel to prevent it from corroding. Then cadmium sulfide was used as a pigment in paint.
Now, cadmium is mainly used in nickel cadmium batteries. 86% of cadmium is used in batteries as of 2009. Some people are trying to stop using nickel-cadmium batteries because cadmium is toxic. Cadmium is still used to electroplate steel to prevent corrosion. Only about 6% of cadmium is used for this. Cadmium is also used in lasers, nuclear reactors, phosphors, photoresistors, pigments, and semiconductors. Wood's metal, an alloy that melts very easily, has cadmium in it. Cadmium is used in some solder.
Cadmium is not used in the human body or any other animal. A diatom uses cadmium, though.
Cadmium is a highly toxic metal. Dust of cadmium or its compounds is very dangerous and can kill. Some countries have banned cadmium from electronics. Cigarette smoking is the most important source of cadmium. Smokers have about 4 times more cadmium in their blood than nonsmokers (people who do not smoke). Cadmium is thought to be carcinogenic, although people still debate whether it is other things with the cadmium that cause cancer, like arsenic.
Krypton
Krypton is a noble gas which means it does not react with many other elements. It is clear and has no taste or smell. The atmosphere is only about one millionth part krypton. The name "kypton" comes from the Greek word "kryptos" meaning hidden. It is used in fluorescent lamps, flashbulbs, and as a wavelength standard. The metre used to be defined as 1,650,763.73 wavelengths in a vacuum of krypton gas. Krypton has very few compounds.
The main use for krypton is to make light. There is one main type of krypton light bulbs. This is called a gas discharge lamp. There are three main types of these. First is a low energy gas discharge lamp or "neon light". Low energy gas discharge lights made from krypton are near white to green. Second is a high energy short length of time gas discharge light or "flash bulb". These are mostly used for photography. They are bright blue-white. Third is a high energy gas discharge light. This third kind is mostly used to light airport runways. They are also bright blue-white.
Krypton is number 36 on the periodic table. Its symbol is Kr.
Krypton was found by Sir William Ramsay and Morris Travers in Great Britain in 1898. Ramsay was given the 1904 Nobel Prize in Chemistry for his work on noble gases. It was a difficult gas to discover; Ramsay suspected it existed but only found it by removing other gases. This is why he gave it the name Krypton. There is no mineral called Kryptonite or planet called Krypton, which features in the Superman comics by Jerry Siegel and Joe Shuster. The fictional planet is probably better known than the real chemical element called Krypton.
Noble gas
The noble gases are a group of elements that are all gases. These elements are all in group 18 of the periodic table. All of them are monoatomic, meaning each molecule is a single atom. They almost never react with other elements. This is because they have a full 8 electrons outer electron shell. There are six noble gases:
All of these gases are found in air. They make up around 0.96% of the atmosphere. Noble gas compounds can be formed from noble gases.
When the noble gases are used in cold cathode tubes to produce light, each of them has a different colour. Since Radon is radioactive, it is usually not used for lighting. Here are pictures of what the others look like:
Oganesson (element 118) is probably the next noble gas after Radon because it is the next box down in the same group. However it has a half life of 0.89 ms, after which it decays to Livermorium (Element 116). This means its use is probably limited.
Noble gases were discovered by Lord Rayleigh and Sir William Ramsay. Rayleigh won the Nobel Prize in Physics in 1904 for his work on noble gas. Ramsay won the Nobel Prize in Chemistry in 1904 for his work with noble gas.
Polonium
Polonium is a rare radioactive metalloid. It is chemical element 84 on the periodic table and its symbol is Po. It was discovered in 1898 by Marie and Pierre Curie.
Polonium is highly unstable, radioactive and toxic. This makes it difficult to handle. It can be dangerous, even in very small amounts. One gram of Po will self-heat to a temperature of about . It also vaporizes easily.
Polonium has 33 isotopes, and all of them are radioactive. It is a very rare element in nature because of its short half-life. It is a breakdown product of uranium, so it is found in uranium ores.
Polonium is also very important because it the main element of nuclear bombs.
Bismuth