Rhodium is a chemical element. It has the chemical symbol Rh. It has the atomic number 45. It is a rare metal. It is silver white and hard. In chemistry it is placed in a group of metal elements named the transition metals. It is also part of the platinum group. Rhodium is found in platinum ores.
Rhodium is used as a catalyst in some platinum alloys. It is the most expensive precious metal.
Tellurium
Tellurium is a chemical element. It has the chemical symbol Te and the atomic number 52. It has 52 protons and 52 electrons. Its mass number is 127.6. It has 8 natural isotopes. 4 are stable and 4 are radioactive. One of the radioactive ones lasts longer than any other isotope. It has a half life of 2.2 x 10 years (2.2 septillion years).
It is a brittle silver-white semimetal. When it is pure it has a metallic shine. It is ground easily. It can be made in an amorphous form. It is a semiconductor. It changes conductivity a little when light shines on it, similar to selenium. It is corrosive to many metals when molten.
Tellurium is an unreactive element. It can react with reactive metals to make tellurides. It can burn in air to make tellurium dioxide. It can be oxidized even more to tellurium trioxide. It does not corrode. The chemistry of tellurium is similar to some chemistry of selenium and sulfur, although its compounds are more reactive and the element is less reactive. It does not dissolve in most acids, although it dissolves in concentrated sulfuric acid to make a special red tellurium cation.
Tellurium makes chemical compounds in several oxidation states: -2, +2, +4, and +6. -2 compounds are normally found in tellurides. They are strong reducing agents. Tellurides are normally the main ore of tellurium. Most natural tellurides are not pure, so they are much less reactive. +2 compounds are found in some tellurium halides, like tellurium(II) chloride and tellurium(II) bromide. They are the rarest oxidation state. +4 compounds are found in tellurites and tellurous acid. They are weak oxidizing agents, that can be reduced to tellurium. Tellurites are made by reacting tellurium dioxide with a metal oxide. +6 compounds are found in tellurates and telluric acid. They are powerful oxidizing agents. Tellurates are made by reacting telluric acid with metal oxides.
Tellurium is a very rare mineral. There is 14 times more silver in the earth than there is tellurium. Tellurium is sometimes found as an element, but most of the times is found as tellurides. Gold tellurides (Calaverite) are found in the earth. They are valuable ores of both tellurium and gold. This gold ore was not recognized as gold during one gold rush and was used as a filler. It was then discovered that it was gold telluride, making another gold rush. Telluride cannot replace sulfide in elements like selenide does.
Tellurium can be taken from gold telluride by dissolving the gold telluride in concentrated sulfuric acid. The tellurium dissolves to make a red solution, while the gold sinks to the bottom.
A more common way of extracting tellurium from tellurides is to heat the tellurides. The tellurides are heated with sodium carbonate and air. This makes sodium tellurite. Selenites are normally found as an impurity. They are separated by reacting them with sulfuric acid. The selenites stay in solution. The tellurites turn into tellurium dioxide. Then the tellurium dioxide is reacted with sulfur dioxide dissolved in sulfuric acid to make tellurium metal. The tellurium can be melted and reformed to make bars of tellurium metal.
The main use of tellurium is in alloys. It is used in iron, copper, and lead alloys. It makes the metals more easily machinable (able to be shaped by a machine). It improves strength and durability of lead and makes it more resistant to corrosion by sulfuric acid.
Tellurium is also used in cadmium telluride solar cells. These are very efficient. It can be alloyed with both cadmium and mercury to make mercury cadmium telluride, an infrared sensitive semiconductor. It is used in some rewritable (able to be erased and written again) optical discs. Lead telluride is used in another type of infrared sensor.
It is also used to color ceramics. It is used to make fiberglass that is used in telecommunications (telephones, internet, etc.). It helps increase the refraction. It is also used in delay blasting caps. Rubber can be ha.
Tellurium is not really used in any living things. Some fungi, though, can use tellurium instead of selenium or sulfur. Most organisms can metabolize tellurium to make dimethyl telluride, which is a garlic-smelling chemical. If someone eats a tellurium compound, it gives them garlic breath.
Tellurium is very toxic.
Indium
Indium is a chemical element. It has the chemical symbol In. It has the atomic number 49. It is a rare metal. It is a soft, malleable and poor metal. Indium looks like zinc. Pieces of indium can easily be joined together by pushing one piece into another. The chemistry of indium is quite like aluminium or gallium. Zinc ores are the main source of indium.
The main use of indium is in the chemical compound Indium tin oxide in liquid crystal displays. It is also used in very thin layers as a lubricant. In World War II it was used a lot to coat bearings in aircraft.
Francium
Francium is a chemical element with the chemical symbol Fr and an atomic number of 87. It is a metal. In chemistry it is placed in a group of metal elements named the alkali metals. Francium is very radioactive. It is in very small amounts in uranium and thorium ores. It has the lowest electronegativity and electron affinity of all the chemical elements.
Francium reacts violently with water, as do all of the elements in group 1 on the periodic table.
Francium is one of the hardest to find elements on the planet Earth. It is estimated that there are only about 15 grams or half an ounce in the Earth's crust at a single time.
Although chemists knew the element number 87 in the periodic table should exist, it was a long time before it was discovered. In the early 1900s, nearly all boxes on the periodic table had been filled. Chemists knew that one element had been found to fit into each box. Francium was discovered in 1939 by a French chemist called Marguerite Perey. She named it after her home country, France.
There are 34 known isotopes of francium ranging in atomic mass from 199 to 232. Francium-223 and francium-221 are the only isotopes that occur in nature.
Francium-223 is the most stable isotope, with a half-life of 21.8 minutes. Francium-223 is the fifth product of the actinium decay series as the daughter isotope of actinium-227. Francium-223 then decays into radium-223 by beta decay (1.149 MeV decay energy), with a minor (0.006%) alpha decay path to astatine-219 (5.4 MeV decay energy).
Francium-221 has a half-life of 4.8 minutes. It is the ninth product of the neptunium decay series as a daughter isotope of actinium-225. Francium-221 then decays into astatine-217 by alpha decay (6.457 MeV decay energy).
Rhenium
Rhenium is a chemical element. It has the chemical symbol Re. It has the atomic number 75. It is a rare metal. It is silver white. In chemistry it is placed in a group of metal elements called the transition metals. The chemistry of rhenium is similar to manganese. Discovered in 1908, rhenium was the second-last stable element to be discovered ('stable' meaning not radioactive). It was named after the river Rhine in Europe.
Nickel-based superalloys of rhenium are used in the combustion chambers, turbine blades, and exhaust nozzles of jet engines. These alloys contain up to 6% rhenium, making jet engine construction the largest single use for the element. The second-most important use is as a catalyst: rhenium is an excellent catalyst for hydrogenation and isomerization.
Rhenium found as a by-product of molybdenum refinement.
Rhenium is used in some manganese alloys. Rhenium-molybdenum alloys are superconductors.