A photocell, also known as a photoresistor, is an electronic component, device that changes its electrical conductivity when light shines on it. In the picture, the electricity flows through the reddish part. Normally, when light shines on it, then more electricity flows through. When it is dark, almost no electricity flows through. Selenium can be used to make photocells, although some other chemicals can be used.
Semiconductors are used to make photocells. When the light shines into the photocell, it "loosen"s the electrons, allowing them to flow and make an electrical current.
Selenium dioxide
Selenium dioxide, also known as selenious oxide, selenous oxide, or selenium(IV) oxide, is a chemical compound. Its chemical formula is SeO. It contains selenium in its +4 oxidation state. It also contains oxide ions. It is toxic.
Selenium dioxide is a white solid. It dissolves in water to make selenous acid. It easily evaporates. The vapor smells like horseradish sauce. It can burn the nose. It reacts with bases to make selenites.
Selenium dioxide can be made by burning selenium in air. It can also be made by reacting selenium with nitric acid or hydrogen peroxide. Another way to make it is to heat selenous acid.
Selenium dioxide is very rare as a mineral. It only is in places where coal caught on fire and the selenides were oxidized to selenium dioxide.
Selenium dioxide is used in making organic compounds. Selenium dioxide is used as a coloring in glass. Cobalt in glass makes a blue color. When a little selenium dioxide is added, the glass becomes colorless. When more selenium dioxide is added, the glass becomes ruby red.
Selenium dioxide can dissolve in water to make toxic selenium compounds. Swallowing any more than a very tiny amount can cause selenium poisoning. Selenium dioxide is a weak oxidizing agent and does not catch things on fire.
Selenium oxide
Selenium oxide may refer to either of these chemical compounds:
Selenium trioxide
Selenium trioxide, also known as selenium(VI) oxide and selenic oxide, is a chemical compound. Its chemical formula is SeO. It contains selenium in its +6 oxidation state. It also contains oxide ions.
Selenium trioxide is a white solid. It evaporates easily. It dissolves easily in water. It is not stable and breaks down to make selenium dioxide and oxygen when it is heated. It is a powerful oxidizing agent like all selenates. It dissolves in water to make selenic acid.
It can be made by reacting potassium selenate with sulfur dioxide. It can also be made by dehydrating (removing the water from) selenic acid with a strong dessicant, like phosphorus(V) oxide.
Selenide
Selenide is an ion. Its chemical formula is Se. Selenides are similar to sulfides. Selenides are reducing agents when pure. They are stronger reducing agents than sulfides. Selenide ores are the source of selenium. Selenides are normally mixed with sulfides. The selenide ion is unstable except in very basic conditions. Normally hydroselenide is made, which is HSe. In acidic conditions, hydrogen selenide gas is made.
Hydroselenide
Hydroselenide is an ion. Its chemical formula is HSe. Hydroselenides are normally made in neutral or slightly basic conditions. If it is very basic, selenides are made. If it is acidic, hydrogen selenide is made.
Hydrogen selenide
Hydrogen selenide, also known as hydroselenic acid, selenium hydride, or selane, is a chemical compound. Its chemical formula is HSe. It is an acid. It contains hydrogen and selenide ions.
Hydrogen selenide is a colorless gas that dissolves in water to make an acidic solution. It smells like rotten horseradish. It is very toxic. It burns easily, making selenium dioxide. It is similar to hydrogen sulfide, a gas that smells like rotten eggs. It is a strong reducing agent.
Hydrogen selenide can be made by hydrolysis of aluminium selenide. This reaction also makes aluminium hydroxide. It can be made by reacting hydrogen with powdered selenium at a high temperature.
It can be used to add selenide ion to organic compounds. It can also be used to make selenium by reacting it with sulfur dioxide. This makes selenium, sulfur, and water.
Aluminium selenide
Aluminium selenide, also known as aluminum selenide or aluminium(III) selenide, is a chemical compound. Its chemical formula is AlSe. It contains aluminium in its +3 oxidation state. It contains aluminium and selenide ions.
It reacts with water to make hydrogen selenide. It is a reducing agent and can burn to make aluminium oxide and selenium dioxide.
It is made by reacting selenium with aluminium powder at a high temperature.
It is used to make hydrogen selenide.
Sodium selenide
Sodium selenide is a chemical compound. Its chemical formula is NaSe. It contains sodium and selenide ions.
Sodium selenide is a solid. It reacts with water to make a mixture of sodium hydroxide and sodium hydroselenide. It is a reducing agent. It is oxidized to a mixture of selenide and selenium, making an offwhite color. It is eventually oxidized to selenium dioxide. it reacts with acids to make hydrogen selenide gas.
It is made by reacting selenium with a solution of sodium in liquid ammonia.
Sodium selenide is used to react with some organic compounds.
Selenium monochloride
Selenium monochloride, also known as selenium(I) chloride or diselenium dichloride, is a chemical compound. Its chemical formula is SeCl. It contains selenium in its +1 oxidation state. It also contains chloride ions.
It is a reddish brown oily liquid.
It can be made by reacting selenium, selenium dioxide, and hydrochloric acid. It can be made though by just reacting chlorine with selenium. Another way to make it is reacting oleum and hydrochloric acid with selenium.
It can be used to add selenium to other chemical compounds.
Selenite
Selenite is an ion. Its chemical formula is SeO. It makes the hydrogen selenite ion, HSeO in neutral conditions. When in acidic conditions it makes selenous acid. They are normally made by heating metal oxides with selenium dioxide. An example would be sodium selenite. Selenites are weak oxidizing agents.
Selenate
Selenate is an ion. Its chemical formula is SeO. They dissolve easily in water. They are strong oxidizing agents. In very acidic conditions, it makes selenic acid. Sodium selenate is an example.
Selenic acid
Selenic acid is a chemical compound. It is an acid. Its chemical formul is HSeO.
It is normally a colorless solution in water. It is a strong oxidizing agent. It can turn into selenium trioxide when dehydrated carefully. It is a very strong acid. It reacts with hydrochloric acid to make chlorine and selenous acid. It can dissolve gold to make gold selenate. When heated above 200°C, it releases oxygen and turns into selenous acid. It reacts with bases to make selenates.
Selenic acid is made by oxidation of selenium dioxide with hydrogen peroxide. It is hard to evaporate it, but when it is evaporated, it makes colorless crystals. It can be made by oxidation of selenous acid with a strong oxidizing agent, such as potassium permanganate, chlorine, or bromine. The HCl and HBr made as a byproduct can reduce the selenic acic to selenous acid again, though, so it has to be taken out.
It can also be made by reacting selenium with chlorine in water.
Selenous acid
Selenous acid, also known as selenious acid, is a chemical compound. Its chemical formula is HSeO. It is an acid. It contains hydrogen and selenite ions.
Selenous acid is a weak acid. It can be heated to make selenium dioxide. It is more stable than sulfurous acid. It can be crystallized as a white solid. It is a weak oxidizing agent. It reacts with bases to make selenites.
It is made by dissolving selenium dioxide in water.
It is used to dye steel a blue-grey color. It is used in the making of organic compounds.
Selenous acid is very toxic. Just ingesting a small amount can kill you.
Sodium selenate
Sodium selenate is a chemical compound. Its chemical formula is NaSeO. It contains sodium and selenate ions.