No one has the credit for finding mercury. It was found in ancient history. Mercury was found in Egyptian tombs that are from 1500 BC. Chinese people also knew it from long ago. In China and Tibet, people thought using mercury would make them live longer and have better health. One of China's emperors, Qín Shǐ Huáng Dì, is said to have been buried in a tomb with rivers of flowing mercury. He was killed by drinking a mixture of mercury and powdered jade because he wanted to live forever. However, this only made him die of liver failure, poisoning, and brain death. The ancient Greeks used mercury in ointments. The Egyptians and the Romans used it in cosmetics. These cosmetics sometimes hurt and made faces uglier.
Mercury is a silvery-white liquid post-transition metal. The reason for mercury being a liquid is quite complex. It is quite heavy; a chunk of iron can float on mercury. Compared to other metals, it does not conduct heat well. However, it conducts electricity fairly well. Mercury is the only metal with a known melting point (−38.83 °C) lower than caesium. Mercury is one of the two elements that are liquids at room temperature and normal pressure. Bromine is the other one.
Mercury may be seen as a transition metal, but it is normally seen as a post-transition metal. It is in Group 12 of the periodic table. Mercury has seven stable (nonradioactive) isotopes. 202Hg is the most common isotope. Mercury makes a blue to ultraviolet color in a tube when a spark is passed through it. The ultraviolet light can kill germs.
Mercury is an unreactive metal. It does not corrode in air unless hydrogen sulfide is also there, similar to silver. Mercury can oxidize to mercury(II) oxide when heated in air. If it is heated further, it decomposes into mercury and oxygen again. It does not dissolve in ordinary acids, but can dissolve in oxidizing acids to make mercury salts. It can make amalgams when mixed with most metals, like aluminium, gold, and zinc. Iron, tantalum, tungsten, and platinum do not make amalgams with mercury. Iron flasks were used to trade mercury because of this.
Mercury can dissolve large amounts of aluminium metal, making it dangerous to transport in aluminium containers. The thin layer of oxide on aluminium stops it from amalgamating (making an amalgam with) aluminium, but the oxide coating can be damaged to expose the metal. Then the aluminium metal is dissolved and oxidizes to aluminium oxide. The aluminium oxide forms a solid and releases the mercury, which amalgamates more aluminium. This process keeps repeating until a large amount of aluminium is dissolved.
Mercury forms chemical compounds in 2 oxidation states: +1 and +2. Mercury(I) compounds are weak oxidizing agents and weak reducing agents. Most of them are colorless. They easily disproportionate to mercury(II) compounds and mercury metal. They react with oxygen in the air to make mercury(II) compounds. Many mercury(I) compounds do not dissolve in water. Mercury(I) chloride is one of the most common mercury(I) compounds. Mercury(II) compounds are strong oxidizing agents and very corrosive. Mercury(II) compounds are red, yellow, or colorless. Mercury(II) oxide and mercury(II) chloride are the most common mercury(II) compounds in the laboratory.
One thing they have in common is that they are all toxic. The soluble ones are more toxic than the insoluble ones.
Also known as mercurous compounds, these are weak reducing agents and weak oxidizing agents. Most of them do not dissolve in water, making them less toxic than mercury(II) compounds. Most of them are colorless or yellow.
- Mercury(I) bromide, insouble white solid
- Mercury(I) chloride, calomel, insoluble, white
- Mercury(I) fluoride, light yellow
- Mercury(I) iodide, a little soluble, unstable, yellow
- Mercury(I) nitrate, very slightly soluble, white
- Mercury(I) sulfate, light yellow solid
Also known as mercuric compounds, these are strong oxidizing agents. Most of them dissolve in water, making them very toxic. They are colorless or red.
- Mercury(II) bromide, white solid
- Mercury(II) chloride, white solid, corrosive sublimate
- Mercury(II) fluoride, white solid
- Mercury(II) iodide, somewhat soluble, bright red
- Mercury(II) oxide, orange, yellow or red, does not dissolve in water like most oxides
- Mercury(II) nitrate, soluble, white, used to make hats
- Mercury(II) sulfate, white solid
- Mercury(II) sulfide, red solid
These contain mercury reacted with a organic molecule. They are even more toxic than other mercury compounds since they get absorbed very easily.
- Dimethylmercury, colorless, extremely toxic liquid
Mercury is a rare metal. It is about as common as silver. Mercury is not expensive like silver because the mercury is very easy to get from the places where it is found. Mercury can be found in elemental (liquid) form in nature, but this is not common. Mercury as an element is the only liquid that is recognized as a mineral by the International Mineralogical Association. It is most often found in the form of cinnabar, a mercury(II) sulfide mineral. The biggest deposits of cinnabar used to be found in Spain, but now are found in China. It also occurs in other minerals like calomel, a mercury(I) chloride mineral.
China and Kyrgyzstan are the two main makers of mercury. Mines in Italy, the United States, and Mexico have been closed. China is opening more mines because the European Union wants to use fluorescent lights, which need mercury.
Uses of mercury
- In cosmetics, (thiomersal is widely used to make mascara.)
- As a liquid electrolyte in a variant of the chloralkali process.
- In mining, especially of gold and silver.
- In mercury-vapor lamps and fluorescent lamps.
- Certain thermometers, barometers and manometers. Because of its toxicity, it can be replaced by alcohol for most of these uses.
- Certain electrical switches that turn on or off when tilted.
Mercury is liquid at room temperature, and fumes of mercury are very poisonous. Ingested elemental mercury is less dangerous. The biggest problems are organic mercury compounds which are eaten with food. However, inorganic compounds such as mercury(II) nitrate are also highly toxic by ingestion (eating) or inhalation (breathing in) of the dust. Mercury can cause both chronic and acute poisoning.
In the year 1810, over 200 people died of mercury poisoning on the ship Triumph because a barrel of mercury had leaked.
Mercury is extremely poisonous and has to be used carefully. When mercury is spilled, there are special ways to clean it up. Smaller drops should be combined to a larger drop on hard surfaces to be removed more easily (for example, being pushed into a bag that can be thrown away). Vacuum cleaners and brooms should not be used. This is because they can spread mercury even more. Afterwards, elements such as sulfur or zinc powder should be sprinkled over the place, then collected and cleaned away. It is not easy to clean mercury entirely off clothing, so it is better not to use them anymore. Breathing in mercury vapor is also very dangerous.
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Mercury (element) Facts for Kids. Kiddle Encyclopedia.