Mercury is special because it’s the only liquid metallic element at standard temperature and pressure. The symbol of mercury is Hg.
Physical properties of mercury
The density of mercury is really high. It’s significantly denser than most other metals, so for example a coin floats on the top of mercury. It’s melting point is around -39oC, so if we go below this, it’s going to freeze solid. As it warms back to room temperature it will start melting to become liquid. The boiling point is relatively low compared with other metals, it is equal to 360oC, that’s why mercury is purify by distillation.
Because of strong metallic bonding forces between mercury atoms, it has a really high surface tension, that’s why the surface of the mercury is drawn into itself in a way to minimize its surface area, ideally forming a sphere. In a big amounts the spheres are not noticeable, because the effect of gravity is much greater than the surface tension. However, for smaller volumes, the force of gravity gets less and less and eventually the effect of surface tension can take over.
Mercury also conducts electricity, because it’s a metal, and this property is used to make mercury based electrical switches.
Mercury doesn’t normally exist as a metal in nature, and it’s usually found in the form of mercury sulfide, which is commonly known as cinnabar. Mercury sulfide exists in two forms, where one is red and the other is black. The red one is the most common.
Both of the two forms of mercury sulfide can be converted to mercury metal, which is usually done by roasting it. With the strong heating, it is broken down into elemental mercury, which is distilled off and collected. Mercury sulphide is completely insoluble in pure water but it can be dissolved in strongly basic solutions of sodium sulfide. Then, elemental mercury can be leached out of the solution by adding aluminum foil. The mercury that forms sinks to the bottom, which can be collected and cleaned up.
Is Mercury toxic ?
In terms of toxicity, mercury metal isn’t that dangerous. This is mostly because the skin doesn’t absorb it very well, and also because it isn’t reactive. It might be surprising, but the most dangerous thing about mercury metal is actually the vapours. Vapours are normally invisible, but we can see them using some UV light. If it is breathed in, it can be absorbed through the lungs which is dangerous. However, small amounts are still not that bad.
Mercury can form organic and inorganic compounds, and this is where the real danger comes from. The organic ones are the form that most people are exposed to because they’re found in a lot of seafood. They are highly fat soluble, so they are absorbed through the skin as well as the digestive tract of the human. There is a lot of organic mercury compounds, dimethylmercury is an example. Inorganic mercury are less scary but also dangerous. They are soluble in water and their toxicity on this solubility. Some of them like mercury sulfide are practically insoluble. So they’re relatively safe to handle and touch. On the other hand mercuric chloride is highly soluble so it is very toxic.
Mercury is also dangerous because it tends to bioaccumulate, it likes to stick in the body, this means that a small amount could be toxic after a long period.
Previously, mercury were used as medicine to treat many diseases like syphilis, yellow fever and many others. But over the years, mercury-based pharmaceuticals have been replaced with much safer alternatives. However, there are still some that are used.
Industrially, mercury was used for a long time to make things like thermometers, batteries and fluorescent lights, or to chemically produce sodium hydroxide and chlorine gas. However, just like with medicine all of these uses have either been replaced already, or they will be replaced in the future.