Mercury is the only metal that is liquid under normal temperature and pressure conditions. Mercury is a poor heat conductor yet a good electrical conductor. Mercury has a distinct electron configuration that strongly resists electron removal, causing it to behave similarly to noble gas elements. This makes mercury useful in constructing electric circuits because all metals will conduct electricity until they reach their melting points, at which point they become inert and no longer conduct.
The most common use for mercury is in thermometers. When you read the temperature on a mercury thermometer, you are reading the temperature of something hot against the temperature of something cold, which causes the mercury to change position in its tube and record a new temperature. The second most common use for mercury is as a contact material in switchgear and circuit breakers. The advantage of using mercury is that it provides very low resistance when closed, which means less loss in power supplies that use it.
But even though it is a well-known material, mercury is also very toxic. If you come into contact with it, do not eat it, don't breathe it, and definitely not put it in your body. Even in small amounts, it can cause serious health problems or death.
There are alternative materials that can be used instead of mercury in these applications. For example, gold-plated steel is an effective replacement for mercury thermometers.
Mercury, as a result, forms weak bonds and is a liquid at ambient temperature. The more electrically charged particles are present in any material, the greater its ability to conduct electricity.
The best way to understand how electrons move through a metal like mercury is to think about water flow in a pipe. If you have ever turned on a faucet and seen how quickly it flows from being half full to completely empty, then you have seen how electrons flow through a metal. There are no holes or gaps in a metal wire such as copper that would allow other substances to enter or leave the circuit, so any contact a person makes with the wire will cause an electric current to flow.
As electrons move through the metal, they also tend to stay near their original position because there are other electrons present to avoid moving away from their friends. This means that if one part of the wire gets more electrons, another will soon follow and the wire will remain balanced.
Mercury is a good electrical conductor because it allows electrons to flow easily from place to place. When you connect two mercury wires together, the electrons immediately begin flowing and there is very little delay before they reach their destination.
Mercury is a silvery-white liquid metal that is heavy. It is a poor conductor of heat yet a good conductor of electricity when compared to other metals. This property makes mercury useful in thermometers and electrical switches. However, the high concentration of energy at any one point in mercury's body can cause it to break down oxygen molecules and produce toxic gases such as hydrogen fluoride and chlorine gas.
The heat conductivity of mercury is about 0.5 W/mK which is higher than most other elements. Its thermal conductivity increases as the temperature rises, so mercury is used as a standard for measuring heat transfer rates. Mercury's high heat capacity per unit mass allows it to retain this heat for a long time before it escapes into its surroundings. This is why mercury thermometers can stay stable for so long without damage from fluctuations in temperature.
At room temperature, 1 cm3 of mercury has a heat capacity of 4.18 J. The heat flow across 2 cm of mercury is therefore 582 W. This is not very much heat, and any device using mercury thermometers or thermostats will need external cooling to prevent them from getting too hot.