Mercury (Hg)

Mercury is a chemical element with atomic number 80 in the periodic table. Accounting for only 0.08 parts per million (ppm) of the Earth’s crust, element number 80 is a very rare occurrence in the Earth’s crust.

This post-transition metal is the only metal element that occurs in liquid form. It has two valence electrons and is one of the most toxic chemicals in Mendeleev’s system of elements.  

Chemical and Physical Properties of Mercury

Atomic number80
ColorA liquid silvery-white metal
Physical stateLiquid at room temperature
Half-lifeFrom 80(+400-40) milliseconds to 444 years
Melting point−38.829°C, −37.892°F, 234.321 K
Boiling point356.619°C, 673.914°F, 629.769 K
Van der Waals radius155 pm
Ionic radius1.02 (+2) Å
Atomic weight200.59
Most characteristic isotope202Hg
Electronic shell[Xe] 4f14 5d10 6s2
The energy of the first ionization1004.6 kJ.mol-1
The energy of the second ionization1796 kJ.mol-1
The energy of the third ionization3294 kJ.mol-1
Crystal StructureRhombohedral
Covalent Radius1.49 Å
Atomic Radius1.76 Å
Atomic Volume14.82 cm³/mol
Name OriginFrom the Roman god Mercury; Latin: hydrargyrus (liquid silver)
DiscovererKnown to the ancients
Oxydation States(2),1
UsesUsed in thermometers, barometers, batteries, electrical switches, and mercury-vapor lighting products.
DescriptionSoft gray metal that looks like lead.

With the periodic table symbol Hg, atomic number 80, atomic mass of 200.592 g.mol-1, and electron configuration [Xe] 4f145d106s2, mercury is a highly mobile liquid metal that reaches its boiling point at 356.619°C, 673.914°F, or 629.769 K, while the melting point is achieved at −38.829°C, −37.892°F, or 234.321 K. 

In comparison with the other metals, mercury is a poor conductor of heat, but an excellent conductor of electricity. It has an electronegativity of 2.00 according to Pauling, and mercury’s atomic radius is 155 pm, as determined per van der Waals. 

How Was Mercury Discovered?

The first records of this chemical element trace back to 1500 BC, when mercury was found in the Egyptian tombs. Around 3000 years ago, the Babylonians, the ancient Chinese, and the Romans were allegedly using the element in creams and ointments that they applied to the skin. This proved to have a poisonous effect, due to the dangerously high amounts of Hg that was mixed with other chemicals. 

The Tragic Discovery of Qin Shi Huang 

The Chinese emperor Qin Shi Huang was the first to detect the toxic effect of mercury, which at that time, was not yet recognized as a chemical element. The emperor was in search of a magic elixir that would give him eternal life. He believed in the existence of wizards and sages that lived more than 10.000 years as a result of consuming a cinnabar (mercury sulfide, HgS) potion. So, he started adding cinnabar to his honey-sweetened wine. Unfortunately, mercury poisoning led him to premature death rather than eternal life. 

De Lavoisier: Establishing Mercury as a Chemical Element

In the 18th century, the great French chemist Antoinne-Laurent de Lavoisier (1743 – 1794), one of the founders of modern chemistry,  contributed immensely to determining the chemical properties of mercury through scientific research. In the summer of 1774, de Lavoisier and the distinguished English chemist Joseph Priestley (1733 – 1976) observed the reaction of a heated mercury calx. 

When exposed to high temperatures, the substance emitted a gas which triggered a vigorous flame from the candle. Consequently, they came to the conclusion that pure air contributes to a greater flame, and labeled the gas that came out of the decomposing mercury calx as  ‘dephlogisticated air’. From this point, de Lavoisier developed further scientific evidence that put mercury amongst the other chemical elements on the list that he compiled. 

How Did Mercury Get Its Name?

The symbol Hg under which mercury is classified is derived from the Greek word hydrargyrum, meaning ‘liquid silver’. The other name used for this highly mobile and difficult to contain chemical is ‘quicksilver’, which perfectly describes the physical appearance of the liquid metal with a shiny silver color. 

The name of the element mercury is also associated with the Roman god Mercury (the messenger of the Gods) and the planet Mercury. This tiny planet’s mobility was associated with the element’s own mobility, so that mercury remained the name of this element even in modern times, which is a unique occurrence. 

Where Can You Find Mercury?

Mercury rarely occurs independently in nature. The cinnabar (mercury sulfite) is the most common ore from which mercury can be obtained. For this reason, the ore is first ground up and exposed to a temperature of about 1.076 degrees F (580 degrees Celsius) with added oxygen during the process of extraction.

This liquid metal also occurs in the vicinity of hot springs or volcanos. Spain and Italy are the leading countries in the world’s production of mercury. 

Mercury in Everyday Life

Cinnabar (or vermillion) was used by the Palaeolithic painters around 30,000 years ago. Since it releases a bright red pigment, vermillion was used for decorating caves in Spain and France.

Today, we use mercury for various purposes:

  • Manufacturing thermometers, barometers, and other scientific instruments. However, due to safety concerns, these types of instruments are being replaced with digital alternatives;
  • Mercury vapor is used in the production of compact fluorescent light bulbs; when a spark passes through mercury in a tube, it gives out a blue to ultraviolet light used in fluorescent lamps. This ultraviolet light has the ability to destroy germs;
  • As an electrical conductor, mercury is used in the electrical switches of thermostats and alarm clocks;
  • Mercury is used for gold extraction. Namely, mercury forms alloys, i.e. amalgams with gold, silver, zinc, and cadmium. When both mercury and gold are present in the amalgam, the liquid metal is used for the extraction of gold from rocks, as gold dissolves into mercury, making it easier for the two substances to be isolated  through the process of mercury distillation;
  • The organomercury compound thimerosal is used for manufacturing vaccines, contact lens solutions, tattoo ink, cosmetics, and dental preparations;
  • Other mercury applications include its use in pesticides, antifouling paints, batteries, etc. 

How Dangerous Is Mercury?

The elemental form of mercury and its compounds are considered to be highly toxic. Upon ingestion, consumption of mercury-contaminated food, or skin contact with the chemical, mercury poisoning may occur. 

What Are the Symptoms of Mercury Poisoning?

The affected individuals may experience the following symptoms, side effects, and conditions:

  • Breathing difficulty;
  • Strong headaches;
  • Metal taste in the mouth;
  • Muscle weakness and cramping;
  • Disturbed sleep cycles;
  • Damage of the kidneys, nerves, and liver;
  • Irritability;
  • Damage of the reproductive system;
  • Lack of coordination;
  • Blurred vision;
  • Speech impairment;
  • Death.

Environmental Effects of Mercury

According to the EPA (United States Environmental Protection Agency), fish naturally contain large levels of mercury. Hence, when they become food for bigger fish (like sharks), they themselves become even more saturated with mercury. Consuming those bigger fish may result in mercury poisoning.

When mercury vapor is emitted into the atmosphere, it remains in the air as a pollutant for a longer amount of time. This mainly occurs as a result of the mercury mining processes. In order to reduce these mercury emissions into the environment, EPA and the Argonne National Laboratory (ANL) devised the Gold Shop Mercury Capture System (MCS).

Isotopes of Mercury

The isotopes of mercury range from 170Hg to 216Hg. Among them, 202Hg is the most abundant mercury isotope. There are forty radioactive isotopes and seven stable forms of this chemical element. Having a half-life of 444 years, the 194Hg radioisotope is the longest living radioactive form of mercury. 

 abun­dancehalf-life (t1/2)modepro­duct 
194Hgsyn444 yε194Au 
195Hgsyn9.9 hε195Au 
197Hgsyn64.14 hε197Au 
203Hg      syn46.612 dβ 203Tl 

Source: Wikipedia

List of Mercury Compounds 

Mercury typically adopts the oxidation states +1 or +2, but sometimes it has a +4 oxidation state. It forms numerous compounds, such as metal alloys, salts, iodides, bromides, nitrates, sulphates, etc.

  • Mercury(II) Perchlorate
  • Mercury(II) Chlorate
  • Mercury(II) Oxide
  • Mercury(I) Chloride
  • Mercury(I) Nitrite
  • Mercury(I) Phosphate
  • Mercury(II) Phosphate
  • Mercury(II) Nitrate Monohydrate
  • Mercury(I) Carbonate
  • Mercury(II) Chloride
  • Mercury(I) Perchlorate
  • Mercury(I) Nitrate
  • Mercury(II) Nitride
  • Mercury(II) Bromate
  • Mercury(II) Acetate
  • Mercury(I) Sulfate
  • Mercury(II) Carbonate
  • Mercury(II) Hydroxide
  • Mercury(II) Hydrogen Carbonate
  • Mercury(I) Cyanide
  • Mercury(I) Hydrogen Carbonate
  • Mercury(I) Phosphide
  • Mercury(I) Dichromate
  • Mercury(I) Oxide
  • Mercury(I) Hydroxide
  • Mercury(II) Bromide
  • Mercury(I) Chromate
  • Mercury(I) Nitride
  • Mercury(I) Fluoride
  • Mercury(I) Peroxide
  • Mercury(I) Sulfide

5 Interesting Facts and Explanations

  1. Mercury’s density is thirteen times greater than that of water, and it’s the only metal found in a liquid aggregate state at room temperature. 
  2. Today, there are still some traditional Chinese medicines in use that contain high levels of mercury, despite the scientifically confirmed toxic effect of this liquid metal.
  3. Antoinne-Laurent de Lavoisier is the first chemist who classified mercury as a poisonous chemical element.
  4. Phlogiston is a superseded chemical theory that hypothesized the idea of a fire-inducing element called phlogiston being released during the combustion of combustible bodies.
  5. The Caloris Basin is the largest impact crater on the closest planet to the Sun, Mercury. 

The Story of the Planet Mercury

Many centuries ago, Mercury, Venus, Mars, Jupiter, and Saturn were the only planets visible to ancient astronomers without the help of a telescope. The ancient Sumerians, for instance, could observe the movements of these planets in the night sky and worshiped them as deities. The Romans, on the other hand, noticed that the smallest visible planet, Mercury, moved more quickly than the other planets in the solar system, which is why they named it after the swiftest messenger and god of trade in Roman mythology, Mercury. 

In fact, when it comes to its speed, the ancient civilizations were right even without the help of modern technology – this rocky planet completes its orbit around the sun in only 88 Earth days, while some of the other planets take many years to complete the same manoeuvre. 

In 1631, Thomas Harriott and Galileo Galilei had the opportunity to analyze the surface of this tiny planet through a telescope for the first time. With the progress of technology in modern times, space exploration became easier. So, in 1974, Mariner 10 became the first spacecraft to ever land on the innermost planet of our solar system.

The Mission of NASA’s Messenger 

Several decades later, in 2008, NASA’s MESSENGER orbiter (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) analyzed the planet’s surface by performing three flybys, thus making the closest approach to Mercury in history. The mission of the MESSENGER  spacecraft was to find answers to several issues:

  • Mercury’s high density;
  • The planet’s geological history;
  • To discover the nature of its magnetic field and the structure of its core;
  • To see whether it has ice at the poles;
  • To learn what causes the tenuous atmosphere on.

What Is Mercury Really Like?

According to NASA and the Johns Hopkins University Applied Physics Laboratory, Mercury’s surface temperature reaches 840 degrees Fahrenheit (450 degrees Celsius), due to its proximity to the Sun. Also, it’s only a bit larger in size than the Earth’s Moon. Mercury’s thin atmosphere is called the exosphere and it’s made up of oxygen (O2), sodium (Na), hydrogen (H2), helium (He), and potassium (K). The surface of this rocky planet is made up of great curved cliffs, i.e. lobate scarps pointing to a still warm core. 

Furthermore, NASA’s researchers discovered the presence of a magnetic field, which they believe indicates the existence of an iron core. They also presume that Mercury’s core is at least partially molten. The planet’s highest point is determined to be south of Mercury’s equator, while its lowest point is located in the Rachmaninoff basin. The photos taken by the MESSENGER spacecraft of Mercury’s surface also show water ice contained in the craters located at the planet’s north pole.

Despite having only one percent of the pull of Earth’s magnetic core, Mercury’s core shows great activity. The charged particles that stream off the sun create the solar wind that generates  powerful magnetic tornadoes when it comes into contact with the magnetic field of the planet. 

The transit of Mercury in front of the face of the Sun occurs thirteen times in a century. In addition, it’s been estimated that a solar day on the planet with no rings or moons lasts approximately 176 Earth days.