Instruct: Given a question, retrieve documents that can help answer the question.
Query: What is the origin of the symbol Hg for mercury?
Mercury is a chemical element with symbol Hg and atomic number 80. It is commonly known as quicksilver and was formerly named hydrargyrum (/haɪˈdrɑːrdʒərəm/ hy-DRAR-jər-əm).[4] A heavy, silvery d-block element, mercury is the only metallic element that is liquid at standard conditions for temperature and pressure; the only other element that is liquid under these conditions is bromine, though metals such as caesium, gallium, and rubidium melt just above room temperature.
Hg is the chemical symbol of Mercury.
Hg or methyl-Hg (out) → Hg or methyl-Hg (in)
When α-HgS is used as a red pigment, it is known as vermilion. The tendency of vermilion to darken has been ascribed to conversion from red α-HgS to black β-HgS. However β-HgS was not detected at excavations in Pompeii, where originally red walls darkened, and was attributed to the formation of Hg-Cl compounds (e.g., corderoite, calomel, and terlinguaite) and calcium sulfate, gypsum.
The Hg–Hg bond length of 253 pm (Hg–Hg in the metal is 300 pm) and the Hg–Cl bond length in the linear HgCl unit is 243 pm. The overall coordination of each Hg atom is octahedral as, in addition to the two nearest neighbours, there are four other Cl atoms at 321 pm. Longer mercury polycations exist.
One may also note that the stable compound , recently synthesized, was found to consist of two-dimensional polymeric cations [–(S–)–Hg–Hg–(S–Hg–)–Hg– balanced by one-dimensional polymeric anions [––. In the cations, the sulfur atoms are trivalent, and the mercury atoms are divalent. In each unit, two of the mercury atoms form S–Hg–S bridges, while the other two form an S–Hg–Hg–S bridge.
β-HgS is precipitated as a black powder when HS is bubbled through solutions of Hg(II) salts. β-HgS is unreactive to all but concentrated acids. Mercury metal is produced from the cinnabar ore by roasting in air and condensing the vapour.
The essential trace element selenium (Se) is an antidote to mercury (Hg) and should according to Geir Bjørklund always be used in the treatment of mercury intoxication. The following is an excerpt from the abstract of a review by Bjørklund and collaborators (2017) about molecular interaction between Hg and Se: "Mercury and Se form stable coordination compounds, and Hg species are characterized by higher affinity to selenol groups as compared to thiol groups. Therefore, Se-containing molecules are targets for Hg binding that may at least partially mediate the biological outcome of Hg-Se interaction. Molecular interaction between these elements also involves mutual interaction between Hg and various selenoproteins. Experimental data demonstrate that Se treatment modifies brain Hg retention, modulates neurotoxicity and oxidative stress in the nervous tissue of animals. Human data also indicate that molecular interaction between Hg and Se may have a significant influence on neurodevelopment, brain functioning, and neurodegeneration. It is hypothesized that the effectiveness of Se protection against Hg neurotoxicity may be determined by the dose of elements as well as their particular chemical forms".
The crystal structure of mercurous sulfate is made up of Hg dumbbells and SO anions as main building units. Hg dumbbell is surrounded by four Oxygen atoms with Hg₋O distance ranging from 2.23 to 2.93 Å, whereas Hg-Hg distance is approximately 2.500Å.
Studies have shown mercury(I) sulfate to have the mercury atoms arranged in doublets with a bond distance of 2.500Å. The metal atom doublets are oriented parallel to the an axis in a unit cell. Mercury doublets form part of infinite chain SO - Hg - Hg - SO - Hg - Hg - … The Hg - Hg - O bond angle is 165°±1 . The chain crosses the unit cell diagonally. The mercury sulfate structure is held together by weak Hg-O interactions. The SO does not act as a single anion, but rather coordinated to the mercury metal.
Only the mercury isotope Hg, which occurs with a frequency of 0.15% in natural mercury, can be converted to gold by slow neutron capture, and following electron capture, decay into gold's only stable isotope, Au. When other mercury isotopes are irradiated with slow neutrons, they also undergo neutron capture, but either convert into each other or beta decay into the thallium isotopes Tl and Tl.
Using fast neutrons, the mercury isotope Hg, which composes 9.97% of natural mercury, can be converted by splitting off a neutron and becoming Hg, which then decays into stable gold. This reaction, however, possesses a smaller activation cross-section and is feasible only with unmoderated reactors.
MerR forms a stable trigonal planar complex with Hg, which causes it to be released much later than when mercury(II) reductase has reduced all free Hg in the cytoplasm. Thus, it causes an excess in production of mercuric(II) reductase. To circumvent this problem, MerD also binds to MerO in order to act antagonistically to Hg bound MerR. MerD is produced when MerR is active with Hg since MerD is encoded in the structural mer genes.
Mercurial's major design goals include high performance and scalability, decentralization, fully distributed collaborative development, robust handling of both plain text and binary files, and advanced branching and merging capabilities, while remaining conceptually simple. It includes an integrated web-interface. Mercurial has also taken steps to ease the transition for users of other version control systems, particularly Subversion. Mercurial is primarily a command-line driven program, but graphical user interface extensions are available, e.g. TortoiseHg, and several IDEs offer support for version control with Mercurial. All of Mercurial's operations are invoked as arguments to its driver program codice_1 (a reference to Hg - the chemical symbol of the element mercury).
In common with other Hg(I) (mercurous) compounds which contain linear X-Hg-Hg-X units, HgI contains linear IHgI units with an Hg-Hg bond length of 272 pm (Hg-Hg in the metal is 300 pm) and an Hg-I bond length of 268 pm. The overall coordination of each Hg atom is octahedral as it has in addition to the two nearest neighbours there are four other I atoms at 351 pm. The compound is often formulated as Hg 2I.
In common with other Hg(I) (mercurous) compounds which contain linear X-Hg-Hg-X units, HgF contains linear FHgF units with an Hg-Hg bond length of 251 pm (Hg-Hg in the metal is 300 pm) and an Hg-F bond length of 214 pm. The overall coordination of each Hg atom is a distorted octahedron; in addition to the bonded F and other Hg of the molecule, there are four other F atoms at 272 pm. The compound is often formulated as Hg 2F.
Mercury (Hg) is a liquid down to −39°C (see Melting Point (m.p.)). Bonding forces are weaker for Hg–Hg bonds than for its immediate neighbors such as cadmium (m.p. 321°C) and gold (m.p. 1064°C). The lanthanide contraction is a partial explanation; however, it does not entirely account for this anomaly. In the gas phase mercury is alone in metals in that it is quite typically found in a monomeric form as Hg(g). Hg(g) also forms and it is a stable species due to the relativistic shortening of the bond.
Most natural mercury occurs as cinnabar, HgS. Here mercury (Hg) is bound very tightly to sulfur, but weathering slowly releases the mercury to the environment. There are also trace amounts of mercury in coal. Mining mercury or burning coal results in releasing mercury. Volcanoes and forest fires are also sources of mercury.
Bis(trimethylsilyl)mercury (CH)Si-Hg-Si(CH) reacts with chloro-iminium and chloro-amidinium salts to give a metal-free carbene and elemental mercury. For example, (CH)Si-Hg-Si(CH) + RN=C(Cl)-NRCl → RN-C:-NR + Hg + (CH)Si-Cl
The structural formula is supposed to contain two mercury atoms bound to each other, as in the real compound mercury(I) chloride (calumel), . The latter is an ionic compound with the dimercury(I) cation, or Hg–Hg, and chloride anions . 
There are seven stable isotopes of mercury (Hg) with Hg being the most abundant (29.86%). The longest-lived radioisotopes are Hg with a half-life of 444 years, and Hg with a half-life of 46.612 days. Most of the remaining 32 radioisotopes have half-lives that are less than a day. Hg and Hg are the most often studied NMR-active nuclei, having spin quantum numbers of 1/2 and 3/2 respectively.
Mercury(II) acetate is a crystalline solid consisting of isolated Hg(OAc) molecules with Hg-O distances of 2.07 Å. Three long, weak intermolecular Hg···O bonds of about 2.75 Å are also present, resulting in a slightly distorted square pyramidal coordination geometry at Hg.
The substrates used in mercuric(II) reductase, as shown above, are Hg and NADPH. In the catalytic active site of the enzyme, Hg is held as a complex with two cysteine thiolates in a linear geometry. NADPH from the cytoplasm of the cell undergo a hydride transfer with an embedded FAD forming FADH. The resulting FADH then reduces Hg into Hg, in turn being oxidized back into FAD. After reduction, the mercury is then released from the enzyme as a volatile vapour.
There are seven stable isotopes of mercury with 202 Hg being the most abundant (29.86%). The longest-lived radioisotopes are 194 Hg with a half-life of 444 years, and 203 Hg with a half-life of 46.612 days. Most of the remaining radioisotopes have half-lives that are less than a day. 199 Hg and 201 Hg are the most often studied NMR-active nuclei, having spins of ​1⁄2 and ​3⁄2 respectively.[5]
Hg is the modern chemical symbol for mercury. It comes from hydrargyrum, a Latinized form of the Greek word ὑδράργυρος (hydrargyros), which is a compound word meaning "water-silver" (from ὑδρ- hydr-, the root of ὕδωρ, "water," and ἄργυρος argyros "silver") – since it is liquid like water and shiny like silver. The element was named after the Roman god Mercury, known for his speed and mobility. It is associated with the planet Mercury; the astrological symbol for the planet is also one of the alchemical symbols for the metal; the Sanskrit word for alchemy is Rasavātam which means "the way of mercury".[15] Mercury is the only metal for which the alchemical planetary name became the common name.[16]
A millimetre of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high, and currently defined as exactly pascals. It is denoted by the symbol mmHg or mm Hg.
Unlike its lighter neighbors, cadmium and zinc, mercury usually forms simple stable compounds with metal-metal bonds. Most mercury(I) compounds are diamagnetic and feature the dimeric cation, Hg2+ 2. Stable derivatives include the chloride and nitrate. Treatment of Hg(I) compounds complexation with strong ligands such as sulfide, cyanide, etc. induces disproportionation to Hg2+ and elemental mercury.[41] Mercury(I) chloride, a colorless solid also known as calomel, is really the compound with the formula Hg2Cl2, with the connectivity Cl-Hg-Hg-Cl. It is a standard in electrochemistry. It reacts with chlorine to give mercuric chloride, which resists further oxidation. Mercury(I) hydride, a colorless gas, has the formula HgH, containing no Hg-Hg bond.