Hydrogen chalcogenide

Last updated
Water, hydrogen sulfide, and hydrogen selenide, three simple hydrogen chalcogenides

Hydrogen chalcogenides (also chalcogen hydrides or hydrogen chalcides) are binary compounds of hydrogen with chalcogen atoms (elements of group 16: oxygen, sulfur, selenium, tellurium, polonium, and livermorium). Water, the first chemical compound in this series, contains one oxygen atom and two hydrogen atoms, and is the most common compound on the Earth's surface. [1]


Dihydrogen chalcogenides

The most important series, including water, has the chemical formula H2X, with X representing any chalcogen. They are therefore triatomic. They take on a bent structure and as such are polar molecules. Water is an essential compound to life on Earth today, [2] covering 70.9% of the planet's surface. The other hydrogen chalcogenides are usually extremely toxic, and have strong unpleasant scents usually resembling rotting eggs or vegetables. Hydrogen sulfide is a common product of decomposition in oxygen-poor environments and as such is one chemical responsible for the smell of flatulence. It is also a volcanic gas. Despite its toxicity, the human body intentionally produces it in small quantities for use as a signaling molecule.

Water can dissolve the other hydrogen chalcogenides (at least those up to hydrogen telluride), forming acidic solutions known as hydrochalcogenic acids. Although these are weaker acids than the hydrohalic acids, they follow a similar trend of acid strength increasing with heavier chalcogens, and also form in a similar way (turning the water into a hydronium ion H3O+ and the solute into a XH ion). It is unknown if polonium hydride forms an acidic solution in water like its lighter homologues, or if it behaves more like a metal hydride (see also hydrogen astatide).

CompoundAs aqueous solution Chemical formula Geometry pKa model
hydrogen oxide
oxygen hydride
water H2O H2O 2D labelled.svg 13.995 Water molecule 3D.svg
hydrogen sulfide
sulfur hydride
hydrosulfuric acid H2S Hydrogen-sulfide-2D-dimensions.svg 7.0 Hydrogen-sulfide-3D-vdW.svg
hydrogen selenide
selenium hydride
hydroselenic acid H2Se Hydrogen-selenide-2D-dimensions.svg 3.89 Hydrogen-selenide-3D-vdW.svg
hydrogen telluride
tellurium hydride
hydrotelluric acid H2Te Hydrogen-telluride-2D-dimensions.svg 2.6 Hydrogen-telluride-3D-vdW.svg
hydrogen polonide
polonium hydride
hydropolonic acid H2Po Poloniumwasserstoff.svg  ? Polonium-hydride-3D-vdW.svg
hydrogen livermoride
livermorium hydride
hydrolivermoric acidH2Lv ? Livermorium-hydride-3D-balls.png

Some properties of the hydrogen chalcogenides follow: [3]

Melting point (°C)0.0−85.6−65.7−51−35.3
Boiling point (°C)100.0−60.3−41.3−436.1
−285.9+20.1+73.0+99.6 ?
Bond angle (H–X–H) (gas)104.45°92.1°91°90°90.9° (predicted) [4]
Dissociation constant (HX, K1)1.8 × 10−161.3 × 10−71.3 × 10−42.3 × 10−3 ?
Dissociation constant (X2−, K2)07.1 × 10−151 × 10−111.6 × 10−11 ?
Comparison of the boiling points of the hydrogen chalcogenides and hydrogen halides; it can be seen that hydrogen fluoride similarly exhibits anomalous effects due to hydrogen bonding. Ammonia also misbehaves similarly. Boiling-points Chalcogen-Halogen.svg
Comparison of the boiling points of the hydrogen chalcogenides and hydrogen halides; it can be seen that hydrogen fluoride similarly exhibits anomalous effects due to hydrogen bonding. Ammonia also misbehaves similarly.
Comparison of the melting (blue) and boiling (red) points of the hydrogen chalcogenides. The blue and red lines are least sqares fits for the non-oxygen chalcogenides, showing water should melt at -88 degC and boil at -75 degC. Mp and bp of H2E (E=O,S,Se,Te,Po) Celsius vs atomic number.svg
Comparison of the melting (blue) and boiling (red) points of the hydrogen chalcogenides. The blue and red lines are least sqares fits for the non-oxygen chalcogenides, showing water should melt at -88 °C and boil at -75 °C.

Many of the anomalous properties of water compared to the rest of the hydrogen chalcogenides may be attributed to significant hydrogen bonding between hydrogen and oxygen atoms. Some of these properties are the high melting and boiling points (it is a liquid at room temperature), as well as the high dielectric constant and observable ionic dissociation. Hydrogen bonding in water also results in large values of heat and entropy of vaporisation, surface tension, and viscosity. [5]

The other hydrogen chalcogenides are highly toxic, malodorous gases. Hydrogen sulfide occurs commonly in nature and its properties compared with water reveal a lack of any significant hydrogen bonding. [6] Since they are both gases at STP, hydrogen can be simply burned in the presence of oxygen to form water in a highly exothermic reaction; such a test can be used in beginner chemistry to test for the gases produced by a reaction as hydrogen will burn with a pop. Water, hydrogen sulfide, and hydrogen selenide may be made by heating their constituent elements together above 350 °C, but hydrogen telluride and polonium hydride are not attainable by this method due to their thermal instability; hydrogen telluride decomposes in moisture, in light, and in temperatures above 0 °C. Polonium hydride is unstable, and due to the intense radioactivity of polonium (resulting in self-radiolysis upon formation), only trace quantities may be obtained by treating dilute hydrochloric acid with polonium-plated magnesium foil. Its properties are somewhat distinct from the rest of the hydrogen chalcogenides, since polonium is a metal while the other chalcogens are not, and hence this compound is intermediate between a normal hydrogen chalcogenide or hydrogen halide such as hydrogen chloride, and a metal hydride like stannane. Like water, the first of the group, polonium hydride is also a liquid at room temperature. Unlike water, however, the strong intermolecular attractions that cause the higher boiling point are van der Waals interactions, an effect of the large electron clouds of polonium. [3]

Dihydrogen dichalcogenides

Dihydrogen dichalcogenides have the chemical formula H2X2, and are generally less stable than the monochalcogenides, commonly decomposing into the monochalcogenide and the chalcogen involved.

The most important of these is hydrogen peroxide, H2O2, a pale blue, nearly colourless liquid that has a lower volatility than water and a higher density and viscosity. It is important chemically as it can be either oxidised or reduced in solutions of any pH, can readily form peroxometal complexes and peroxoacid complexes, as well as undergoing many proton acid/base reactions. In its less concentrated form hydrogen peroxide has some major household uses, such as a disinfectant or for bleaching hair; much more concentrated solutions are much more dangerous.

Compound Chemical formula Bond lengthModel
hydrogen peroxide
hydrogen disulfide
Hydrogen disulfide bonds.png
hydrogen diselenide [7]
hydrogen ditelluride [8]

Some properties of the hydrogen dichalcogenides follow:

Melting point (°C)-0.43−89.6 ? ?
Boiling point (°C)150.2 (decomposes)70.7 ? ?

An alternative structural isomer of the dichalcogenides, in which both hydrogen atoms are bonded to the same chalcogen atom, which is also bonded to the other chalcogen atom, have been examined computationally. These H2X+–X structures are ylides. This isomeric form of hydrogen peroxide, oxywater, has not been synthesized experimentally. The analogous isomer of hydrogen disulfide, thiosulfoxide, has been detected by mass spectrometry experiments. [9]

It is possible for two different chalcogen atoms to share a dichalcogenide, as in hydrogen thioperoxide (H2SO); more well-known compounds of similar description include sulfuric acid (H2SO4).

Higher dihydrogen chalcogenides

All straight-chain hydrogen chalcogenides follow the formula H2Xn.

Higher hydrogen polyoxides than H2O2 are not stable. [10] Trioxidane, with three oxygen atoms, is a transient unstable intermediate in several reactions. The next two in the oxygen series, tetraoxidane and pentaoxidane, have also been synthesized and found to be highly reactive. An alternative structural isomer of trioxidane, in which the two hydrogen atoms are attached to the central oxygen of the three-oxygen chain rather than one on each end, has been examined computationally. [11]

Beyond H2S and H2S2, many higher polysulfanes H2Sn (n = 3–8) are known as stable compounds. [12] They feature unbranched sulfur chains, reflecting sulfur's tendency for catenation. Starting with H2S2, all known polysulfanes are liquids at room temperature. H2S2 is colourless while the other polysulfanes are yellow; the colour becomes richer as n increases, as do the density, viscosity, and boiling point. A table of physical properties is given below. [13]

Compound Density at 20 °C (g·cm−3) Vapour pressure (mmHg)Extrapolated boiling point (°C)
H2S1.363 (g·dm−3)1740 (kPa, 21 °C)−60

However, they can easily be oxidised and are all thermally unstable, disproportionating readily to sulfur and hydrogen sulfide, a reaction for which alkali acts as a catalyst: [13]

8 H2Sn → 8 H2S + (n − 1) S8

They also react with sulfite and cyanide to produce thiosulfate and thiocyanate respectively. [13]

An alternative structural isomer of the trisulfide, in which the two hydrogen atoms are attached to the central sulfur of the three-sulfur chain rather than one on each end, has been examined computationally. [11] Thiosulfurous acid, a branched isomer of the tetrasulfide, in which the fourth sulfur is bonded to the central sulfur of a linear dihydrogen trisulfide structure ((HS)2S+−S), has also been examined computationally. [14] Thiosulfuric acid, in which two sulfur atoms branch off of the central of a linear dihydrogen trisulfide structure has been studied computationally as well. [15]

Higher polonium hydrides may exist. [16]

Other hydrogen-chalcogen compounds

Heavy water Heavy-water-3D-vdW.svg
Heavy water

Some monohydrogen chalcogenide compounds do exist and others have been studied theoretically. As radical compounds, they are quite unstable. The two simplest are hydroxyl (HO) and hydroperoxyl (HO2). The compound hydrogen ozonide (HO3) is also known, [17] along with some of its alkali metal ozonide salts are (various MO3). [18] The respective sulfur analogue for hydroxyl is sulfanyl (HS) and HS2 for hydroperoxyl.


One or both of the protium atoms in water can be substituted with the isotope deuterium, yielding respectively semiheavy water and heavy water, the latter being one of the most famous deuterium compounds. Due to the high difference in density between deuterium and regular protium, heavy water exhibits many anomalous properties. The radioisotope tritium can also form tritiated water in much the same way. Another notable deuterium chalcogenide is deuterium disulfide. Deuterium telluride (D2Te) has slightly higher thermal stability than protium telluride, and has been used experimentally for chemical deposition methods of telluride-based thin films. [19]

Hydrogen shares many properties with the halogens; substituting the hydrogen with halogens can result in chalcogen halide compounds such as oxygen difluoride and dichlorine monoxide, alongside ones that may be impossible with hydrogen such as chlorine dioxide.

Hydrogen Ions

One of the most well-known hydrogen chalcogenide ions is the hydroxide ion, and the related hydroxy functional group. The former is present in alkali metal, alkaline earth, and rare-earth hydroxides, formed by reacting the respective metal with water. The hydroxy group appears commonly in organic chemistry, such as within alcohols. The related bisulfide/sulfhydryl group appears in hydrosulfide salts and thiols, respectively.

The hydronium (H3O+) ion is present in aqueous acidic solutions, including the hydrochalcogenic acids themselves, as well as pure water alongside hydroxide.

Related Research Articles

<span class="mw-page-title-main">Chalcogen</span> Group of chemical elements

The chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioactive elements polonium (Po) and livermorium (Lv). Often, oxygen is treated separately from the other chalcogens, sometimes even excluded from the scope of the term "chalcogen" altogether, due to its very different chemical behavior from sulfur, selenium, tellurium, and polonium. The word "chalcogen" is derived from a combination of the Greek word khalkόs (χαλκός) principally meaning copper, and the Latinized Greek word genēs, meaning born or produced.

<span class="mw-page-title-main">Functional group</span> Group of atoms giving a molecule characteristic properties

In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest of the molecule's composition. This enables systematic prediction of chemical reactions and behavior of chemical compounds and the design of chemical synthesis. The reactivity of a functional group can be modified by other functional groups nearby. Functional group interconversion can be used in retrosynthetic analysis to plan organic synthesis.

<span class="mw-page-title-main">Hydride</span> Molecule with a hydrogen bound to a more electropositive element or group

In chemistry, a hydride is formally the anion of hydrogen (H), a hydrogen atom with two electrons. The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are also called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride of nitrogen, etc. For inorganic chemists, hydrides refer to compounds and ions in which hydrogen is covalently attached to a less electronegative element. In such cases, the H centre has nucleophilic character, which contrasts with the protic character of acids. The hydride anion is very rarely observed.

<span class="mw-page-title-main">Chalcogenide</span>

A chalcogenide is a chemical compound consisting of at least one chalcogen anion and at least one more electropositive element. Although all group 16 elements of the periodic table are defined as chalcogens, the term chalcogenide is more commonly reserved for sulfides, selenides, tellurides, and polonides, rather than oxides. Many metal ores exist as chalcogenides. Photoconductive chalcogenide glasses are used in xerography. Some pigments and catalysts are also based on chalcogenides. The metal dichalcogenide MoS2 is a common solid lubricant.

An oxyacid, oxoacid, or ternary acid is an acid that contains oxygen. Specifically, it is a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen atom bonded to oxygen that can dissociate to produce the H+ cation and the anion of the acid.

A polysulfane is a chemical compound of formula H2Sn, where n > 1. Compounds containing 2 – 8 sulfur atoms have been isolated, longer chain compounds have been detected, but only in solution. H2S2 is colourless, higher members are yellow with the colour increasing with the sulfur content. In the chemical literature the term polysulfanes is sometimes used for compounds containing −(S)n, e.g. organic polysulfanes R1−(S)n−R2.

Thiosulfuric acid is the inorganic compound with the formula H2S2O3. It has attracted academic interest as a simple, easily accessed compound that is labile. It has few practical uses.

Zinc compounds are chemical compounds containing the element zinc which is a member of the group 12 of the periodic table. The oxidation state of zinc in most compounds is the group oxidation state of +2. Zinc may be classified as a post-transition main group element with zinc(II). Zinc compounds are noteworthy for their nondescript appearance and behavior: they are generally colorless, do not readily engage in redox reactions, and generally adopt symmetrical structures.

<span class="mw-page-title-main">Hydrogen disulfide</span> Chemical compound

Hydrogen disulfide is the inorganic compound with the formula H2S2. This hydrogen chalcogenide is a pale yellow volatile liquid with a camphor-like odor. It decomposes readily to hydrogen sulfide and elemental sulfur.

Gold chalcogenides are compounds formed between gold and one of the chalcogens, elements from group 16 of the periodic table: oxygen, sulfur, selenium, or tellurium.

<span class="mw-page-title-main">Properties of water</span> Physical and chemical properties of pure water

Water is a polar inorganic compound that is at room temperature a tasteless and odorless liquid, which is nearly colorless apart from an inherent hint of blue. It is by far the most studied chemical compound and is described as the "universal solvent" and the "solvent of life". It is the most abundant substance on the surface of Earth and the only common substance to exist as a solid, liquid, and gas on Earth's surface. It is also the third most abundant molecule in the universe.

<span class="mw-page-title-main">Polonium hydride</span> Chemical compound

Polonium hydride (also known as polonium dihydride, hydrogen polonide, or polane) is a chemical compound with the formula PoH2. It is a liquid at room temperature, the second hydrogen chalcogenide with this property after water. It is very unstable chemically and tends to decompose into elemental polonium and hydrogen. It is a volatile and very labile compound, from which many polonides can be derived. Additionally, it is radioactive.

The chalcogens react with each other to form interchalcogen compounds.

<span class="mw-page-title-main">Thiosulfurous acid</span> Chemical compound

Thiosulfurous acid is a hypothetical chemical compound with the formula HS−S(=O)−OH or HO−S(=S)−OH. Attempted synthesis leads to polymers. It is a low oxidation state (+1) sulfur acid. It is the Arrhenius acid for disulfur monoxide. Salts derived from thiosulfurous acid, which are also unknown, are named "thiosulfites" or "sulfurothioites". The ion is S=SO2−

Hydrogen thioperoxide, also called oxadisulfane or sulfanol, is the chemical with the structure H–S–O–H. It can be considered as the simple sulfur-substituted analog of the common hydrogen peroxide (H–O–O–H) chemical, and as the simplest hydrogen chalcogenide containing more than one type of chalcogen. The chemical has been described as the "missing link" between hydrogen peroxide and hydrogen disulfide (H–S–S–H), though it is substantially less stable than either of the other two. It is the inorganic parent structure of the sulfenic acid class of organic compounds (R–S–O–H) and also the oxadisulfide linkage (R1–S–O–R2), where "R" is any organic structure. Sulfur is present in oxidation state 0.

<span class="mw-page-title-main">Thorium compounds</span> Chemical compounds

Many compounds of thorium are known: this is because thorium and uranium are the most stable and accessible actinides and are the only actinides that can be studied safely and legally in bulk in a normal laboratory. As such, they have the best-known chemistry of the actinides, along with that of plutonium, as the self-heating and radiation from them is not enough to cause radiolysis of chemical bonds as it is for the other actinides. While the later actinides from americium onwards are predominantly trivalent and behave more similarly to the corresponding lanthanides, as one would expect from periodic trends, the early actinides up to plutonium have relativistically destabilised and hence delocalised 5f and 6d electrons that participate in chemistry in a similar way to the early transition metals of group 3 through 8: thus, all their valence electrons can participate in chemical reactions, although this is not common for neptunium and plutonium.

Pnictogen hydrides or hydrogen pnictides are binary compounds of hydrogen with pnictogen atoms covalently bonded to hydrogen.

Tellurium compounds are compounds containing the element tellurium (Te). Tellurium belongs to the chalcogen family of elements on the periodic table, which also includes oxygen, sulfur, selenium and polonium: Tellurium and selenium compounds are similar. Tellurium exhibits the oxidation states −2, +2, +4 and +6, with +4 being most common.

<span class="mw-page-title-main">Sulfoxylic acid</span> Chemical compound

Sulfoxylic acid (H2SO2) (also known as hyposulfurous acid or sulfur dihydroxide) is an unstable oxoacid of sulfur in an intermediate oxidation state between hydrogen sulfide and dithionous acid. It consists of two hydroxy groups attached to a sulfur atom. Sulfoxylic acid contains sulfur in an oxidation state of +2. Sulfur monoxide (SO) can be considered as a theoretical anhydride for sulfoxylic acid, but it is not actually known to react with water.

<span class="mw-page-title-main">Aluminium compounds</span>

Aluminium (British and IUPAC spellings) or aluminum (North American spelling) combines characteristics of pre- and post-transition metals. Since it has few available electrons for metallic bonding, like its heavier group 13 congeners, it has the characteristic physical properties of a post-transition metal, with longer-than-expected interatomic distances. Furthermore, as Al3+ is a small and highly charged cation, it is strongly polarizing and aluminium compounds tend towards covalency; this behaviour is similar to that of beryllium (Be2+), an example of a diagonal relationship. However, unlike all other post-transition metals, the underlying core under aluminium's valence shell is that of the preceding noble gas, whereas for gallium and indium it is that of the preceding noble gas plus a filled d-subshell, and for thallium and nihonium it is that of the preceding noble gas plus filled d- and f-subshells. Hence, aluminium does not suffer the effects of incomplete shielding of valence electrons by inner electrons from the nucleus that its heavier congeners do. Aluminium's electropositive behavior, high affinity for oxygen, and highly negative standard electrode potential are all more similar to those of scandium, yttrium, lanthanum, and actinium, which have ds2 configurations of three valence electrons outside a noble gas core: aluminium is the most electropositive metal in its group. Aluminium also bears minor similarities to the metalloid boron in the same group; AlX3 compounds are valence isoelectronic to BX3 compounds (they have the same valence electronic structure), and both behave as Lewis acids and readily form adducts. Additionally, one of the main motifs of boron chemistry is regular icosahedral structures, and aluminium forms an important part of many icosahedral quasicrystal alloys, including the Al–Zn–Mg class.


  1. "CIA – The world factbook". Central Intelligence Agency . Retrieved 18 August 2016.
  2. "About the International Decade for Action 'Water for Life' 2005-2015".
  3. 1 2 Greenwood and Earnshaw, pp. 766–7
  4. Sumathi, K.; Balasubramanian, K. (1990). "Electronic states and potential energy surfaces of H2Te, H2Po, and their positive ions". Journal of Chemical Physics. 92 (11): 6604–6619. Bibcode:1990JChPh..92.6604S. doi:10.1063/1.458298.
  5. Greenwood and Earnshaw, p. 623
  6. Greenwood and Earnshaw, p. 682
  7. Goldbach, Andreas; Saboungi, Marie-Louise; Johnson, J. A.; Cook, Andrew R.; Meisel, Dan (2000). "Oxidation of Aqueous Polyselenide Solutions. A Mechanistic Pulse Radiolysis Study". J. Phys. Chem. A. 104 (17): 4011–4016. Bibcode:2000JPCA..104.4011G. doi:10.1021/jp994361g.
  8. Hop, Cornelis E. C. A.; Medina, Marco A. (1994). "H2Te2 Is Stable in the Gas Phase". Journal of the American Chemical Society . 1994 (116): 3163–4. doi:10.1021/ja00086a072.
  9. Gerbaux, Pascal; Salpin, Jean-Yves; Bouchoux, Guy; Flammang, Robert (2000). "Thiosulfoxides (X2S=S) and disulfanes (XSSX): first observation of organic thiosulfoxides". International Journal of Mass Spectrometry. 195/196: 239–249. Bibcode:2000IJMSp.195..239G. doi:10.1016/S1387-3806(99)00227-4.
  10. Greenwood and Earnshaw, pp. 633–8
  11. 1 2 Dobado, J. A.; Martínez-García, Henar; Molina, José; Sundberg, Markku R. (1999). "Chemical Bonding in Hypervalent Molecules Revised. 2. Application of the Atoms in Molecules Theory to Y2XZ and Y2XZ2 (Y = H, F, CH3; X = O, S, Se; Z = O, S) Compounds". J. Am. Chem. Soc. 121 (13): 3156–3164. doi:10.1021/ja9828206.
  12. R. Steudel "Inorganic Polysulfanes H2S2 with n > 1" in Elemental Sulfur and Sulfur-Rich Compounds II (Topics in Current Chemistry) 2003, Volume 231, pp 99-125. doi : 10.1007/b13182
  13. 1 2 3 Greenwood and Earnshaw, p. 683
  14. Laitinen, Risto S.; Pakkanen, Tapani A.; Steudel, Ralf (1987). "Ab initio study of hypervalent sulfur hydrides as model intermediates in the interconversion reactions of compounds containing sulfur–sulfur bonds". J. Am. Chem. Soc. 109 (3): 710–714. doi:10.1021/ja00237a012.
  15. Nishimoto, Akiko; Zhang, Daisy Y. (2003). "Hypervalency in sulfur? Ab initio and DFT studies of the structures of thiosulfate and related sulfur oxyanions". Sulfur Letters. 26 (5/6): 171–180. doi:10.1080/02786110310001622767. S2CID   95470892.
  16. Liu, Yunxian; Duan, Defang; Tian, Fubo; Li, Da; Sha, Xiaojing; Zhao, Zhonglong; Zhang, Huadi; Wu, Gang; Yu, Hongyu; Liu, Bingbing; Cui, Tian (2015). "Phase diagram and superconductivity of polonium hydrides under high pressure". arXiv: 1503.08587 [cond-mat.supr-con].
  17. Cacace, F.; de Petris, G.; Pepi, F.; Troiani, A. (1999). "Experimental Detection of Hydrogen Trioxide". Science. 285 (5424): 81–82. doi:10.1126/science.285.5424.81. PMID   10390365.
  18. Wiberg 2001, p. 497
  19. Xiao, M. & Gaffney, T. R. Tellurium (Te) Precursors for Making Phase Change Memory Materials. (Google Patents, 2013) (https://www.google.ch/patents/US20130129603)