Disulfur is the
diatomic molecule
Diatomic molecules () are molecules composed of only two atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen () or oxygen (), then it is said to be homonuclear. O ...
with the formula S
2. It is analogous to the
dioxygen
There are several known allotropes of oxygen. The most familiar is molecular oxygen (O2), present at significant levels in Earth's atmosphere and also known as dioxygen or triplet oxygen. Another is the highly reactive ozone (O3). Others are:
* ...
molecule but rarely occurs at room temperature. This violet gas is the dominant species in hot sulfur vapors. S
2 is one of the minor components of the atmosphere of
Io, which is predominantly composed of
SO2. The instability of S
2 is usually described in the context of the
double bond rule
In chemistry, the double bond rule states that elements with a principal quantum number greater than 2 for their valence electrons ( period 3 elements and higher) tend not to form multiple bonds (e.g. double bonds and triple bonds). The double b ...
.
Synthesis
This violet gas is generated by heating sulfur above 720 °C, comprising 99% of the vapor at low pressure (1 mm Hg) at 530 °C.
Disulfur can be produced when an atmosphere of
COS is irradiated with UV light using a mercury
photosensitizer
Photosensitizers produce a physicochemical change in a neighboring molecule by either donating an electron to the substrate or by abstracting a hydrogen atom from the substrate. At the end of this process, the photosensitizer eventually returns t ...
or when CS
2, H
2S
2, S
2Cl
2 or C
2H
4S, PSF
3 or COS are irradiated.
Natural occurrence
Gaseous disulfur has been detected emanating from the surface of Jupiter's moon
Io, from the vicinity of
Pele volcano.
Properties
The ground state of S
2 is a
triplet: a
diradical
In chemistry, a diradical is a molecular species with two electrons occupying molecular orbitals (MOs) which are degenerate. The term "diradical" is mainly used to describe organic compounds, where most diradicals are extremely reactive and i ...
, with two unpaired electrons like O
2 and
SO. It has the S-S bond length of 189 pm, much shorter than the S-S single bonds in S
8, which are 206 pm long. Its
Raman spectrum
Raman spectroscopy () (named after Indian physicist C. V. Raman) is a Spectroscopy, spectroscopic technique typically used to determine vibrational modes of Molecule, molecules, although rotational and other low-frequency modes of systems may als ...
consists of a band at 715 cm
−1. The corresponding O-O band for O
2 is found at 1556 cm
−1. The S-S
bond energy
In chemistry, bond energy (''BE''), also called the mean bond enthalpy or average bond enthalpy is the measure of bond strength in a chemical bond. IUPAC defines bond energy as the average value of the gas-phase bond-dissociation energy (usually ...
is 430 kJ/mol compared to 498 kJ/mol for O
2.
[(]
Disulfur readily
photodissociates,
with a mean lifespan of 7.5 min in sunlight.
References
External links
*
{{diatomicelements
Allotropes of sulfur
Homonuclear diatomic molecules
Gases with color