SO properties (25 Facts You Should Know)

SO or sulfur monoxide is the oxide of sulfur which is non-metal oxide and belongs to group 16 elements. Let us discuss SO in this article.

SO consists of O and S elements; like them, it also has a triplet ground state term.  Near the IR region, the molecule gets excited and changes to the singlet. In the singlet state, no unpaired electrons are present, and consider it more reactive. it can be prepared by the reaction of SO2 and O3.

It can also be synthesized by the decomposition of ethylene episulfoxide in the laboratory. Now in the following part of the article, we have to know about the basic property of So related to its physical as well as chemical nature like, melting and boiling point, reaction nature, molar mass, viscosity, etc.

1. SO IUPAC name

The IUPAC name of SO is thionyl monoxide, because in the IUPAC naming system S is called thio, and 1 is mono. So here one oxygen atom is attached to sulfur and formed an oxide, so it is called thionyl monoxide because the number of oxygen lies before the attached oxygen atom. It is also called sulfinyl.

2. SO chemical formula

The chemical formula of SO is S1O1 because the molecule consists of only one sulfur and one oxygen atom. There are no other atoms present and both have only one component so the suffix used is 1 but in convention, we cannot use 1 as a suffix so the actual chemical formula is SO which represents the number of elements.

SO Chemical Formula

3. SO CAS number

13827-32-2 is the CAS number of SO which is given by the chemical abstract service and with the help of this number we can get to know the physical property of the molecule.

4. SO Chem Spider ID

102805 is the Chem spider ID for SO which is given by the royal society of chemistry.

5. SO chemical classification

SO is classified into the following categories,

  • SO is a non-metal oxide
  • SO is an acidic oxide
  • SO is a gaseous molecule with neutral nature
  • So is an inorganic covalent molecule

6.  SO molar mass

The molar mass of the SO is 48.064 g/mol. Because the mass of the SO is calculated in grams for one mol of the compound. It is the sum of the atomic mass of S and O. The atomic mass of S is 32.064 g/mol and of O is 15.999 g/mol. So, the molar mass of SO is 32.064 + 15.999 = 48.064 g/mol.

7.  SO color

SO has no particular color, it is colorless. Because the energy of the electronic transition between S and O is very high so the corresponding wavelength for this transition is very low and appears no color in the visible region, but when it is condensed the energy will be decreased and the color appears orange-red.

8. SO viscosity

The viscosity of SO is 0.0124mPa at 180C temperature. Viscosity is one kind of frictional force for liquid but SO exists in gaseous so its value is very low. It can be calculated by the formula, F = µA(u/y), where F is the applied force, µ is the viscosity, A is the area, and (u/y) is the rate of deformation.

9. SO molar density

The molar density of the SO is 1.434 g/L because it has a molar mass of 48.064 g/mol and the volume of the SO as per Avagarod’s calculation is 2*22.4 L = 44.8 L, so the density will be 48.064/44.8 = 1.434 g/L. although it has vapor density as it exists in gaseous form and the value is 2.26 g/mL.

10. SO melting point

The melting temperature for SO is -750C or 198K, because SO exists as gaseous at room temperature, so it required very low energy to exist in its solid and liquid form and for this reason, the melting temperature is very low even more negative.

11. SO boiling point

The boiling point of SO is -120C or 261K because it can exist gaseous at room temperature so its liquid state exists at negative temperature and even at very low temperatures it can be boiled off. The van der Waal’s attraction force is very low so less energy is to be required.

12. SO state at room temperature

SO exists in gaseous form at room temperature, because the van der waal’s force of attraction is very low for this molecule and also the standard molar enthalpy is highly positive so it can stay the molecule in gaseous form at room temperature.

13. SO covalent bond

SO has a covalent bond, and the electrons in the bond share properly with S as well as O. the central S is sp2 hybridized and hybridization only occurs for the covalent bond not for an ionic bond, because in the hybridization two or more atoms shares their electrons to make a proper bond in between them.

14. SO covalent radius

SO has a radius of 166 pm which is its van der waal’s radius because the covalent radius is applicable for homonuclear molecules but SO is a heteronuclear molecule so we just add the radius of O and S and divided by two as two atoms are present to get the van der waal’s radius to consider both atoms are a sphere.

15. SO electron configurations

Electron configuration is the arrangement of electrons in a particular shell having a particular quantum number of an element. Let us find the electron configuration of SO.

SO has two bond pairs and four lone pairs of electrons, as it is a molecule and we cannot find the electronic configuration for a molecule like an atom. Here both S and O contain two lone pairs each and due to the double bond two bond pairs are present, each pair consists of two electrons.

16. SO oxidation state

The oxidation state of SO is 2, because here we predict the oxidation state of either S or O and both have the same oxidation state. As there are two bonds present between O and S so two electrons are missing from their valence orbital and that should be considered as their oxidation state.

17. SO acidity/alkaline

SO is an acidic oxide, because when it reacts with water it forms acids and we know that all the non-metal oxides are acidic in nature and meta oxides are basic.

18. Is SO odorless?

SO is an odorless gaseous molecule, so it does not have any characteristic odor in it.

19. Is SO paramagnetic?

The paramagnetic nature of a molecule depends on the availability of unpaired electrons in the valence shell. Let us see whether SO is paramagnetic or not.

In the triplet state SO is paramagnetic in nature because in that particular form it has unpaired electrons, but when the molecule gets excited it transforms to a singlet state, and there are no unpaired electrons present and then the molecule will be diamagnetic in nature.

20. SO hydrates

SO has no hydrate part because in the crystal form there are no water molecules present in it hydrates come in the crystal of metallic compounds and neither S nor O are metal.

21. SO crystal structure

SO has an orthorhombic crystal in the solid form and it is stable at very low temperatures like -750C.

22. SO polarity and conductivity

SO is non-conductive because there is no electrolytic nature present but it is a polar molecule because there is a dipole-moment present between molecules.

23. SO reaction with acid

SO reacts only with super acid because it is acidic oxide and the basic property present is very low. It first converts to sulfur dioxide and then reacts with acid.

C6(CH3)6 + SO2 + 3 HF·AsF5 → [C6(CH3)6SO][AsF6]2 + [H3O][AsF6]

24. SO reaction with base

Being an acidic oxide it can react with the main strong base after converting to sulfur dioxide because there is an equilibrium present between sulfur monoxide and sulfur dioxide.

SO2 + 2NaOH → Na2SO3 + H2O.

25. SO reaction with oxide

SO reacts with oxygen to form sulfur dioxide and sulfur dioxide further reacts with oxygen to form sulfur trioxide.

  • SO + O = SO2
  • SO2 + O = SO3

26. SO reaction with the metal

SO not reacts with metal rather SO2 reacts with the metal to form metallic oxide and separation of sulfur and if the reaction presence of water then hydrogen sulfide will be formed.

  • SO2 + M (transition metal) = MO + S +O2
  • SO2 + M + H2O = MO + H2S + O2


SO is non-metal oxide and it is found in the atmosphere it caused air pollution because it forms sulfur di-oxide which is not good for human beings. The singlet SO can react with different organic molecules and can serve as a radical initiator.

Read more about Lawrencium Properties.

Read more following properties

Aluminium hydrides
Aluminium Chemical Properties
Magnesium hydride(MgH2)
Phosphorus Triiodide(PI3)
Boron Chemical
Nitrogen Dioxide(NO2)
Phosphorus Trichloride(PCl3)
Sulfur Trioxide(SO3)
Carbon Tetrafluoride (CF4)
Propanoic Acid (CH3CH2COOH)
Barium Hydroxide(Ba(OH)2)
Silicon Chemical Properties

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