SO3 Molecular Geometry and Bond Angles

Lewis Structure of SO3 (Sulfur Trioxide)
Lewis Structure of SO3 (Sulfur Trioxide)

The chemical substance sulphur trioxide (also known as nisso sulfan) has the formula SO3 (alternative spelling: sulphur trioxide). “Unquestionably the most significant commercially”, according to Sulphur Oxide. It is produced in enormous quantities as a precursor to sulphuric acid. Sulphur trioxide comes in various forms, including gaseous monomers, crystalline trimers, and solid polymers. Sulphur trioxide is solid with a narrow liquid range at slightly below ambient temperature. Acid rain is mostly caused by gaseous SO3. A Lewis Structure is a depiction of a molecule’s valence shell electrons. It’s used to depict how electrons in a molecule are distributed. The most interesting topic is the molecular geometry of sulphur trioxide.

Molecular Geometry of Sulphur Trioxide

The three-dimensional structure of the atoms that aids in forming a molecule is known as molecular geometry. It can tell you about reactivity, polarity, colour, attraction, and biological activity, among other things.

In Sulphur Trioxide, one sulphur atom and three oxygen atoms are stretched as far apart as possible! Electrons encircle oxygen atoms. Negative electrons repel negative electrons.

AXN is another way to remember the molecular geometry of SO3.

  • Sulphur, the centre atom, is represented by the letter A.
  • The letter X denotes the number of atoms bound to central sulphur.
  • Any nonbonding electron pairs are denoted by the letter N.
  • Because there are no nonbonding electrons in this SO3 formula, we don’t need to worry about N. Furthermore, because there are three oxygen atoms, the result will be X3.

As a result, the SO3 molecule has AX3. (By the way, this is why SO3 has a Trigonal Planar form.) SO3 has a bond angle of 120 degrees.

SO3 Molecular geometry – Lewis structure

  • Count how many Valence Electrons each atom contributes to the equation. SO3 has a total of 24 electrons. SO3 2- has a total of 26 electrons.
  • Place the atom with the least electronegative charge in the middle. Sulphur is present in both situations.
  • There are three of them when you put the more electronegative atoms surrounding the Sulphur atom.
  • Draw six valence electrons in pairs of two around each atom (since they all have six).
  • There are a total of 12 electrons between the one Sulphur atom and the three Oxygen atoms.
  • Make double bonds. A single bond requires two electrons to form. A double bond requires four electrons to form.
  • There is no tax on sulphur trioxide. Because Sulphur is weak compared to Oxygen, it surrenders its electrons to the oxygen atoms because they are so electronegative.

SO3 molecular geometry – What causes SO3 to generate double bonds?

The chemical sulphur trioxide has a trigonal planar structure. Sulphur occupies the molecule’s centre because it is less electronegative than Oxygen. It possesses six electrons and shares them all with the three Oxygen atoms, forming double bonds.

How does Sulphur break the octet rule?

In SO3 molecular geometry, Sulphur has a valence electron count of six. In the 3s orbital, 2 is present, whereas, in the 3p orbital, 4 is present. To generate 8 valence electrons, it simply requires 2 additional electrons in the 3p orbital. Normally, this would imply that the anticipated formula for sulphur fluoride is SF2, not SF4. On the other hand, sulphur’s 3rd energy level electrons have access to the 3d sublevel. This means that more than 8 electrons can be supported as valence electrons.

The resulting orbital is called “dsp3 hybridised” since it is a hybrid. Around the sulphur, there is one lone pair and four bonding pairs of valence electrons. The d sublevel is not accessible to elements in the first two periods of the periodic table. They follow the octet rule as a result.

The hybridisation of SO3

SO3 has a sp2 hybridisation. It is calculated using the following formula:

Number of sigma bonds + Number of lone pairs = Number of hybrid orbitals

One sigma bond and one pi bond exist in a single shared double covalent bond.

So, in a single SO3 molecule, there are three sigma bonds and zero lone pairs (confirmed with the Lewis structure).

As a result, the number of hybrid orbitals is 3 + 0 = 3. One orbital and two p orbitals of the same shell within an atom overlap and mix to form three new hybrid orbitals of comparable energy in sp2 hybridisation.


Period 3 of the periodic table is characterised by elements that tend to extend their octet and accommodate more than eight valence electrons. It’s noteworthy to note that this behaviour is not unusual, as most elements, with the exception of period two elements, exhibit it. Because one sigma bond and one pi bond are formed in SO3, the hybridisation is sp2. This was all the information about SO3 molecular structure and SO3 molecular structure and bond angle examples. Hence, it is clear that SO3 is a nonpolar molecule that forms a bond of 120 degrees.

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