All about VSEP Number

The VSEP is generally used to define a molecule’s shape.

The total number of electrons in the outermost shell of the core atom must be counted.It is necessary to count the total number of electrons from other atoms that are used in bonding with the central atom. Combine these two quantities to yield the valence shell electron pair number, or VSEP number.

How To Find Your VSEP Number

You must first locate the central atom.

Then you must count the number of valence electrons in the centre atom.

For each bonding atom, the third step is to perform a simple addition of one electron.

Following that, you must add or delete electrons based on their charge. This means that for negative ions, the valence electrons must be multiplied by the number of electrons equivalent to the negative charge units on the ions.

For positive ions, remove the number of valence electrons equal to the units of positive charge on the ion from the total number of electrons.

Finally, divide the sum you’ve arrived at by two. This will assist you in determining the overall number of electron pairs in the system.

Your VSEPR number is the answer you get.

VSEP                      Number Shape of the Molecule

2                              Linear

3                              Trigonal Planar

4                             Tetrahedral

5                             Trigonal Bipyramidal

6                             Octahedral

7                            Pentagonal Bipyramidal

Linear Molecular Geometry

The linear molecular geometry depicts the geometry surrounding a central atom that is connected to two additional atoms at an angle of 180 degrees. The carbon centres of linear organic compounds like acetylene (HCCH) are frequently explained using sp orbital hybridization.

Linear geometry occurs at centre atoms with two bound atoms and zero or three lone pairs (AX₂ or AX₂E₃) in the AXE notation, according to the VSEPR model. Neutral AX₂ molecules with linear geometry include beryllium fluoride (FBeF) with two single bonds, carbon dioxide (O=C=O) with two double bonds, and hydrogen cyanide (HCN) with one single and one triple bond.Acetylene is the most important linear molecule with more than three atoms, with each of its carbon atoms acting as a core atom with a single hydrogen bond and a triple connection to the other carbon atom.

Trigonal Planar

A molecular geometry model with one atom in the centre and three atoms at the corners of an equilateral triangle, known as peripheral atoms, all on one plane is known as trigonal planar.

In an ideal trigonal planar species, all three ligands are identical, and all bond angles are 120°. Molecules like H₂CO depart from this idealised geometry because the three ligands are not equivalent. Boron trifluoride (BF₃), formaldehyde (H₂CO), phosgene (COCl₂), and sulphur trioxide are examples of compounds with trigonal planar geometry (SO₃).

Tetrahedral Molecular Geometry

A central atom is located at the centre of a tetrahedral molecular geometry, with four substituents located at the tetrahedron’s corners.When all four substituents are the same, as in methane (CH₄) and its heavier counterparts, the bond angles are 109.5°. Point group Td includes methane and other totally symmetrical tetrahedral molecules, although most tetrahedral molecules have lesser symmetry. Chiral tetrahedral molecules are possible

The majority of Si, Ge, and Sn compounds are tetrahedral, with the exception of practically all saturated organic compounds. As in xenon tetroxide (XeO4), the perchlorate ion (ClO₄), the sulphate ion (SO₂^4-), and the phosphate ion (PO₃⁴), tetrahedral molecules frequently have multiple bonding to the outer ligands. The sulfur-to-nitrogen triple bond is present in thiazyl trifluoride (SNF₃), which is tetrahedral.

A Trigonal Bipyramid

In chemistry, a trigonal bipyramid formation is a molecular shape with one atom in the centre and five other atoms in the corners of a triangular bipyramid.Because there is no geometrical configuration with five terminal atoms in equivalent places, the bond angles surrounding the central atom are not identical (see also pentagonal bipyramid). This molecular geometry can be found in the gas phase in the forms of phosphorus pentafluoride (PF₅) and phosphorus pentachloride (PCl₅).

Octahedral Molecular Geometry

Octahedral molecular geometry describes the structure of compounds with six atoms or groups of atoms or ligands symmetrically clustered around a central atom, which define the vertices of an octahedron.Sulfur hexafluoride SF₆ and molybdenum hexacarbonyl Mo(CO)₆ are examples of octahedral chemicals.

Pentagonal Bipyramid

A pentagonal bipyramid is a molecular shape in chemistry that has one atom in the centre and seven ligands at the corners. The pentagonal bipyramid is a situation in which the bond angles surrounding an atom aren’t all the same. Iodine heptafluoride (IF7) with 7 bonding groups is an example of this.

Theory of VSEPR

The Valence Shell Electron Pair Repulsion Theory, or VSEPR theory, is based on the idea that all atoms have a repulsion between their pairs of valence electrons, and that the atoms will always want to arrange themselves in a way that minimises this repulsion

Conclusion

As a result, according to VSEPR theory, repulsion by a lone pair is stronger than repulsion by a bonded pair. As a result, when a molecule has two interactions with differing degrees of repulsion, VSEPR theory predicts that lone pairs will occupy places that reduce repulsion.