Question

How do you determine steric numbers?

Answer 1

Hint: As we know that steric number is the number of atoms that are bonded to a central atom of a molecule plus the number of lone pairs that are attached to the central atom.

Complete step by step answer:
- As we know that steric number of a molecule is used to determine the molecular geometry in the valence shell electron pair repulsion theory.
- It is found that steric numbers can help to determine the hybridization of an atom in a molecule.
- We can calculate the value of steric number by summing up the total number of atoms that are bonded to the central atom and the lone pairs of electrons that are present on the central metal atom.
- It is found that if the value of steric number is 2 then the hybridization of the molecule is sp
- It is found that if the value of steric number is 3 then the hybridization of the molecule is $s{{p}^{2}}$
- It is found that if the value of steric number is 4 then the hybridization of the molecule is $s{{p}^{3}}$
- Let us take an example of sulphuric acid. We can calculate the steric number of sulphuric acid as:
- Steric number = No. of atoms that are bonded to the central atom + No. of lone pairs in the central atom.
- We can see the structure of sulphuric acid as:

- No. of atoms that are bonded to central atom=4, No. of lone pairs in sulphur=0, so substituting the value we get:
Steric number= 4 + 0 = 4.
- Hence, in this way we can calculate the steric number.

Note: - As we know that by knowing the value of steric number we can determine the hybridization of the molecule. And it is also found that we can also find the shape of the molecule by knowing the value of steric number.
- It is found that if the value of steric number is 2 then the shape is linear, when steric number is 3 then the shape is trigonal planar and if the steric number is 4 then the shape is tetrahedral.