Steric Number Calculator Online

The Steric Number (SN) is essential for determining the shape of a molecule based on the Valence Shell Electron Pair Repulsion (VSEPR) theory. The formula to calculate the steric number is straightforward:

SN = number of bonded atoms to the central atom + number of lone pairs on the central atom

This calculation helps in predicting the molecular geometry by considering the repulsion between electron pairs located around a central atom.

The Formula Explained of Steric Number Calculator

To use the steric number calculator, one needs to understand the components of the formula:

• Bonded Atoms: These are the atoms directly connected to the central atom.
• Lone Pairs: These are the pairs of electrons that do not participate in bonding but significantly influence the molecule’s shape.

For example, in a water molecule (H2OH2​O), oxygen is the central atom with two bonded hydrogens and two lone pairs, making the steric number 4, which corresponds to a tetrahedral geometry as per VSEPR theory.

Steric Numbers and Molecular Geometry: A Reference Table

The following table provides a quick reference to determine the molecular geometry from the steric number:

Steric Number	Molecular Geometry
2	Linear
3	Trigonal Planar
4	Tetrahedral
5	Trigonal Bipyramidal
6	Octahedral

This table serves as a handy guide for students and professionals when analyzing molecular structures.

Step-by-Step Example of Steric Number Calculator

Let’s calculate the steric number for ammonia (NH3NH3​):

1. Identify the Central Atom: Nitrogen
2. Count the Bonded Atoms: 3 hydrogens
3. Identify Lone Pairs on Nitrogen: 1 pair
4. Apply the Formula: SN = 3 (H atoms) + 1(lone pair) = 4

The steric number 4 indicates a tetrahedral geometry, which in the case of ammonia is slightly distorte to a trigonal pyramidal shape due to the lone pair.

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