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 (H2OH2O), 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):
- Identify the Central Atom: Nitrogen
- Count the Bonded Atoms: 3 hydrogens
- Identify Lone Pairs on Nitrogen: 1 pair
- 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.
Most Common FAQs
It is a numeric value used to predict the shape of a molecule based on the regions of electron density around a central atom.
Simply add the number of atoms bonded to the central atom to the number of lone pairs on the central atom.
It determines the molecular geometry, which is critical for understanding the physical and chemical properties of the molecule.
