What is Electron Geometry?
“The electron geometry describes the spatial arrangement of a molecule’s bonds and lone pairs. VSEPR theory can be used to calculate electron geometry.”
The term electron geometry is the name of the electron pair/groups/domains on the central atom, whether they are bonding electrons or non-bonding electrons. Electron pairs are electrons that exist in pairs or bonds, as lone pairs or as a single unpaired electron. Because electrons are always in motion and their paths cannot be precisely defined, the electron arrangement in a molecule is described in terms of an electron density distribution.
Table of Contents
- How to Determine Electron Geometry?
- Calculation of Electron Geometry
- Difference between Electron Geometry and Molecular Geometry
- Frequently Asked Questions– FAQs
How to Determine Electron Geometry?
The electron group determines electron geometry:
- 2 electron groups, linear
- 3 electron groups, trigonal-planar
- 4 electron groups, tetrahedral
- 5 electron groups, trigonal-bipyramidal
- 6 electron groups, octahedral
Linear Electron Geometry
Linear geometry involves a central atom with two pairs of bonding electrons at a 180° angle (a straight line).
Trigonal Planar Electron Geometry
Trigonal planar electron geometry consists of a central atom with three pairs of bonding electrons arranged in a plane or “flat” at 120° angles to each other.
Tetrahedral Electron Geometry
Tetrahedral electron geometry consists of a central atom surrounded by four pairs of bonding electrons at 109.5° angles from each other, forming a tetrahedron-like shape.
Trigonal Bipyramidal Electron Geometry
A central atom with five pairs of bonding electron pairs is known as trigonal bipyramidal.
It has the shape of three pairs in a plane at 120° angles (the trigonal planar geometry) and the remaining two pairs at 90° angles to the plane. The shape is similar to two pyramids joined by a triangular base.
Octahedral Electron Geometry
The central atom in octahedral electron geometry has six pairs of bonding electrons that are all at 90° to one another. The shape is similar to two pyramids joined together by a square base.
Calculation of Electron Geometry
The steps to be followed in making the determination are as follows.
- Predict the molecule’s central atom. It should be the atom with the highest electronegative potential.
- The number of valence electrons in the central atom must be determined.
- Calculate the total number of electrons donated by other atoms.
- Determine the total number of electrons surrounding the central atom.
- Subtract that number from two. This number represents the number of electron groups present.
- Subtract the steric number from the number of single bonds present around the central atom.
- This number represents the number of lone electron pairs in the molecule.
- Determine the geometry of the electron.
Example:
Electron Geometry of CH4
The molecule’s central atom is denoted by the letter C.
The number of valence electrons in C is equal to four.
The number of electrons donated by hydrogen atoms is equal to 4 x (H) = 4 x 1 = 4.
Total number of electrons in the vicinity of C = 4 + 4 = 8
The number of electron groups is eight which is divided by two, which equals four.
The number of single bonds present is equal to four.
Count of lone electron pairs = 4 – 4 = 0
As a result, electron geometry = tetrahedral.
Difference between Electron Geometry and Molecular Geometry
The name of the geometry of the electron pair/groups/domains on the central atom, whether they are bonding electrons or non-bonding electrons, is referred to as electron geometry. It enables us to understand how different electron groups in a molecule are arranged. Molecular geometry, on the other hand, is the three-dimensional structure of atoms in a molecule that determines its shape. It aids in comprehending the entire atom and its arrangement.
If all of the electron groups are bonded, and there are no lone pairs, the electron geometry and molecular geometry are the same.
Read more: Molecular geometry
Frequently Asked Questions on Electron Geometry
Are electron geometry and molecular geometry the same?
Molecular geometry and electronic geometry have different definitions. They are distinguished by the fact that molecular geometry refers to the arrangement of atoms in a molecule around the central atom(s), whereas electron geometry refers to the arrangement of electron density around the central atom(s).
How to determine electron geometry?
The number of electron pairs, both bonding and non-bonding pairs, around the central atom can be used to calculate electron geometry.
How does the electron geometry change if you replace a bond with a lone pair?
The arrangement of electron groups is referred to as electron geometry. If lone pairs of electrons, or electrons that are not bonded to other atoms, are found in the molecule, the molecular geometry, not the electron geometry, will change.
Demonstrate H2O electron geometry vs molecular geometry.
The central oxygen atom has six valence electrons, two of which form two bond pairs with the hydrogen atoms and the remaining four electrons form two lone pairs. This produces a tetrahedral electron geometry rather than a bent molecular geometry.
Define molecular geometry.
The arrangement of atoms in a molecule, usually relative to a single central atom, is known as molecular geometry.
It excludes lone pairs from determining a molecule’s shape, though repulsion from lone pair(s) is taken into account only in bond angles.
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