What Is The Difference Between Electronic Geometry & Molecular Shape?
Electron geometry and molecular geometry are the arrangement of electrons or atoms around a central atom in three-dimensional space. This gives a molecule a particular shape and certain bond angles.
Are Electron Geometry and Molecular Geometry Definitions the Same?
The molecular geometry definition in chemistry is the arrangement of atoms in relation to a central atom in three-dimensional space.
Electron geometry is the arrangement of electron groups. If lone pairs of electrons, electrons not bonded to other atoms, are located in the molecule, this will change the molecular geometry, not the electron geometry.
If all the electron groups are bonded, with no lone pairs, then the electron geometry and molecular geometry are the same.
VSEPR and Geometry
Valance-shell electron repulsion (VSEPR) is a theory that proposes the geometry of a molecule based on minimizing the repulsion between electron pairs. This model is useful for most compounds with a central atom.
Electrons, whether bonded or in lone pairs, will repel each other, and they arrange around a central atom in a way that minimizes this repulsion and maximizes the distance between them.
Lone pairs of electrons will repel stronger than bonded ones, and this will alter the bond angles in the molecular geometry, making the angles slightly smaller.
Electron Geometry
Electron geometry is determined by electron group:
• 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 and Molecular Geometry
Linear geometry involves a central atom with two pairs of bonding electrons at an angle of 180 degrees (a straight line). This is the only possible shape for a linear geometry; the electron geometry and molecular geometry are the same.
Trigonal Planar Electron Geometry
Trigonal planar electron geometry is a central atom with three pairs of bonding electrons at 120-degree angles to each other arranged in a plane or "flat."
Only the trigonal planar has the same electron geometry and molecular geometry:
• trigonal planar: all three pairs of bonding electrons are bonded to atoms
• bent: two atoms bonded, one lone pair of electrons (Here, molecular geometry differs from
electron geometry, and, as stated above, the bond angle is slightly less than 120 degrees.)
Tetrahedral Electron Geometry
Tetrahedral electron geometry is a central atom surrounded by four pairs of bonding electrons at angles of 109.5 degrees from each other, forming a shape that resembles a tetrahedron.
Only the tetrahedral shape has the same electron geometry and molecular geometry:
• tetrahedral: all four pairs of bonding
electrons are bonded to atoms
• trigonal pyramidal: three atoms bonded, one
lone pair of electrons
• bent: two atoms bonded, two lone pairs of
electrons
Trigonal Bipyramidal Electron Geometry
Trigonal bipyramidal is a central atom with five pairs of bonding electron pairs.
The geometrical name comes from the shape of three pairs in a plane at 120-degree angles (the trigonal planar geometry) and the remaining two pairs at 90-degree angles to the plane. The shape resembles two pyramids with a triangular base attached together.
It is important to note that the lone electron pairs will fill the trigonal planar portion of the geometry first. Only the trigonal bipyramidal shape has the same electron geometry and molecular geometry:
• trigonal bipyramidal: all five pairs of bonding
electrons are bonded to atoms
• seesaw: four atoms bonded, one lone pair of
electrons
• t-shaped: three atoms bonded, two lone pairs of
electrons
• linear: two atoms bonded (located opposite to
each other), three lone pairs of electrons
Octahedral Electron Geometry
Octahedral electron geometry is a central atom with six pairs of bonding electrons, all of which are at 90 degrees to one another. The shape resembles two pyramids with a square base attached together.
Only the octahedral shape has both the electron geometry and molecular geometry the same. Note that there are no other combinations within this geometrical shape than those listed below:
• octahedral: all six pairs of bonding
electrons are bonded to atoms
• square pyramidal: five atoms bonded, one lone
pair of electrons
• square planar: four atoms bonded, two lone
pairs of electrons
Cite This Article
MLA
Kozlowski, Rosann. "What Is The Difference Between Electronic Geometry & Molecular Shape?" sciencing.com, https://www.sciencing.com/difference-electronic-geometry-molecular-shape-8750051/. 16 February 2020.
APA
Kozlowski, Rosann. (2020, February 16). What Is The Difference Between Electronic Geometry & Molecular Shape?. sciencing.com. Retrieved from https://www.sciencing.com/difference-electronic-geometry-molecular-shape-8750051/
Chicago
Kozlowski, Rosann. What Is The Difference Between Electronic Geometry & Molecular Shape? last modified August 30, 2022. https://www.sciencing.com/difference-electronic-geometry-molecular-shape-8750051/