Molecular Geometry vs Electron-Pair Geometry

(Polar molecules, Non-polar molecules, etc.)

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Stevin1H
Posts: 89
Joined: Fri Sep 28, 2018 12:17 am

Molecular Geometry vs Electron-Pair Geometry

Postby Stevin1H » Thu Nov 15, 2018 1:13 am

Can someone please explain the difference in molecular geometry vs electron-pair geometry? What defines the molecular geometry and what defines the electron-pair geometry?

Jim Brown 14B Lec1
Posts: 62
Joined: Fri Sep 28, 2018 12:28 am

Re: Molecular Geometry vs Electron-Pair Geometry

Postby Jim Brown 14B Lec1 » Thu Nov 15, 2018 6:42 am

Molecular geometry takes into account only the atoms surrounding the central atom. This includes shapes like bent, trigonal pyramidal, square planar, etc. Electron-pair geometry is based on the number of electron density fields. This includes only the basic geometries (linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral).

Mindy Kim 4C
Posts: 65
Joined: Fri Sep 28, 2018 12:25 am

Re: Molecular Geometry vs Electron-Pair Geometry

Postby Mindy Kim 4C » Thu Nov 15, 2018 10:53 am

An example of this is a molecule with three atoms and two bonding pairs and one lone electron pair. The electron geometry for this molecule would be trigonal planar because there are 3 different electron densities. However, the molecular shape for this molecule would be bent because only the atoms are considered in the shape.

Katie_Duong_1D
Posts: 69
Joined: Fri Sep 28, 2018 12:27 am

Re: Molecular Geometry vs Electron-Pair Geometry

Postby Katie_Duong_1D » Fri Nov 16, 2018 11:07 am

Molecular geometry does not consider lone pairs as areas of electron density. An example would be a molecule with VSEPR formula AX4E2. There are 6 bonding regions, 4 bonding pairs and 2 lone pairs. AX4E2 is square planar (molecular geometry). The electron geometry of this molecule would be octahedral because there are 6 bonding regions all. The lone pairs and bonding pairs are both considered in electron pair geometry.

David S
Posts: 54
Joined: Fri Sep 28, 2018 12:15 am

Re: Molecular Geometry vs Electron-Pair Geometry

Postby David S » Fri Nov 16, 2018 11:45 am

Electron pair geometry accounts for lone pairs and bonding pairs. Since it discounts the differences in strength of repulsion between the different types of electron density regions, the electron pair geometry gives us the idealized (equal repulsion) bond angles around a designated central atom; bonding pairs and lone pairs are depicted as if they are the same, and the atoms surrounding the central atom are discrarded. Thus, electron geometries serve as a good reference for predicting the actual bond angles in a molecule.

Molecular geometry displays all constituent atoms in the molecule and all electron density regions; lone pairs are depicted differently from bonding regions. The main difference is that molecular geometry accounts for the additional strength of repulsion that lone pairs have on bonding pairs, resulting in the classification and consideration of new geometry types with bond angles that differ slightly (often less than) the ideal bond angles of their respective electron pair geometries.


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