Electronic Geometry
Definition and meaning of Electronic Geometry in chemistry.
Electronic geometry is the three-dimensional arrangement of all electron domains, bonding pairs and lone pairs, around a central atom that minimizes electron-electron repulsion, as described by VSEPR (valence shell electron pair repulsion) theory.
In more detail
Because electron domains repel each other, they spread out to the positions of greatest mutual distance, giving predictable shapes such as linear, trigonal planar, tetrahedral, trigonal bipyramidal, or octahedral depending on the total number of domains (2 through 6). Electronic geometry counts lone pairs along with bonding pairs, whereas molecular geometry describes only the positions of the bonded atoms, so the two names can differ for molecules with lone pairs on the central atom. Lone pairs occupy more space than bonding pairs, which slightly compresses bond angles between bonding pairs.
Key facts
| Field | General Chemistry |
|---|---|
| Theory used | VSEPR (valence shell electron pair repulsion) |
| Determined by | Total number of electron domains (bonding + lone pairs) |
| Common shapes | Linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral |
In ammonia, NH3, nitrogen has three bonding pairs and one lone pair (four electron domains), so the electronic geometry is tetrahedral, while the molecular geometry (describing only the three N-H bonds) is trigonal pyramidal.
Frequently asked questions
Is electronic geometry the same as molecular geometry?
No. Electronic geometry includes lone pairs in the count of electron domains, while molecular geometry describes only the positions of the atoms bonded to the central atom. They are identical only when the central atom has no lone pairs.
Why do lone pairs affect bond angles even though they aren't 'seen' in molecular geometry?
Lone pairs occupy more space around the central atom than bonding pairs because they are held only by one nucleus, so they push bonding pairs closer together, slightly reducing bond angles from the ideal electronic-geometry values.