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VSEPR calculation for the tetaraphenylarsonium cation, [AsPh4]+

There are four σ-bonded phenyl groups attached to arsenic in the tetraphenylarsonium cation and the calculation predicts no lone pairs on the central atom. The tetraphenylarsonium cation is also useful in synthesis, this time for its ability to aid the crystallization of bulky anions by providing a good size match. Note that the positive charge is placed formally on arsenic, even though it is in reality delocalized over the whole molecule.

Tetraphenylarsonium, [AsPh4]+
Lewis structure: AsPh4cation.gif
Central atom arsenic
Valence electrons on central atom: 5
4 Ph groups each contribute 1 electron: 4
Subtract one for the positive charge on As -1
Total: 8
Divide by 2 to give electron pairs 4
4 electron pairs: tetrahedral geometry for the four shape-determining electron pairs
AsPh4cation
The geometry of [AsPh4]+. You can use your mouse to manipulate the molecule in the right hand "Jmol" image.

A VSEPR tutorial on the WWW

VSEPR tutorial on the WWW, URL: http://winter.group.shef.ac.uk/vsepr/
Copyright 1996-2015 Prof Mark Winter [The University of Sheffield]. All rights reserved.
Document served: Friday 24th March, 2017