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:
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

The geometry of [AsPh4]+. You can use your mouse to manipulate the molecule in the right hand "Jmol" image.