Tetrahedral arrangement of 4 electron pairs

The 20-electron group. This small group includes a number of ions and molecules formed by elements of Groups V, VI, and VII  

26-electron group. Pyramidal AO3 complexes include the SO3, SeO, Br03, and lOJ ions and the Xe03 molecule note the absence of the 

NF4 and NOF3 are known, but the highest oxyfluoride is NO2F, though NS3F has been prepared  

Note the complete vertical column of P complexes and the complete diagonal series of neutral molecules, from 81X4 to Xe04. 

Particular interest attaches to the 22, 28, and 34 electron systems because of the non-equivalence of the axial and equatorial positions in trigonal bipyramidal coordination, there being no spatial arrangement of five equivalent bonds around an atom other than the coplanar (pentagonal) one. 

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