Why Does IF5 Exhibit a Square Pyramidal Shape Despite Exceeding the Octet Rule?

[jolly_math]

Homework Statement

Predict the molecular structure of IF5 and its overall polarity.

Relevant Equations

lewis structure
VSEPR

I thought it was trigonal bipyramidal, with iodine forming 5 bonds with 5 fluorine atoms. Actually, iodine has another lone electron pair, making it square planar.

Is there a reason why iodine has another lone pair when it has already exceeded the octet rule? And how would I predict how many electron pairs a central atom exceeding the octet rule would have? Thank you.

 

[mjc123]

Iodine has 7 valence electrons. The fluorines contribute 1 each. So you have 12 electrons, or 6 pairs to arrange around the I atom.
And IF₅ is square pyramidal, not square planar.