What is the molecular geometry of IF_5?

• A. Trigonal bipyramidal
• B. Square pyramidal
• C. Octahedral
• D. Tetrahedral

Answer: (B)

Verified step by step guidance

1. Determine the total number of valence electrons for the central atom, iodine (I). Iodine is in group 17, so it has 7 valence electrons.
2. Count the number of valence electrons contributed by the fluorine atoms. Each fluorine atom contributes 7 valence electrons, and there are 5 fluorine atoms, so total from fluorine is 5 × 7 = 35 electrons.
3. Add the valence electrons from iodine and fluorine: 7 (I) + 35 (F) = 42 valence electrons in total.
4. Draw the Lewis structure by placing iodine in the center and bonding it to 5 fluorine atoms with single bonds. Each bond uses 2 electrons, so 5 bonds use 10 electrons. Distribute the remaining electrons to satisfy the octet rule for fluorine atoms, and place any leftover electrons as lone pairs on iodine.
5. Determine the electron pair geometry and molecular geometry. Iodine has 5 bonding pairs and 1 lone pair (since 42 electrons correspond to 21 pairs, 5 bonding pairs use 10 electrons, 5 fluorines have full octets, and the leftover electrons form one lone pair on iodine). The electron pair geometry with 6 regions of electron density is octahedral, but the molecular geometry (considering the lone pair) is square pyramidal.