http://www.ck12.org Chapter 9. Covalent Bonding
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The triiodide ion (Figure9.21) consists of three iodine atoms linked together by covalent bonds. Its overall charge
of 1- gives this structure 22 total valence electrons, resulting in a Lewis structure with three lone pairs on the central
iodine atom.
The five electron groups around the central atom give it a trigonal bipyramidal domain geometry, and all three
equatorial atoms have been replaced by lone pairs. The result is a linear ion—the central atom and the two axial
atoms.
FIGURE 9.21
Triiodide ion, I 3 −.AB
The bromine pentafluoride molecule (Figure9.22) has a central bromine atom, five single bonds to fluorine atoms,
and one lone pair.
The six groups of electrons around the central atom give it an octahedral domain geometry. Since all of the peripheral
atoms in an octahedral molecule are equivalent, any one of them could equally be replaced by the lone pair. The
resulting geometry is calledsquare pyramidal. A surface covering a square pyramidal molecule is a four sided
pyramid on a flat base.
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Xenon tetrafluoride (Figure9.23) has a Lewis structure consisting of four single bonds and two lone pairs on the
central xenon atom.