The Structure and
Bonding of
IO3
An example of the use of Lewis Structures and
VSEPR Theory
Lecturer: Dr. Andreas Lemmerer
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IUPAC Nomenclature
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What type of compound is IO3- ?
According to IUPAC Nomenclature, it is a Polyatomic Ion.
Polyatomic ions contain more than one kind of atom.
In particular, it is a oxyanion that contains a nonmetal (I) and
oxygen.
Oxyanions (polyatomic anions containing oxygen) are named
with -ite or –ate as a base ending, depending on the number of
oxygen atoms bonded to the nonmetal.
IO3- has one atom of iodine and three atoms of oxygen.
Since iodine is a halogen and hence in the VIIA Group, the
oxyanion with three O atoms is given the -ate ending and hence
it’s name is IODATE.
cf. Group VA and VIA oxyanions with the -ate ending have four oxygen atoms
(phosphate (PO43-) , and group IVA oxyanions have three oxygen atoms (carbonate
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CO32-)
Structure and Bonding of
IO3
To determine the structure and the bonding of the iodate anion, we
will make use of the OCTET RULE:
The Octet Rule: Atoms tend to gain, lose, or share electrons until
they are surrounded by eight valence electrons.
Or:
In compound formation an atom gains or loses electrons, or shares
pairs of electrons, until its valence shell has eight electrons.
Atoms in the second period are limited to eight valence electrons,
and there are exceptions to the octet rule for atoms in the higher
periods, i.e. atoms from the 3rd period onwards can accommodate
more than an octet.
Note that O is in the second period and I is in the fifth period.
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Lewis Structures
- Lewis structures are representations of molecules showing all
electrons, bonding and nonbonding.
- Electron pairs shared between atoms are shown as a line “-” and
valence electrons around the atom as dots “•”.
- There is a sequence of five steps required to get to the correct
Lewis Structure of a compound.
Cl Cl
H F
H O
H
H N H
H
H
H C H
H
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Writing Lewis Structure for IO3-
IO3
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7 + 3(6) + 1 = 26
1. Find the sum of valence
electrons of all atoms in the
polyatomic ion or
molecule.
 If it is an anion, add one
electron for each negative
charge.
 If it is a cation, subtract one
electron for each positive
charge.
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Writing Lewis Structures
2. The central atom is
the least
electronegative
element that isn’t
hydrogen.
Keep track of the electrons:
26  6 = 20
Connect the outer
atoms to it by single
bonds.
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Writing Lewis Structures
3. Fill the octets of the
outer atoms.
Keep track of the electrons:
26  6 = 20  18 = 2
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Writing Lewis Structures
4. Fill the octet of
the central atom.
Keep track of the electrons:
26  6 = 20  18 = 2  2 = 0
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Writing Lewis Structures
• Then assign formal charges.
 For each atom, count the electrons in lone pairs and half the
electrons it shares with other atoms.
 Subtract that from the number of valence electrons for that
atom: The difference is its formal charge.
• The best Lewis structure…
 …is the one with the fewest charges.
 …puts a negative charge on the most electronegative atom.
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5. Arrange the pairs of
electrons until the
formal charges are at a
minimum, taking into
account the net charge
on the compound.
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Resonance of IO3
• One Lewis structure cannot accurately depict an anion such as
iodate.
• We use multiple structures, resonance structures, to describe the
molecule.
• The electrons are not localized, but rather are delocalized.
Experimental Observation: All three I-O bonds are approximately equivalent,
about 1.8 Å. I-O is about 2.2 Å and I=O 1.7 Å.
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The Shape of the Iodate Anion
• What Determines the Shape of
a Molecule?
• Simply put, electron pairs,
whether they are bonding or
nonbonding, repel each other.
• By assuming the electron pairs
are placed as far as possible
from each other, we can
predict the shape of the
molecule.
non-bonding electrons
bonding electrons
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Electron Domains
• This molecule has
four electron
domains, i.e. 4 areas
of electron-density
around I.
• We can refer to the electron
pairs (bonding/nonbonding) as electron
domains.
• In a double or triple bond,
all electrons shared between
those two atoms are on the
same side of the central
atom; therefore, they count
as one electron domain.
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Valence Shell Electron Pair Repulsion
VSEPR Theory
is based on the main
idea that “The best
arrangement of a
given number of
electron domains is
the one that
minimizes the
repulsions among
them.”
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Bonding vs Non-bonding domains
• Non-bonding e-pairs are physically
larger than bonding pairs.
• Therefore, their repulsions are
greater; this tends to decrease bond
angles in a molecule. The final
geometry or shape of the molecule
depends on the relative number of
bonding and non-bonding domains.
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Tetrahedral Electron Domain
• There are three molecular geometries according to
VSEPR Theory:
 Tetrahedral, if all are bonding pairs
 Trigonal pyramidal if one is a nonbonding pair
 Bent if there are two nonbonding pairs
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Finally, the Shape:
••
I
Trigonal Pyramidal:
O
O
O
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Tetrahedral Electron Domain
• There are three molecular geometries:
 Tetrahedral, if all are bonding pairs
 Trigonal pyramidal if one is a nonbonding pair
 Bent if there are two nonbonding pairs
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Trigonal Bipyramidal Electron Domain
• There are two distinct
positions in this
geometry:
 Axial
 Equatorial
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Trigonal Bipyramidal Electron Domain
Lower-energy conformations result from having
nonbonding electron pairs in equatorial, rather
than axial, positions in this geometry.
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Trigonal Bipyramidal Electron Domain
• There are four
distinct molecular
geometries in this
domain:
 Trigonal bipyramidal
 Seesaw
 T-shaped
 Linear
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Octahedral Electron Domain
• All positions are
equivalent in the
octahedral domain.
• There are three
molecular
geometries:
 Octahedral
 Square pyramidal
 Square planar
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