14.1 Shapes of Molecules and
Ions
More than 4 Charge Centers
• p-block elements
• Move electron(s) from s- or p-orbital into
unfilled low-energy d-orbital
For Example
• Phosphorous ([Ne] 3s23p3) 
([Ne] 3s13p33d1)
• PCl5
• Expanded Valence Shell
• Expanded Octet
• Usually with very polar molecules with small
atoms
– SF6, IF7
Molecular Shapes
5 Charge Centers
• PCl5
– Trigonal bipyramid, 90⁰ and 120⁰
• SF4
– See Saw
– *non bonded pairs in equatorial position
• Why?
• ICl3
– T-Shaped
• XeF2
– Linear
More Molecular Shapes
6 Charge Centers
-nonbonding pairs in axial position(s)
• SF6
– Octahedral
• BrF5
– Square pyramid
• XeF4
– Square planar
Resonance Structures
• Some molecules have more than one correct
Lewis structure
Resonance Structures
• AKA resonance Hybrids
• Extreme forms of the true structure
• True structure—somewhere
between the two
• Evidence for resonance comes from
bond length values
– Both bond lengths between the
oxygen atoms in ozone is somewhere
between an O-O and an O=O bond.
• Double-headed arrow indicates
resonance structures
Draw resonance structures for the
following…
• formate ion (CHO2-1)
• cyclobutadiene (C4H4):