Transcript Expanded Valence and Resonance

Drill #1 – Jan. 7, 2014
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Draw the Lewis Structures for CF4, NH3,
CO2, H20, H2CO and C2H2 on your
Hybridization Worksheet.NO2-1
Objectives
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SWBAT write Lewis structures for molecules
that are exceptions to the octet rule.
SWBAT explain resonance and write
resonance structures.
Apply hybridization to determining the orbital
shape of a molecule.
Announcement
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Wed/Thurs – quiz (~30 pts)
Review WS – posted on webpage
Turn in STEM redos
January 23 – STEM Fair Poster Due
MidTerm Exam Schedule
Tues, 1/14
Full Day – Period 1 Exam during the
regular time pd
Wed, 1/15
Day 2 -Examinations – Periods 2 & 3
Schools close 3 hours early.
Thurs, 1/16
Day 3 -Examinations – Periods 4A & 4B
Schools close 3 hours early.
Fri, 1/17
Day 4 -Examinations – Periods 5 & 6
Schools close 3 hours early.
Expanded Valence, Resonance
& Hybridization
Exceptions to the Octet Rule
1) Molecules with an odd # of electrons
2) Molecules in which an atom has less
than an octet of electrons
3) Molecules in which an atom has more
than an octet of electrons
4) Molecules that only need two valence
electrons to be stable.
Exceptions to the Octet Rule
1) Molecules with an odd number of valence
electrons – Example: NO
Exceptions to the Octet Rule
2) Less than an Octet
Exceptions to the Octet Rule
3) More than 8 valence electrons; Occur in
atoms that have the 3d sublevel available for
bonding
Exceptions to the Octet Rule
4) Atoms that only have two valence
electrons
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H, He, Li, and Be
Stable with only two valence electrons in
their s sublevel
“Expanded Valence”
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Some molecules or ions have an “expanded
valence” where there are more than 8 electrons
in the valence shell of an atom (in these cases,
bonding involves electrons in the d orbitals as
well as in the s and p orbitals)
You know you have expanded valence if the
bonding electrons are less than the bonds
necessary to connect everything!
Example: XeF4
Expanded Valence: XeF4
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Only third-period (or lower) elements
are capable of having an expanded
valence; second period elements can
not exceed the octet
Why??
Practice Problems
Draw Lewis structures for the following:
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ICl4-
Trigonal Bipyramidal
Five bonds around a central atom. (will
only occur in the case of an expanded
octet)
Bond angle = 120° & 90°
Octahedral
Six bonds around a central atom. (will
only occur in the case of an expanded
octet)
Bond angle = 90°
Less than an Octet
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Situations where there are fewer than
an octet of electrons around an atom
are rare
Boron does not have an octet, only 6
valence electrons
Example: BF3
Lewis Structure for BF3
Resonance
Resonance refers to bonding in molecules or
ions that cannot be correctly represented by
a single Lewis structure
 If two resonance structures exist for a
molecule, the “true” structure is best
represented by the average of the two
resonance hybrids
Example: O3

Resonance Forms of Ozone
Drill #2
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1/6 & 7/14
Take out Chemical Bonding: 9:1 Bonding of Atoms.
Determine the type of bond (polar covalent, nonpolar
covalent, ionic) that exists between the following
atoms:
 H and S
 Mg and F
 P and Cl
 I and I
 Use old WS for electronegativity values and the
following slide for electronegativity ranges.
Bond Type by Electronegativity
Electronegativity
Difference
Bond Type
<0.4
nonpolar covalent
Between 0.4 & 1.7
polar covalent
>1.7
ionic
Drill #2
1/6 & 7/14
Answers:
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H and S – nonpolar covalent (~0.38)
Mg and F – ionic (~2.67)
P and Cl – polar covalent (~0.97)
I and I – nonpolar covalent (0.00)
 Use old WS for electronegativity values and the
following slides for electronegativity ranges.
Objectives
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Apply hybridization to determining the orbital
shape of a molecule.
Organic chemistry intro…
Hybridization
Hybridization
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Each atom has their own orbitals (we know
orbital diagrams)…BUT when atoms are
combined in a molecule, their orbitals combine
or OVERLAP to make molecular orbitals
These are orbitals that apply to the entire
molecule that hold 2 electrons
What is hybridization?
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Atoms use their valence electrons to form
bonds. But how is it that they form bonds of
equal energy when some of the electrons come
from the s orbital and some come from the p
orbital??
Hybrid orbitals are orbitals of equal energy
(between the energy of s & p orbitals) produced
by the combination of two or more orbitals on
the same atom.
Hybridization
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An atom in a molecule may adopt a different
set of atomic orbitals (called hybrid orbitals)
than those it has in the free state.
The hybridization of a particular molecule is
determined by the central atom. We only
need to worry about it’s valence electrons.
Your Hybridization Options:
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sp
sp2
sp3
sp3d
sp3d2
sp3d3
Consider CH4
Carbon has 4 valence electrons
1s2 2s2 2p2
2 of the electrons are in the s orbital
and 2 are in the p orbital.
s & p have different shapes and
different amounts of energy.
Consider CH4
To create 4 equal bonds, carbon’s one
2s orbital and three 2p orbitals fuse into
4 new identical orbitals called sp3.
2p
2s
Hybridization
sp3
Hybridization
BCl3
Look at B
Write the orbital diagram for B
Promote electrons
http://www.dlt.ncssm.edu/tiger/diagrams/moleculargeometry/BCl3_Hybrid.gif
What type of hybridization does BF3 have?
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1s2 2s2 2p1
2p
Empty
hybridized
orbitals are
dropped
Hybridization
sp3
2s
sp2
So sp3
becomes
sp2
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What type of hybridization does H2O
have?
O  1s2 2s2 2p4
2p
2s
Hybridization
sp3