Transcript CH 1: Structure and Bonding

CH 1: Structure and Bonding
Renee Y. Becker
CHM 2210
Valencia Community College
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Organic Chemistry (present definition):
– the chemistry of carbon compounds
Organic Chemistry (Historical definition):
– Study of compounds extracted from living organisms,
study of compounds having the vital force
Vitalism:
– The belief that natural products needed a “vital force” to
create them
– In the 19th century experiments showed that organic
compounds could be synthesized from inorganic
compounds
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Friedrich Wohler
• In 1828, Wohler synthesized urea from
ammonium cyanate
O
+
NH4
OCN
-
heat
Ammonium cyanate (inorganic)
H2N
C NH2
urea
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Natural Product or Synthesized
• Plant-derived compounds and synthesized
compounds are identical (almost)
– You can tell them apart by 14C dating
– Synthesized compounds have a lower content
of radioactive 14C, their 14C has decayed over
time
– BUT, plant-derived compounds are recently
synthesized from CO2 in the air and therefore
have a higher content of radioactive 14C
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• Not all carbon compounds are organic
– Diamonds, graphite, CO2, NH4+ -OCN, Na2CO3
• Derived from minerals and have inorganic
properties
– Most of the millions of carbon compounds are
classified as organic
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Structure of the Atom
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Atomic
Orbitals
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Electronic Configurations
• Aufbau principle:
Place electrons in
lowest energy orbital
first.
• Hund’s rule: Equal
energy orbitals are
half-filled, then
filled.
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Increasing Energy
Core
[He]
[Ne]
[Ar]
[Kr]
[Xe]
[Rn]
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
7p
3d
4d 4f
5d 5f
6d
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Example 1: Electron Configuration
Draw electron configuration
1.
2.
3.
4.
5.
Cl
ClMg
Mg2+
Fe3+
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Bond Formation
• Ionic bonding: electrons are transferred.
• Covalent bonding: electron pair is shared.
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Lewis Structures
• Bonding electrons
• Nonbonding electrons or lone pairs
H
H C O
H
H
Satisfy the octet rule!
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Multiple Bonding
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Example 2: Lewis Dot Structures
Draw Lewis structures for the following
a)
b)
c)
d)
e)
NH3
CH3CH2F
CH3OCH3
BF3
C3H4
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Calculating Formal Charge
Formal charge =
(# own valence electrons in free atom)-(# own valence electrons in bonded atom)
3-
H O
H C C O
H
O
O
P
O
O
Put in formal charges
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Ionic Structures
+
H H
-
Cl
H C N H
H H
X
Na
O CH3
+
or Na
_
O CH3
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Example 3: Lewis Dot Structures
Draw the Lewis structure for the following
compounds or ions, showing formal charges
a)
b)
c)
d)
e)
(CH3)+
(CH3)NH4Cl
H3O+
(CH3)2NH2Cl
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Valence Bond Theory
1. Covalent bonds are formed by overlapping of
atomic orbitals, each of which contains one
electron of opposite spin.
2. Each of the bonded atoms maintains its own
atomic orbitals, but the electron pair in the
overlapping orbitals is shared by both atoms.
3. The greater the amount of orbital overlap, the
stronger the bond.
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Valence Bond Theory
• Linus Pauling: Wave functions from s
orbitals & p orbitals could be combined
to form hybrid atomic orbitals.
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• sp hybrid: acetylene
H
H
Bond angle 180
Electron pair Geometry linear
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•
sp2
hybrid: Ethylene
H
H
Bond angle 120 (varies)
Electron pair Geometry Trigonal Planar
H
H
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• sp2 hybrid (π bond):
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•
sp3
hybrid: Ethane
H
H
H
H
H
Bond angle 109.5 (varies)
Electron pair Geometry Tetrahedral
H
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sp3d hybrid:
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• sp3d2 hybrid:
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Example 4: Hybridization
What is the hybridization of the non-hydrogen
atoms?
H H H
1.
H
H
H
H
H
2.
H
H
3.
H
H
H
H
H
H
H
H
H
O
O
H
H
O
H
4.
H
H
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Molecular Orbital Theory
• The molecular orbital (MO) model provides a
better explanation of chemical and physical
properties than the valence bond (VB) model.
– Atomic Orbital: Probability of finding the
electron within a given region of space in an
atom.
– Molecular Orbital: Probability of finding the
electron within a given region of space in a
molecule.
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Molecular Orbital Theory
• Additive combination of orbitals (s) is
lower in energy than two isolated 1s orbitals
and is called a bonding molecular orbital.
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Molecular Orbital Theory
• Subtractive combination of orbitals (s*) is
higher in energy than two isolated 1s
orbitals and is called an antibonding
molecular orbital.
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Molecular Orbital Theory
• Molecular Orbital Diagram for H2:
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Molecular Orbital Theory
• Molecular Orbital Diagrams for H2– and
He2:
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Chemical Formulas
Full structural formula (no lone
pairs shown)
H O
H C C O H
H
Line-angle formula
Skeletal
O
OH
Condensed structural formula
CH3COOH
Molecular formula
C2H4O2
Empirical formula
CH2O
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Example 5: Chemical Formulas
Draw the condensed structural formula for the
following
O
1.
2.
OH
3.
4.
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Example 6: Chemical Formulas
Draw the skeletal structure
1. CH3(CH2)4CH3
2. CH3CH(CH3)2
3. CH3CH(CH3)CH(CH2CH3)CH2CH3
4. C(CH3)4
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