Learning Pyramid

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Learning Pyramid
Average retention rates for learning activities.
5 Lecture
10 Reading
20 Audio-Visual
30 Demonstration
50 Discussion Group
75 Practice by Doing
90 Teach Others/Immediate Use of Learning
National Training laboratories, Bethel ME.
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Chapter 1Structure and Bonding in Organic
Molecules

• Develop an accurate model for molecular bonding
• Electronic Structure of Atoms
• Electronic bonding of Molecules
• Lewis Dot Structures
• Valence Shell Electron Pair Repulsion (VSEPR)
  (Hybridization of atomic orbitals)
• Chemical Reactivity determined by Electronics and
  Molecular Shape

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Basics of Atom

• Protons (1 charge)
• Neutrons (no charge)
• Electrons (-1 charge)

Chemistry is the result of the addition or
removal of electrons
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Chemistry Based on Electron Exchange

• Potassium in Water

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Basics of Bonding

• Ionic Bonding
• Complete transfer of electron
• Ions held together by electrostatic attraction
• Covalent Bonding
• Sharing of electrons
• Atoms held together by attraction of proton to
  electron of another atom

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Quantum Mechanical Description of Electrons
Electrons are electromagnetic radiation in that
they are particle- like and wave-like
node
lobe
lobe
Very similar to a P orbital
(-)
()
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Atomic Orbitals - Described by the wavelike
nature of electrons that fill the volume of an
atomic orbital
Node is place of zero electron density
S-orbital nodes of 2s
Lobe
Node
e-
e-
e-
e-
e-
Atom in a Box
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S orbitals
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P orbitals
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Filling of Atomic Orbitals
The energy differences are directly related to
distance from the nucleus. Farther from the
nucleus is higher energy.
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Filling of orbitals (Electron Configuration or
Notation)
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Hybrid Orbitals - sp3
For Atomic Carbon 1s22s22p2
sp3 Hybridized Carbon
2p
2sp3
2s
1s
1s
Atoms bonded with other atoms have electrons in
the corresponding hybrid atomic orbitals sp,
sp2, sp3, and others
Isolated atoms have electrons in the
corresponding atomic orbitals s,p,d
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sp3 Orbital
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sp2 Orbital
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sp Orbital
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Electron repulsion of orbital lobes determines
bonding angles and the resulting molecular shape
180
(-)
(-)
trigonal planar
linear
120
109.5
tetrahedral
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Lewis Structures
1. Valence electrons - outermost shell of
electrons 2. Consider bond requirements of
atoms 3. Place lone pairs on central atom 4. C,
O, N, P, S, common central atoms -multiple
bonds possible 5. H, Cl, Br, I, F, common outer
atoms -single bonds possible
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Cross-Hatch Diagram Examples
For cross-hatch diagrams and many other instances
we use only the outer row of electrons or the
Valence electrons To construct a cross-hatch
diagram, we begin with a Lewis Structure Ethane,
Ethylene, Ethyne
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Types of Covalent Bonds
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Hybridization and Molecular Shape
of substituents or charge clouds
Bond angles
hybridization
geometry
180
sp
linear
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120
3
sp2
trigonal planar
109.5
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sp3
tetrahedral
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Methane
sp3 Hybridized - Tetrahedral shape
The last image in the animation depicts the
electrostatic potential surface, in other words,
the regions of positive () and negative (-)
charge
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Ethane
sp3 Hybridized - Tetrahedral shape
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Ethylene or ethene
sp2 Hybridized - Trigonal Planar shape
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Acetylene or Ethyne
sp Hybridized - Linear shape
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