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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
Chemical Bonding (II)Chemical Bonding (II)Chemical Bonding (II)Chemical Bonding (II)
1TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 1
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
Contents1. Basic Concepts.
a) Molecular parameters
b) Lewis Dot Symbols
2. The Covalent Bond
a) Polar Covalent Bond
b) Formal Charge
2TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 2
b) Formal Charge
c) Exceptions to the octet rule
3. The Valence-Shell Electron-Pair Repulsion Models
4. Bond theories
a) Valence Bond Theory. Hybridization of Atomic Orbitals
b) Molecular Orbital Theory
5. The Metallic Bond.
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
Bond Distance
-Average distance between the nuclei of two bonded atoms. -Factors affecting bond length:
a) Size of the bonded atoms (HI > HBr > HCl > HF)b) Multiplicity of bond (C-C > C=C )
1. BASIC CONCEPTS
A) Molecular Parameters
Image from:
3TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 3
-The internal angle between the orbitals containing electron pairs in the valence shell of the central atom in a molecule.
Bond Angle
Bond Enthalpy
It is the energy required to break one mole of bonds of a particular type of substancein gaseous state.
Image from: http://wikimediafoundation.org/wiki/File:Water_molecule_dimensions.svg
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
• Valence e- play a fundamental role in chemical bonding � the octet rule
• Chemical bond in terms of Lewis dot symbols
• ionic bond ���� e- transfer
• covalent bonds ���� e- sharing
1. BASIC CONCEPTS
B) Lewis dot symbols
4TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 4
C••
••
O•
••
•••N••
•
••
••
P •••
As••
•
••
F•
••
•••• Ne••
••••
••
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
In covalent bond atoms share electrons to complete their valence shell (i.e. to reach the gas noble configuration)
It forms between no-metalic elements.
2. THE COVALENT BOND
F••
•••
••F••
•••
••
• F••
••
••F••
•••
••Bond Pair
5TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 5
Coordinate covalent Bonds
The electron pair is provided by one of the atoms that form the covalent bond.
F••
••
••F••
••
••Lone Pairs
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
Polar Covalent Bonds
Electronegativity:describes the ability of an atom (or, more rarely, a functional group) to attract electrons (or electron density) towards itself in a covalent bond.
µ = Q x r
Dipole moment
H H
a) Non polar molecules b) Polar molecules
6TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 6
There is a shift of the electron density from H to F
µ = Q x r
r = distance between atomsQ = charge
Units Debye, D1 D = 3.33 10-30 C·m
F F
H F
Centre of positive charge
Centre of negative charge
Atomic nucleus
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General Chemistry General Chemistry
Diatomic molecules
Homonuclear molecules: H2, O2 y F2
Heteronuclear molecules HCl, CO y NO
Polarity of molecules
7TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 7
Polyatomic Molecules
Polarity depends on:
-Polarity of the chemical bonds
-Geometry
µ is the vectorial sum of the dipolar moments of the chemical bonds of the molecule.
CCl4A non-polar molecule
CHCl3A polar molecule
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
formal charge on an atom in a Lewis structure
=
total number of valence electrons in the free atom
-total number of nonbonding electrons
+1
2
total number of bonding electrons( )
Formal Charge
8TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 8
The sum of the formal charges of the atoms in a molecule or ion must equal thecharge on the molecule or ion.
Practice Exercise.
Write the Lewis structure for formaldehyde (CH2O) using the concept of formalcharge. Then compare your prediction with the real structure.
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
Exceptions to the Octet Rule
• Odd e- species.
• Incomplete octets.
••
••
•••N=O
9TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 9
• Expanded octets.
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
BeCl2
BF3
CH4
2
3
4
Linear
Trigonal planar
Tetrahedral
:
A
A: :
A:
:
AA) Molecules with no lone pairs
Electron pairs repel each otherwhether they are in chemical bonds(bond pairs) or unshared (lone pairs).Electron pairs assume orientationsabout an atom to minimizerepulsions.
No. of electron pairs or charge clouds
Distribution of the charge clouds(Molecular Shape)3. VSEPR MODEL
10TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 10
CH4
PCl5
SF6
4
5
6
Tetrahedral
Trigonal bipyramidal
Octahedral
AA
A
::
:
A
::
:::
:
A) Molecules with no lone pairson the central atom
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
B) Molecules with lone pairs on the central atom3. VSEPR MODEL
11TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 11
bond pairs vs.Bond pairs
Lone pairs vs.Lone pairs
lone pairs vs. bond pairs
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
B) Molecules with lone pairs on the central atom3. VSEPR MODEL
Number
of bond
pairs
(“x”)
Number of
Lone pairs of
electrons(“y”)
Number of
group of
electrons
(n = x+y)
VSEPR
Notation
(ABxEy)
Electron group
geometryExample
Ideal bond
angles Molecular geometry
2 0 2 AB2 Linear BeCl2 180º Linear
2 1 3 AB2E1 Trigonal planar SO2 120º Angular
12TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 12
4 0
4
AB4
Tetrahedral
CH4
109.5º
Tetrahedal
3 1 AB3E1 NH3 Piramidal
2 2 H2O AngularAB2E2
5 0
5
AB5
Trigonal
Bipyramidal
PCl5
90º; 120º
Trigonal pyramidal
4 1 AB4E1 SF4 Seesaw
3 2 ClF3 T- shapedAB3E2
2 3 AB2E3 XeF2 Linear
6 0
6
AB6
Octahedral
SF6
90º
Octahedral
5 1 AB5E1ICl5, BrF5XeOF4
Square pyramidal
4 2 AB4E2 XeF4;; ICl4- Square planar
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
Valence Bond Theory
• Atomic orbital overlap describes covalent bonding.
• Area of overlap of orbitals is in phase.
• A localized model of bonding.
4. BOND THEORIES
13TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 13
H2S
General Chemistry: Principles and Moderns Applications (R.H. Petrucci)
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
Hybridization of Atomic Hybridization of Atomic OrbitalsOrbitals
CH4
4. BOND THEORIES
Valence Bond Theory
14TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 14
-Promotion -Hybridization
Hybridization : term applied to the mixing ofatomic orbitals in a atom (i.e. linearcombination of the wavefunctions). Bond angle: 109.5 º
CH4 molecule
4 σσσσ bonds: C(sp 3)-H(1s)
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
BF3Orbital diagram B (ground state)
Promotion of one electron (2s ����2p)
(Excitation)
4. BOND THEORIES
Valence Bond Theory
15TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 15
Mixing of orbitals (2s & 2p)(Hybridization)
Bond angle: 120º
BF3 molecule
3 σσσσ bonds: B(sp 2)-F(2p)
3sp2 orbitals +
Unhybridised 2p
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
BeCl2
4. BOND THEORIES
Orbital diagram Be (ground state)
Promotion of one electron (2s ����2p)
(Excitation)
Valence Bond Theory
16TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 16
(Excitation)
Mixing of orbitals (2s & 2p)(Hybridization)
Bond angle: 180º
BeCl2 molecule
2 σσσσ bonds: Be(sp)-Cl(3p)
2sp orbitals+
2 Unhybridised 2p
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
Orbital diagram S (ground state)
Promotion of 2 electron (3s ����3p, 3d)
(Excitation)
3 3
3 3
4. BOND THEORIES
SF6
17TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 17
Mixing of orbitals (3s, 3p & 3d)(Hybridization)
sp3d2 orbitals SF 6 molecule
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General Chemistry General Chemistry
B) Geometry in acethylene molecule C 2H2
Hybridization of Atomic Orbitals. Geometry of Organic Molecules.
4. BOND THEORIES
Valence Bond Theory
18TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 18
C C HH
σBond C(sp)-H(1s)
ππππ Bonds C(2p)-C(2p)
σBond C(sp)-C(sp)
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
Hybridization Ideal bond angles Molecular geometry Stick and balls Model
sp 180º Linear
sp2 120º Trigonal
19TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 19
sp3 109.5º Tetrahedral
sp3d 90º; 120º Trigonal pyramidal
sp3d2 90ºOctahedral
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
4. BOND THEORIES
Molecular Orbital Theory
Explains the formation of the H-H bond in H2 molecule.
Description of the model:When the 1s wave functions of the two hydrogen atoms (H) are combined, one sigma(σ) bonding orbital (named σ1s ) is obtained. It is known as linear combination ofatomic orbitals (LCAO).
20TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 20
-The sum of the two 1s orbitals (one for each atom) yields the bonding orbital. Interms of wave mechanics, this corresponds to a constructive interaction .
-The difference of the two orbitals forms the antibonding orbital, s1s*, i.e. in termsof wave mechanics, this corresponds to a destructive interference.
atomic orbitals (LCAO).
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
4. BOND THEORIES
Molecular Orbital Theory
σ1sA + 1sB
•+
•+
• •+
Addition
Bonding interaction
Distance
21TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 21
1sA - 1sB
•+
•+
σ*
• •+ -
Substraction
Antibonding interaction
Distance
Distance
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
4. BOND THEORIES
Molecular Orbital Theory
22TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 22
Images from http://www.sparknotes.com/chemistry/bonding/molecularorbital/section1.html
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
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4. BOND THEORIES Molecular Orbital Theory
Molecular orbital for Homonuclear DiatomicMolecules of the second period (Li2 - N2)
Molecular orbital for Homonuclear DiatomicMolecules of the second period (O2 , F2, Ne2)
23TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 23
AtomicOrbitals(O)
AtomicOrbitals(O)Molecular
Orbitals(O2)
Image from http://www.sparknotes.com/chemistry/bonding/molecularorbital/section1.html
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
4. BOND THEORIES
Molecular Orbital Theory
24TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 24
Image from http://commons.wikimedia.org/wiki/File:MOdiagramCO.png
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
• First approach to explain the metallic bond: the electron sea model
– Nuclei are in a sea of electrons (the valence electrons)
5. THE METALLIC BOND
++ ++ ++ ++ ++ ++ ++ ++++ ++ ++ ++ ++ ++ ++ ++++ ++ ++ ++ ++ ++ ++ ++
25TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 25
– It explains metallic luster and malleability
Force applied
++ ++ ++ ++ ++ ++ ++ ++++ ++ ++ ++ ++ ++ ++ ++
+ + + + + + + ++ + + + + + + ++ + + + + + + +
+ + + + + + + ++ + + + + + + ++ + + + + + + +
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
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• Bond theories: the Band theory
– It is an extension of the MO theory
– “N” atoms give “N” orbitals with very close energies � a band is formed.
Band theory in alkaline metals Band theory in alkaline earths metals
5. THE METALLIC BOND
…
…
Li Li2 Li3 Li4 Lin (n ∼∼∼∼Nav)
Energy
Energy
band
26TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 26
Band theory in alkaline metals
Outer shell electron configuration: ns1
“N” orbitals, “N” levels � N/2 filled levels
Conduction band
Valence band
Conduction band
Valence band
Band theory in alkaline earths metals
Outer shell electron configuration: ns2
“N” orbitals, “N” levels � “N” filled levels“p” and “s” bands overlap in energy.
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5. THE METALLIC BOND
Band gap ∆∆∆∆Eg
Band gap ∆∆∆∆Eg
27TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 27
Elements of Group 14
Tin Germanium Silicon C (Diamond)Gap (eV): 0,08 0,72 1,11 6,0
a) Metal b) Metal c) Semiconductor d) Insulator
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UNIVERSIDAD CARLOS III DE MADRIDUNIVERSIDAD CARLOS III DE MADRID
General Chemistry General Chemistry
� R. H. Petrucci, W. S. Harwood, F. G. Herring, J. Madura. General Chemistry.Principles and Modern Applications. Prentice Hall, Ninth edition. Chapters 10-11.
� R. Chang. Chemistry. McGrawHill, Ninth edition. Chapters 9- 11.
Bibliography
28TopicTopic 44.. ChemicalChemical BondingBonding (II)(II) 28
� J. McMurry, R.C. Fay. Chemistry. Pearson, Fourth edition. Chapters 6, 7.