bonding
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Ionic Bonding
Resonance Structures
VSEPRBasic Shapes3-D NotationHybridization (Lab)
M olecular G eom etries
Octet Rule Polar M olecules
Lew is Structures Covalent Bonding
T ypes of Bonds
Chemical BondingChemical Bonding
Chlorides of Period 2compound LiCl BeCl2 BCl3 CCl4 NCl3 OCl2 Cl2
melting point
610 415 -107 -23 -40 -121 -102
Chlorides of Period 3compound NaCl MgCl2 AlCl3 SiCl4 PCl3 SCl6 Cl2
melting point
801 714 193 -69 -112 -51 -102
Let’s examine the melting point of compounds across two periods. What is the trend?
lowhigh
Conductivity - high Conductivity - low
Bonding Can we explain the melting point behavior across a period?
• involves the valence electrons or outermost shell (or highest shell) electrons
• for group A elements - the group number tells how many valence electrons
How many valence electrons on N?
Group 5A – 5 valence electrons
Bonding…
• Lewis dot structures show the valence electrons around at atom and for most molecules and compounds a complete octet for the elements
• most monatomic ions have an electron configuration of noble gases
N Al
F + e- F1s22s22p5 1s22s22p6 Ne
Write out the electron configuration for the following atoms and ions:
He
Ne
Ar
Kr
H-
Ca+2
O-2
Br-
Which noble gas is isoelectronic with each ion?
Na Cl
NaCl
+ -
electron transfer
and the formation of ions
This is the formation of an ionic bondionic bond.
ClCl
Cl2 This is the formation of a covalent bondcovalent bond.
sharing of a pair of electrons
and the formation of molecules
What about the distance between the atoms in a bond?
NaCl Na+ Cl- d = 281 pm
Cl2 Cl-Cl d = 199 pm
What property can be used to tell when a bond will ionic or covalent?
ionic
covalentHCl H2O CH4
MgO CaCl2 Na2S
Draw the Lewis dot structures for the following compounds:
Some exceptions to the Octet Rule
BF3
PCl5
SF6
Electronegativity
Chlorides of Period 2compound LiCl BeCl2 BCl3 CCl4 NCl3 OCl2 Cl2
EN 2.2 1.6 1.1 0.6 0 0.6 0
Chlorides of Period 3Compound NaCl MgCl2 AlCl3 SiCl4 PCl3 SCl6 Cl2
EN 2.2 1.9 1.6 1.3 1.0 0.6 0
large difference small difference
The electronegativity difference - EN = ENhigher – EN lower
Using electronegativities to determine bond type
EN > 1.7 ionic bond - transfer
EN < 1.7 covalent bond - sharing
So we have a range of electronegativity difference of 0 to 1.7 for sharing an electron pair.
Is the sharing of electrons in molecules always equal?
X Y EN = 0
X Y EN = 0.3
X Y EN = 0.6
X Y EN = 0.9
X Y EN = 1.2
ENY > ENX
Which element is more electronegative?
non-polar bond
incr
easi
ng p
olar
ity
of b
ond
polar bond
0 < EN < 1.7
Direction of electron migration
BF3 – a planar molecule
Ball & stick
BF
Space-filled
Electrostatic potential maps
top side
negative
positive
Spartan ‘02
2.0
4.0
More sharing examples
O2
N2
O O
N N
O O O O
N N N N N N
double bond (2 pairs)
triple bond (3 pairs)
Share until octet is complete.
octet complete
Bond Energy
F2 single bond BE = 142 kJ/mole
O2 double bond BE = 494
N2 triple bond BE = 942
X2 + energy X + X
incr
easi
ng b
ond
stre
ngth
Is breaking a bond an endothermic or exothermic process?
http://wulfenite.fandm.edu/Data%20/Table_6.html
NH3
NH
H
H
NH
H
HH+
NH4+ NH3 + H+ NH4
+
coordinate covalent bond(the pair of electrons from
the same atom)
normal covalent bond(each atom supplies an
electron)
Some more sharing examples
Type of bond? – I, PC, or NC
TiO2 CH4 NaI
CS2 CO2 KCl
AlCl3 CsF HBr
Using the EN trends to predict bond type
105
Db107
Bh
Increasing EN
Incr
easi
ng E
N
NO RbF FeS H2SModified from http://www.cem.msu.edu/~djm/cem384/ptable.html
Draw the Lewis dot structures
CO2
H3O+ CO
H2CO
NH2-
HCN
(C in center)
Show the direction of electron migration ( ) in the following.
C – H
H – F
C = O
C – Cl
Rank the bond polarity (1-most … 3-least)
As-H N-H P-H
Here is the electrostatic potential map for H2CO.
Show the electron migration on this planar molecule.
C OH
H
How is this molecule different than BF3?
blue – positive red - negative
ionic covalent
valence electrons
Comparison of Bonding Types
sharing of electrons
transfer of electrons
ions molecules
EN > 1.7 EN < 1.7
high mp low mp
molten salts conductive
non-conductive
Bonding spectrum100% covalent 100% ionic
A+ B-A B A B
Increasing EN
Increasing polarity Transfer
• Chemical bond: attractive force holding two or more atoms together.
• Covalent bond results from sharing electrons between the atoms. Usually found between nonmetals.
• Ionic bond results from the transfer of electrons from a metal to a nonmetal.
• Metallic bond: attractive force holding pure metals together.
Chemical Bonds, Lewis Symbols, and the Octet RuleChemical Bonds, Lewis Symbols, and the Octet Rule
Figure 8.3: Ionic BondingFigure 8.3: Ionic Bonding
Figure 8.5: Covalent BondingFigure 8.5: Covalent Bonding
Chemical BondsChemical Bonds
Bond Type Single Double Triple
# of e’s 2 4 6
Notation — =
Bond order 1 2 3
Bond strength
Increases from Single to Triple
Bond length Decreases from Single to Triple
Strengths of Covalent BondsStrengths of Covalent Bonds
Lewis Symbols
Chemical Bonds, Lewis Symbols, and the Octet RuleChemical Bonds, Lewis Symbols, and the Octet Rule
The Octet Rule• All noble gases except He has an s2p6 configuration. • Octet rule: atoms tend to gain, lose, or share electrons
until they are surrounded by 8 valence electrons (4 electron pairs).
• Caution: there are many exceptions to the octet rule.
Chemical Bonds, Lewis Symbols, and the Octet RuleChemical Bonds, Lewis Symbols, and the Octet Rule
Bond Polarity and ElectronegativityBond Polarity and Electronegativity
Electronegativity• Electronegativity: The ability of one atoms in a
molecule to attract electrons to itself.• Pauling set electronegativities on a scale from 0.7 (Cs) to
4.0 (F).• Electronegativity increases
• across a period and
• down a group.
Figure 8.6: Electronegativities of ElementsFigure 8.6: Electronegativities of Elements
Electronegativity
Bond Polarity and ElectronegativityBond Polarity and Electronegativity
Figure 8.7: Electronegativity and Bond Polarity• There is no sharp distinction between bonding types.• The positive end (or pole) in a polar bond is represented
+ and the negative pole -.
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Drawing Lewis StructuresDrawing Lewis Structures
Follow Step by Step Method (See Ng Web-site)
1. Total all valence electrons. [Consider Charge]
2. Write symbols for the atoms and guess skeleton structure [ define a central atom ].
3. Place a pair of electrons in each bond.
4. Complete octets of surrounding atoms. [ H = 2 only ]
5. Place leftover electrons in pairs on the central atom.
6. If there are not enough electrons to give the central atom an octet, look for multiple bonds by transferring electrons until each atom has eight electrons around it.
HyperChemCyberChem (Lewis) video
Exceptions to the Octet RuleExceptions to the Octet Rule
Central Atoms Having Less than an Octet• Relatively rare.• Molecules with less than an octet are typical for
compounds of Groups 1A, 2A, and 3A.
• Most typical example is BF3.
• Formal charges indicate that the Lewis structure with an incomplete octet is more important than the ones with double bonds.
Exceptions to the Octet RuleExceptions to the Octet Rule
Central Atoms Having More than an Octet• This is the largest class of exceptions.• Atoms from the 3rd period onwards can accommodate
more than an octet.• Beyond the third period, the d-orbitals are low enough in
energy to participate in bonding and accept the extra electron density.
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• There are five fundamental geometries for molecular shape:
Molecular Shapes: VSEPRMolecular Shapes: VSEPR
Molecular Shapes – 3D NotationsMolecular Shapes – 3D Notations
VSEPR (Ballons)-Movie Clip
Figure 9.3
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Summary of VSEPR Molecular ShapesSummary of VSEPR Molecular Shapese-pairs Notation Name of VSEPR shape Examples
2 AX2 Linear HgCl2 , ZnI2 , CS2 , CO2
3 AX3 Trigonal planar BF3 , GaI3
AX2E Non-linear (Bent) SO2 , SnCl2
4 AX4 Tetrahedral CCl4 , CH4 , BF4-
AX3E (Trigonal) Pyramidal NH3 , OH3-
AX2E2 Non-Linear (Bent) H2O , SeCl2
5 AX5 Trigonal bipyramidal PCl5 , PF5
AX4E Distorted tetrahedral
(see-sawed)
TeCl4 , SF4
AX3E2 T-Shaped ClF3 , BrF3
AX2E3 Linear I3- , ICl2
-
6 AX6 Octahedral SF6 , PF6-
AX5E Square Pyramidal IF5 , BrF5
AX4E2 Square Planar ICl4- , BrF4
-See Ng Web-siteHyperChem CyberChm Gems
Examples: VSEPR Molecular Shapes - IExamples: VSEPR Molecular Shapes - I# electron pairs on Central Atom A
Notation Example Lewis VSEPR & Name of Shape
2AX2
2 bp on A
3
AX3 3 bp on A
AX2E2 bp and 1 lp on A
Examples: VSEPR Molecular Shapes – I – F08Examples: VSEPR Molecular Shapes – I – F08
Examples: VSEPR Molecular Shapes - IIExamples: VSEPR Molecular Shapes - II# electron pairs on Central Atom A
Notation Example Lewis VSEPR & Name of Shape
4
AX4
4 bp on A
AX3E 3 bp and 1 lp on A
AX2E2
2 bp and 2 lp on A
Examples: VSEPR Molecular Shapes – II – F08Examples: VSEPR Molecular Shapes – II – F08
Examples: VSEPR Molecular Shapes - IIIExamples: VSEPR Molecular Shapes - III# electron pairs on Central Atom A
Notation Example LewisVSEPR & Name of Shape
5
AX5 5 bp on A
AX4E4 bp and 1 lp on A
AX3E2
3 bp and 2 lp on A
AX2E3
2 bp and 3 lp on A
Examples: VSEPR Molecular Shapes - IVExamples: VSEPR Molecular Shapes - IV# electron pairs on Central Atom A
Notation Example Lewis VSEPR & Name of Shape
6
AX6
6 bp on A
AX5E 5 bp and 1 lp on A
AX4E2
4 bp and 2 lp on A
The Effect of Nonbonding Electrons
• By experiment, the H-X-H bond angle decreases on moving from C to N to O:
• Since electrons in a bond are attracted by two nuclei, they do not repel as much as lone pairs.
• Therefore, the bond angle decreases as the number of lone pairs increases
VSEPR ModelVSEPR Model
104.5O107O
NHH
HC
H
HHH109.5O
OHH
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Figure 9.10: Shapes of Larger Molecules
• In acetic acid, CH3COOH, there are three central atoms.
VSEPR ModelVSEPR ModelHyperChem
Shapes of Larger Molecules• In glycine (simplest amino acid), NH2CH2CO2H, there are four possible central atoms.
• Draw the Lewis Structure and the 3D VSEPR Molecular Geometry for glycine. Indicate the name of the shape for all possible central atoms, including estimation of bond angles.
• Hint 1: Designate the 2nd carbon in the formula as the central atom in skeleton structure.
• Hint 2: The acid portion of glycine is the same as that of acetic acid.
Lewis-VSEPR HW assigned 10/29/10 . Due 11/1/10.Lewis-VSEPR HW assigned 10/29/10 . Due 11/1/10.Lewis-VSEPR HW assigned 10/29/10 . Due 11/1/10.Lewis-VSEPR HW assigned 10/29/10 . Due 11/1/10.
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Solution Key
Figure 8.10: Drawing Lewis StructuresFigure 8.10: Drawing Lewis Structures
Resonance Structures
Figure 9.12
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Figure 9.11: Molecular Shape and Molecular PolarityFigure 9.11: Molecular Shape and Molecular Polarity
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Figure 9.13: Molecular Shape and Molecular PolarityFigure 9.13: Molecular Shape and Molecular Polarity
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• Lewis structures and VSEPR do not explain why a bond forms.
• How do we account for shape in terms of quantum mechanics?
• What are the orbitals that are involved in bonding?• We use Valence Bond Theory:
• Bonds form when orbitals on atoms overlap.
• There are two electrons of opposite spin in the orbital overlap.
Covalent Bonding and Orbital OverlapCovalent Bonding and Orbital Overlap
Gems - Movie Clip
Figure 9.14: Covalent Bonding and Orbital OverlapFigure 9.14: Covalent Bonding and Orbital Overlap
• To determine the electron pair geometry:• draw the Lewis structure,
• count the total number of electron pairs around the central atom,
• arrange the electron pairs in one of the above geometries to minimize e-e repulsion, and count multiple bonds as one bonding pair.
VSEPR Model (Figure 9.6)VSEPR Model (Figure 9.6)
VSEPR VSEPR ModelModel
Drawing Lewis StructuresDrawing Lewis Structures
Formal Charge• Consider:
• For C: • There are 4 valence electrons (from periodic table).
• In the Lewis structure there are 2 nonbonding electrons and 3 from the triple bond. There are 5 electrons from the Lewis structure.
• Formal charge: 4 - 5 = -1.
C N
Drawing Lewis StructuresDrawing Lewis Structures
Formal Charge• Consider:
• For N:• There are 5 valence electrons.• In the Lewis structure there are 2 nonbonding electrons and 3
from the triple bond. There are 5 electrons from the Lewis structure.
• Formal charge = 5 - 5 = 0.• We write:
C N
C NCyberChm Gems
Ionic Bonding
Resonance Structures
VSEPRBasic Shapes3-D NotationHybridization (Lab)
M olecular G eom etries
Octet Rule Polar M olecules
Lew is Structures Covalent Bonding
T ypes of Bonds
Chemical BondingChemical Bonding
Lewis
AXE notation
VSEPR shapes
Polarity