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Today’s Quiz
1. What is ground-state electron configuration?2. Define valence electrons and valence shell.3. Explain the exceptions to the octet rule.4. Define Electronegativity.5. What is the difference between a nonpolar covalent bond and a polar
covalent bond.6. What are the 3 molecular shapes?7. What is a hybrid orbital?
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Chapter 1: Covalent Bonding and Shapes of Molecules
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1.1 How do we describe the electronic structure of Atoms?
1.2 What is the Lewis Model of Bonding?
1.3 How do we Predict Bond Angles and the Shapes of Molecules?
1.4 How do we predict if a molecule is polar or non-polar?
1.5 What is resonance?
1.6 What is the Molecular orbital model of covalent bonding?
1.7 What are the Functional Groups? (Group Presentation)
Chapter 1: Covalent Bonding and Shapes of Molecules
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Quantum Numbers and Atomic OrbitalsAn atomic orbital is specified by four quantum numbers.
n the principal quantum number - a positive integer, indicates the relative size of the orbital or the distance from the nucleus
l the angular momentum quantum number - an integer from 0 to n-1, related to the shape of the orbital
ml the magnetic moment quantum number - an integer from -l to +l,
orientation of the orbital in the space around the nucleus 2l + 1
Schrodinger Wave Equation
ms spin quantum number
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Table 7.2 The Hierarchy of Quantum Numbers for Atomic Orbitals
Name, Symbol(Property) Allowed Values Quantum Numbers
Principal, n(size, energy)
Angular momentum, l
(shape)
Magnetic, ml
(orientation)
Positive integer(1, 2, 3, ...)
0 to n-1
-l,…,0,…,+l
1
0
0
2
0 1
0
3
0 1 2
0
0-1 +1 -1 0 +1
0 +1 +2-1-2
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Y = fn(n, l, ml, ms)
spin quantum number ms
ms = +½ or -½
Schrodinger Wave Equation
ms = -½ms = +½
7.6
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Electron configuration is how the electrons are distributed among the various atomic orbitals in an atom.
1s1
principal quantumnumber n
angular momentumquantum number l
number of electronsin the orbital or subshell
Orbital diagram
H
1s1
7.8
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Order of orbitals (filling) in multi-electron atom
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s7.7
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Ionic Bond
• Is the electrostatic force that holds ions together in an ionic compound
• The metal gives the electrons to the non metal
• Cation is the metal• Anion is the non metal
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The Covalent Bond
• A bond in which two electrons are shared by two atoms.
• Only in covalent compounds
• Non metal and non metal
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The Covalent Bond
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The Covalent Bond
• Pairs of valence electrons that are not involved in covalent bond formation are called: Lone pairs
• We can only draw Lewis structures for compounds that have covalent bonds
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Lewis Dot Symbols
Consists of the symbol of an element and one dot for each valence electron in an atom of the element.Note that (except helium) the number of valance electrons each atom has is the same as the group number of the element.
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Lewis Structures
• Is a representation of covalent bonding in which shared electron pairs are shown either as lines or as pairs of dots between two atoms, and lone pairs of dots on individual atoms
• Only valence electrons are shown in a Lewis structure
• Valence electrons: Electrons in the valence (outermost) shell of an atom.
• Valence shell: The outermost electron shell of an atom.
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Electronegativity
• The ability of an atom to attract toward itself the electrons in a chemical bond
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Electronegativity
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I. Lewis StructuresB. Ionic, covalent, and polar bonds
H—HC = 2.1 2.1
DC = 0 equal sharing of electronsCl—Cl = nonpolar covalent bond
C = 3.0 3.0
H—Cl DC = 0.9 unequal sharing of electronsC = 2.1 3.0 = polar covalent bond
Na+Cl– DC = 2.1 transfer of electronsC = 0.9 3.0 = ionic bond
generally: when DC <0.5 non-polar covalent 0.5<DC = 1.9 polar covalent
> 1.9 ionic
d+ d–
nonmetal+
nonmetal
metal+
nonmetal
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Polar and Nonpolar Molecules
• A molecule will be polar if:
• 1. It has polar bonds.
• 2. The center of partial positive charge lies at a different place within the molecule than the center of partial negative charge.
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The "best" Lewis structure for NO3-
• 1. Determine the total number of valence electrons in a molecule
• Draw a skeleton
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• Of the 24 valence electrons in NO3-, 6 were required
to make the skeleton. Consider the remaining 18 electrons and place them so as to fill the octets of as many atoms as possible
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• Are the octets of all the atoms filled? If not then fill the remaining octets by making multiple bonds
• Check that you have the lowest FORMAL CHARGES possible for all the atoms, without violating the octet rule; (valence e-) - (1/2 bonding e-) - (lone electrons).
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The Octet Rule
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Exceptions to the Octet Rule
• The expanded octet– Atoms in the 2nd period (that
are in families 3A-7A) cannot have more than 8 valance electrons around the central atom
– Atoms of elements in and beyond the 3rd period (that are in families 3A-7A) form some compound in which more than 8 electron surround the central atom
• Odd- electron molecules– Some molecules contain an
odd number of electrons.– We need an even number
of electron for complete pairing the octet rule clearly cannot be satisfied with all the atoms in any of these molecules
• Incomplete octet– The number of electrons
surrounding the central atom in a stable molecule is fewer than eight
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Figure 2.10 The modern periodic table.
+1+2 +3 -3 -2 -1
0
NC
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The Concept of Resonance
• Resonance means the use of two or more Lewis structures to represent a particular molecule
• Resonance structure, is one of two or more Lewis structures for a single molecule that cannot be represented accurately by only one Lewis structure
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E. Resonance structures-two or more equivalent Lewis structures-nuclei remain in fixed positions, but electrons arranged differently
HCO2-
H CO
OH C
O
O= H C
O
O
½ -
½ -
1.5 bond order•neither of these accurately describes the formate ion•actual species is an average of the two (resonance hybrid)
•Resonance hybrid: A molecule or ion that is best described as a composite of a number of contributing structures.
delocalizedelectrons
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I. Lewis StructuresE. Resonance structures
=CO
NH2
CH3 CNH2
OCH3 CH3 C
O
NH2+
-
more stablemajor contributor
less stableminor contributor
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x
y
z
90o
90o
2pz
2py2px
Shapes of 2px, 2py, 2pz atomic orbitals and their orientation in space
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methane
H
H
HH
109.5o
ethene
C C
H H
HH
120o
ethyne
C CH H
180o
tetrahedralTrigonal planar or pyramidal
linear
Region of electron density around the central atom.
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Sigma bond is covalent bond in which the overlap of atomic orbitals is concentrated along the bond
axis
Hybrid orbital an orbital produced from the combination of two or more atomic orbitals.
Pi bond a covalent bond formed by the overlap of parallel p orbitals.
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Why does hybridization occur?
• In chemistry hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals suitable for the qualitative description of atomic bonding properties.
• Hybridized orbitals are very useful in the explanation of the shape of molecular orbitals for molecules. It is an integral part of organic chemistry.
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• Sp3 hybrid orbitals – Bond angles of approximately 109.5o
• Four sigma bonds
• 4 groups bonded to carbon
Sp2 hybrid orbitals – Bond angles of approximately 120o
• Three sigma bonds and one pi bond
• 3 groups bonded to carbon
• Sp hybrid orbitals – Bond angles of approximately 180o • Two sigma bonds and two pi bonds
• 2 groups bonded to carbon
tetrahedral
Trigonal planar
linear
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III. Valence Bond ModelA. Hybrid atomic orbitals
1. sp3 hybridization
CH4 facts: tetrahedral,4 equivalent bondsC
H
HH
H
C2s
2ppromoteelectron 2p
2s
hybridize
sp3
hybrida.o.s
sp3 hybrid a.o.s:
C(sp3)tetrahedral (sp3
C + 1sH)
4HC
H
HH
H
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III. Valence Bond ModelB. Hybrid atomic orbitals
1. sp3 hybridization
C N O
CN
HH
H
HH
CC
H
HH
H
HH C
OH
H
HH
(sp3C + sp3
C) (sp3C + sp3
N) (sp3C + sp3
O)
lone pairsin sp3 a.o.s
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III. Valence Bond ModelB. Hybrid atomic orbitals
2. sp2 hybridizationC2H4 facts: all six atoms lie
in same planeC CH
H
H
H
trigonal planar = sp2
2psp2
C Csp2
2p
H1s 1s
H H1s 1s
H
C CH H
H H
2p
(sp2C + 1sH)
(sp2C + sp2
C)
overlapp orbitals C C
H H
H H
bond
all atoms coplanarfor p orbital overlap
= C C
H
H
H
H
double bond =1 bond +1 bond
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III. Valence Bond ModelB. Hybrid atomic orbitals
2. sp2 hybridization
C O
(sp2C + sp2
C) + (sp2C + sp2
O) +
lone pairsin sp2 a.o.s
C CHH
HHC O
H
H
C C
H
H
H
H
C
H
H
O
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III. Valence Bond ModelB. Hybrid atomic orbitals
3. sp hybridization
C2H2 facts: linear = spH C C H
2psp
C Csp
2p
H1s 1s
H
C C HH
2p
(spC + 1sH)
(spC + spC)
C CH H
2 bonds
= C CH H
triple bond =2 bonds +1 bond
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III. Valence Bond ModelB. Hybrid atomic orbitals
3. sp hybridization
N
(spC + spN) + 2
lone pairin sp a.o.
C NH
H C N