Electronegativity

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Electronegativity

• Edward A. Mottel
• Department of Chemistry
• Rose-Hulman Institute of Technology

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Electronegativity

• Paulings concept
• Mulliken-Jaffé approach
• Electronegative orbitals hybridizations
• Group electronegativity

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ElectronegativityPauling
The power of an atom in a molecule to attract
electrons to itself.
ionic resonance contributions will stabilize the
molecule and make it more polar.
Corollary reluctance to release an electron to a
more electronegative atom
Do the noble gases have electronegativity values?
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ElectronegativityPauling
Compare the bond energies of H2, Cl2 and HCl.
ionic resonance contributions
Which resonance structure is not very
important? Why?
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ElectronegativityPauling
Compare the bond energies of F2, Cl2 and ClF.
F2 155 kJ/mol
Cl2 240 kJ/mol
ClF 249 kJ/mol
ionic resonance contributions
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Electronegativity (EN)Mulliken-Jaffé
The tendency of an atom to gain or share an
electron in its valence state with another atom.
One definition is EN (IPv EAv) / 2
Electronegativity is calculated, not measured
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First Ionization Potential (IP)
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First Ionization Potential (IP)
Ionization energy (IE)
The trend is not perfect
Many inconsistencies can be associated with
electronic configuration and changes in orbital
spherical symmetry
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Electron Affinity
F(g) e F (g)
Na(g) e Na (g)
highest
lowest
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Electron Affinity and Electronegativity

• Increases
• from the bottom to the top
• from the left to the right

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Electronegativity
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Total energy includes ionization or electron
affinity and promotion or hybridization energies.
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Chlorine is the element with the
greatest electron affinity, why is fluorine is
the most electronegative element?
Is the electronegativity of an atom always the
same?
Is it possible for another species to be more
electronegative than fluorine?
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Fluorine is more electronegative than chlorine
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Orbital Electronegativity
Which molecule reacts with sodium metal in liquid
ammonia?
ethane
ethylene
acetylene
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Orbital Electronegativity
Carbon hybridization
Carbon EN
pKa
sp3
2.48
50
sp2
2.66
44
sp
2.99
25
H - C ? C - H
Why does the electronegativity vary with
hybridization?
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Orbital Electronegativity
Carbon hybridization
Carbon EN
pKa
sp3
2.48
50
sp2
2.66
44
sp
2.99
25
H - C ? C - H
For carbon what is the s-orbital EN? p-orbital
EN?
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Acidity-Basicity and Electronegativity
(CH3)3N H2O (CH3)3NH OH-
Kb 6.3 x 10-5
pyridine H2O pyridinium ion OH-
Kb 1.6 x 10-9
CH3-C?N H2O NR
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Substituent Effects and Electronegativity
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Biphenylene
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Group Electronegativity
IE 1.165 MJmol-1
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Hydrogen Is Electronegative
Where would hydrogen belong in the periodic
table, if the table was organized by period and
electronegativity?
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Electronegativity
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Dioxygenyl Hexafluoroplatinate(VI)
IE 1.165 MJmol-1
What are the ionization energies of the noble
gases?
He 2.37 MJmol-1
Ne 2.08
Ar 1.52
Kr 1.35
Xe 1.17