ElectronegativityEdward A. Mottel

Department of Chemistry

Rose-Hulman Institute of Technology

04/18/23

Electronegativity

Pauling’s concept Mulliken-Jaffé approach Electronegative orbitals & hybridizations Group electronegativity

04/18/23

ElectronegativityPauling

The power of an atom in a moleculeto attract electrons to itself.

Corollary: reluctance to release an electronto a more electronegative atom

Do the noble gases have electronegativity values?

H—Cl

H+Cl- H-Cl+

ionic resonance contributionswill stabilize the moleculeand make it more polar.

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ElectronegativityPauling

Compare the bond energies of H2, Cl2 and HCl.

H—Cl

H+Cl- H-Cl+

H2 432 kJ/mol

Cl2 240 kJ/mol

HCl 428 kJ/mol

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.

Cl—F

Cl+F- Cl-F+

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 sharean electron in its valence state with another atom.

Electronegativity iscalculated, not measured

One definition isEN = (IPv + EAv) / 2

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First Ionization Potential (IP)

H

He

Li

BeB

C

NO

F

Ne

Na

Mg

AlSi

PS

Cl

Ar

K

Ca

0

100

200

300

400

500

600

0 5 10 15 20Atomic Number

En

erg

y (k

cal/

mo

l)

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Electron Affinity

F(g) + e– F– (g)Na(g) + e– Na– (g)

lowest

highest

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Electronegativity

Li Be B

H

C N O F

Na Mg Al Si P S Cl

Rb Ca Sc BrGeZnGa As Se

Sr YZr Te ISn

1 32 4Electronegativity

Total energy includesionization or electron affinity

and promotion or hybridizationenergies.

ΧB°

ΧA°

Higher EN Lower EN

Orbital Electronegativity

Which molecule reacts with sodium metalin liquid ammonia?

ethane

ethylene

acetylene

Orbital Electronegativity

H - C - C - H

H

-

H

-H- H-

Carbonhybridization

sp3

CarbonEN

2.48

pKa

50

sp2 2.66 44C = CH H

H H

H - C C - H sp 2.99 25

Why does the electronegativity vary with hybridization?

Orbital Electronegativity

H - C - C - H

H

-

H

-H- H-

Carbonhybridization

sp3

CarbonEN

2.48

pKa

50

sp2 2.66 44C = CH H

H H

H - C C - H sp 2.99 25

For carbon: what is the s-orbital EN? p-orbital EN?

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-CΞN + H2O = NR

Substituent Effects and Electronegativity

HH

HC I

O H

FF

FC I

O H

HH

HC O H I

FF

FC H O I

Biphenylene

s & p-character?relativeacidity?

Group Electronegativity

O2+ [PtF6]

-O2 + PtF6

IE = 1.165 MJ·mol-1

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Where would hydrogen belong in the periodic table,if the table was organized by period and electronegativity?Hydrogen Is Electronegative

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Electronegativity

Li Be B

H

C N O F

Na Mg Al Si P S Cl

Rb Ca Sc BrGeZnGa As Se

Sr YZr Te ISn

1 32 4Electronegativity

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Dioxygenyl Hexafluoroplatinate(VI)

O2+ [PtF6]

-O2 + PtF6

IE = 1.165 MJ·mol-1What are the

ionization energiesof the noble gases? He = 2.37 MJ·mol-1

Ne = 2.08

Ar = 1.52

Kr = 1.35

Xe = 1.17