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

6/14/2015 Electronegativity  Pauling’s concept  Mulliken-Jaffé approach  Electronegative orbitals & hybridizations  Group electronegativity

6/14/2015 Electronegativity Pauling The power of an atom in a molecule to attract electrons to itself. Corollary: reluctance to release an electron to a more electronegative atom Do the noble gases have electronegativity values? H—Cl H + Cl - H - Cl + ionic resonance contributions will stabilize the molecule and make it more polar.

6/14/2015 Electronegativity Pauling Compare the bond energies of H 2, Cl 2 and HCl. H—Cl H + Cl - H - Cl + H kJ/mol Cl kJ/mol HCl 428 kJ/mol ionic resonance contributions Which resonance structure is not very important? Why?

6/14/2015 Electronegativity Pauling Compare the bond energies of F 2, Cl 2 and ClF. Cl—F Cl + F - Cl - F + F kJ/mol Cl kJ/mol ClF 249 kJ/mol ionic resonance contributions

6/14/2015 Electronegativity (EN) Mulliken-Jaffé The tendency of an atom to gain or share an electron in its valence state with another atom. Electronegativity is calculated, not measured One definition is EN = (IP v + EA v ) / 2

6/14/2015 First Ionization Potential (IP) H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Atomic Number Energy (kcal/mol)

6/14/2015 First Ionization Potential (IP) lowest highest Ionization energy (IE) The trend is not perfect Many inconsistencies can be associated with electronic configuration and changes in orbital spherical symmetry

6/14/2015 Electron Affinity F(g) + e –  F – (g) Na(g) + e –  Na – (g) lowest highest

6/14/2015 Electron Affinity and Electronegativity  Increases from the bottom to the top from the left to the right

6/14/2015 Electronegativity LiBeB H CNOF NaMgAlSiPSCl RbCaSc BrGeZnGaAsSe SrYZr TeISn 1324 Electronegativity

Total energy includes ionization or electron affinity and promotion or hybridization energies.

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?

Fluorine is more electronegative than chlorine

ΧB°ΧB° ΧA°ΧA° Higher ENLower EN

Orbital Electronegativity Which molecule reacts with sodium metal in liquid ammonia? ethane ethylene acetylene

Orbital Electronegativity H - C - C - H H - H - H - H - Carbon hybridization sp 3 Carbon EN 2.48 pK a 50 sp C = C HH HH H - C  C - H sp Why does the electronegativity vary with hybridization?

Orbital Electronegativity H - C - C - H H - H - H - H - Carbon hybridization sp 3 Carbon EN 2.48 pK a 50 sp C = C HH HH H - C  C - H sp For carbon: what is the s-orbital EN? p-orbital EN?

Acidity-Basicity and Electronegativity (CH 3 ) 3 N + H 2 O = (CH 3 ) 3 NH + + OH - K b = 6.3 x pyridine + H 2 O = pyridinium ion + OH - K b = 1.6 x CH 3 -C Ξ N + H 2 O = NR

Substituent Effects and Electronegativity H H H CI OH F F F CI OH H H H COH I F F F CH OI

Biphenylene s & p-character? relative acidity?

Group Electronegativity O 2 + [PtF 6 ] - O 2 + PtF 6 IE = MJ·mol -1

6/14/2015 Where would hydrogen belong in the periodic table, if the table was organized by period and electronegativity? Hydrogen Is Electronegative

6/14/2015 Electronegativity LiBeB H CNOF NaMgAlSiPSCl RbCaSc BrGeZnGaAsSe SrYZr TeISn 1324 Electronegativity

6/14/2015

Dioxygenyl Hexafluoroplatinate(VI) O 2 + [PtF 6 ] - O 2 + PtF 6 IE = MJ·mol -1 What are the ionization energies of the noble gases? He = 2.37 MJ·mol -1 Ne = 2.08 Ar = 1.52 Kr = 1.35 Xe = 1.17