IV. Electronic Structure and Chemical Bonding Qualitative Bonding Notions J.K. Burdett, Chemical Bonding in Solids Distance Volume The Chemical Bond in Solids 1 Characteristics Dissociation Energy Bond Distance Vibrational Force Constant
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IV. Electronic Structure and Chemical Bonding
Qualitative Bonding Notions J.K. Burdett, Chemical Bonding in Solids Distance / Volume The Chemical Bond
in
Solids 1 Characteristics
Dissociation Energy
Bond Distance
Vibrational Force Constant Reference State Attractive Terms Repulsive Terms A–B A(g) + B(g) A+(g) + B–(g) I A Pauli-Exclusion
Nuclear-Nuclear Electrostatic
Orbital Overlap Distance Energy The Chemical Bond<br>
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2 Experimental Measurement and Assessments
Electrical Conductivity – (thermal or optical) band gaps
Magnetic Susceptibility – localized or itinerant; para- or diamagnetic
Heat Capacity – specific heat due to conduction electrons and lattice
Cohesive Energy – energy required to convert M(s) to M(g)
Spectroscopy – valence electronic density of states; core state binding energies
Phase Changes – structure changes with temperature or pressure variations IV. Electronic Structure and Chemical Bonding
Qualitative Bonding Notions J.K. Burdett, Chemical Bonding in Solids<br>
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3 Average “Electronegativity” “Electronegativity”
Difference Ionic
Dense Packed CsF Cs F Al Si P Cl S Na Mg GaAs Metallic
Dense Packed Covalent
Molecular LiAl InBr L.C. Allen, JACS, 1989, 111, 9003; 1992, 114, 1510
L.C. Allen et al., JACS, 2000, 122, 2780 and 5132 Decreasing
Electron Transfer Decreasing
Electron Delocalization Decreasing
Structural Anisotropy IV. Electronic Structure and Chemical Bonding
Qualitative Bonding Notions: van Arkel-Ketelaar Triangle (Basics) Pauling: “The power of an atom in a compound to attract e–s to itself.”<br>
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4 Average “Electronegativity” “Electronegativity”
Difference Ionic
Dense Packed CsF Cs F Al Si P Cl S Na Mg GaAs Metallic
Dense Packed Covalent
Molecular LiAl InBr Electrical Conductors
Paramagnetic or itinerant magnetism
Soft – malleable, ductile
Reflective Electrical Insulators
Diamagnetic or localized magnetism
Volatile (low boiling points)
Transparent Electrical insulators; Conducting liquids
Diamagnetic or localized magnetism
Brittle
Transparent IV. Electronic Structure and Chemical Bonding
Qualitative Bonding Notions: van Arkel-Ketelaar Triangle (Physical Properties)<br>
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5 Average “Electronegativity” “Electronegativity”
Difference Ionic
Dense Packed CsF Cs F Al Si P Cl S Na Mg GaAs Metallic
Dense Packed Covalent
Molecular LiAl InBr Electrical Semiconductors
Diamagnetic
“Hard” – Brittle
Transparent Elect. Semiconductors or Semimetals
Diamagnetic
“Hard” – Brittle
Opaque ↔ Transparent Elect. Semiconductors or Semimetals
Diamagnetic
“Hard” – Brittle
Opaque – Nonreflective M(g) M(s) X(g) X(s) M(g) + X(g) MX(s) ?? ?? ?? How can we understand the different types of chemical bonding in solids? IV. Electronic Structure and Chemical Bonding
Qualitative Bonding Notions: van Arkel-Ketelaar Triangle<br>
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6 IV. Electronic Structure and Chemical Bonding
Qualitative Bonding Notions: Ionic Solids NaCl Na 3s Cl 3p Cl– 3p Na+ 3s Na(g) + Cl(g) Cl– 3p Na+ 3s INa–ACl = 1.52 eV “Valence Band” “Conduction Band” MAX 400 nm Eg > 3 eV P.K. de Boer, etc., Phys. Lett. A, 1999, 256, 227 Cl 4s Na+(g) + Cl–(g) Energy Madelung Potential Polarization NaCl(s)<br>
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7 IV. Electronic Structure and Chemical Bonding
Qualitative Bonding Notions: Covalent Solids Si (Diamond) MAX > 400 nm Ep Es 12-14 eV 18-19 eV Eg < 3 eV sp3 Hybrids b1 b2 2b2 4b1 4b1 Orthogonal in space not in energy PES: SiH4 SiH4+ t2 a1 Semiconducting Energy “Valence Band” “Conduction Band” Si(s) Si(g) DHvap = 4.72 eV DHvap 4D(Si-Si) / 2 = 4.72 eV D(Si-Si) / 2 = 2.36 eV 2.34 eV Eg 2β2 – 4β1<br>
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8 IV. Electronic Structure and Chemical Bonding
Qualitative Bonding Notions: Metallic Solids Ep Es Energy Fermi
Level “Conduction Band” Na (BCC) Ep Es Energy Ed Nb (BCC; d-metal) DE << kT Fermi
Level d Band<br>
