物理课件26-2.ppt

26.3 Ionic bonding Na(1s2 2s2 2p6 3s) 5.14eV Na+ Cl(1s2 2s2 2p6 3s2 3p5) + e ? Cl – + 3.61eV electron affinity Free Na Cl as E = 0 S = 0 d Two ions come closer and release energy further. The closer, the more stable? Collapse? Na+(1s2 2s2 2p6) Cl– (1s2 2s2 2p6 3s2 3p6) If collapse , p-orbitals will overlap! Quantum effect dominates. the equilibrium separation is 0.236 nm energy is –4.26 eV. The answer is no! Can completed p-orbitals overlap each other? Can other electrons enter a completed shell? Ionic or covalent? Generally homonuclear diatomic molecules are formed through covalent bonds. A finite electric dipole is indication of ionic bond. there is no “pure” covalent bond. While in heteronuclear molecules In NaCl the separation is 0.236nm But the measured electric dipole moment is 3.00 ×10 – 29C·m percent ionicity is 3.00/3.78 = 79.4% Intermolecular force: chemical bonds (200 ~ 500 kJ·mol–1) hydrogen bonds (5 ~ 50 kJ·mol–1) induced dipole force (~ r –7) dipole-dipole interaction (~ r –3) polypeptide chains H2O Amino acid residue 26.4 Molecule vibration and rotation The vibration energy levels The rotation energy levels *26.5 Biological macromolecule proteins and nucleic acids Proteins in nature are built of twenty kinds of amino acids side chain 羧基 氨基 amino acids(氨基酸) 11. Alanine(Ala) 丙氨酸 12. Arginine(Arg) 精氨酸 13. Cysteine(Cys) 半胱氨酸 14. Glutamic acid(Glu) 谷氨酸 15. Aspartic acid(Asp) 天门冬氨酸 16. Threonine(Thr) 苏氨酸 17. Serine(Ser) 丝氨酸 18. Glycine(Gly) 甘氨酸 19. Asparagine(Asn) 天门冬酰胺 20. Glutamine(Gln) 谷氨酰胺 1. Tryptophan (Trp) 色氨酸 2. Isoleucine (Ile) 异亮氨酸 3. Tyrosine (Tyr) 酪氨酸 4. Phenylalanine (Phe)苯丙氨酸 5. Proline (Pro) 脯氨酸 6. Leucine (Leu) 亮氨酸 7. Valine (Val) 缬氨酸 8. Lysine (Lys) 赖氨酸 9. Histidine (His)