南郵材料化學(xué)mc20xx-chapter2-a-資料下載頁(yè)
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【正文】 h Characteristics Properties of pound Covalent sharing of pairs of electrons between atoms stronger Saturated and directional； low coordination number. High melting point and Hardness, Good optical Property, nonconductive Hydrogen Coulomb force of H and atoms with high electronegative weak Van der walls Induction between dipoles in atoms weakest Nondirectional and unsaturated, closepacked High melting point, nonconductive 41 Bonds in actual materials Bonds in the practical materials 42 Interaction and bond energy between atoms ※ Potential Energy Well ※ Calculation of bond energy 43 ——curve of relationship between the total potential energy (E) and distance of atoms. E＝ EA＋ ER EA: electrostatic attractive energy A maEr??a—constant。 r—radius m=1 (ion)。 m=6 (molecule) ER: electrostatic repulsive energy R nbEr?AB mnabE E Err? ? ? ? ?n—repulsive index b—constant 1） Potential Energy Well 44 00 rrdEFdr ?? ? ?10nmnbrma????????Bond length r0 —— equalibrium bond distance dEF dr??Potential energy well The deeper the PEW, the packer the bonding of atoms, the more difficult to melt and the higher elastic modulus and lower thermal coefficient of expansion 45 2） calculation of bond energy A R i onsE E E E? ? ? ?Energy for the formation of positive and negative ions Potential energy E0 at the balance site 0 , 0 , 0A R ion sE E E E? ? ? ?46 ： Calculation of bond energy of NaCl 1, 4 9 8 3 5 4 1 4 4 k J/m o lion s Na ClE I E A? ? ? ? ? ?Ion formation energy Attractive energy EA,0 22 0/ ( 4 )AF e r????0 2, 0 0 0/ ( 4 )rAAE F d r e r???? ? ??A maEr??2 0/4ae ????Repulsive energy ER,0 2, 0 0 0/ ( 4 )RE e nr??? 2 2 200 0 0 0 0 019 2 23 112 2 2 10114 4 41 1 ( 10 C) ( 2 10 m ol )1 1428 4 ( 54 10 C / N m ) ( 6 10 m 371 kJ/m olion s ion se e eE E Er nr n r? ? ? ? ? ???????? ??? ? ? ? ? ? ? ??????? ????? ? ???? ? ??? ??? ? ??? ????Bond energy E0 How?
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