材料科學(xué)基礎(chǔ)英文版課件_(8)-預(yù)覽頁
【正文】 ramic materials ? Metallic bonds in metallic materials ? Both primary and secondary bonds in polymeric materials ., in liquid N2, NN NN Primary interatomic bonds (2) 1) Ionic bonds Sodium chloride: NaCl Cl Formation of an ionic bond between a sodium atom and a chlorine atom 2o2A 4 rqF ???rqrFUro2AA 4d ????? ??nR rBU ?Bonding energy: Ubonding = Ui – (UA + UR) Ui =energy of isolated ions RA UUU ??bPrimary interatomic bonds (3) The formation of an ionic bond, viewed in terms of energy Ubonding Primary interatomic bonds (4) 2) Covalent bonds The bond is formed by sharing of electrons between adjacent atoms . Methane (CH4) The formation of covalent bonds in CH4 Primary interatomic bonds (5) Bond energy: Ub = A/rm + B/rn (mn) The formation of a covalent bond, viewed in terms of energy Ubonding Primary interatomic bonds (6) Compound – partially ionic bonding and partially covalent bonding Degree of either bonding type – difference in the electronegativity of ponent atoms For a pound posed of two elements A and B % ionic character = {1 exp[()(XAXB)2]}?100 XA and XB – electronegativities of elements A and B Increasing with increasing electronegativity difference 3) Metallic bonds Dominant interatomic bonding in metals Metal ion cores + free electrons (valence electrons) Primary interatomic bonds (7) Bonding in a metal Secondary bonds (1) ? Much weaker than primary bonds, but important – Links between polymer molecules – solids – Keep water liquid at room temperature
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