化学键与分子结构.ppt

第八章 分子结构与晶体结构 (1) Questions? Why is calcium phosphate so rigid that nature has adopted it for the formation of bones? Can we make better bones? (强离子键) Why is it so difficult to make compounds from the nitrogen in air? Can we find an easy way? (强共价键) How can we explain the ability of hemoglobin to form a loosely bonded compound with oxygen, transfer it to another part of the body, and then release it in response to a metabolic need? (配位键) 序言： 原子怎样结合成为分子？ － 化学键 离子键 共价键 金属键 分子的形状？ － 分子构型 价电子对互斥理论 分子怎样组成物质材料？－分子间作用力 固体材料的结构？ －晶体结构 －无定型结构 1、离子键 (Ionic Bonds) Lewis结构式和八隅体规则 离子键及其特点 离子键强度与晶格能 离子化合物的性质 为什么惰性气体稳定？ ns2np6 八电子层结构 离子键及其特点： 离子键强度与晶格能： 定义：晶格能表示相互远离的气态正离子和负离子结合成 1 mol 离子晶体时所释放的能量，或1 mol 离子晶体解离成自由气态离子时所吸收的能量。（A measure of the attraction between ions is lattice enthalpy, the enthalpy change per mol of formula units when a solid is broken up to a gas of widely separated ions.） （取其绝对值）如： Ca2+ (g) + 2Cl- (g) CaCl2 (s) – ?H = U = 2260.kJ/mol 离子键强度与晶格能： Born-Lande 公式 U = -Ve ∝ Z1Z2/r 其中： Ve 为正负离子间吸引力和排斥力达平衡时，体系的位能；Z1、Z2 分别为正负离子的电荷数； r为正负离子间距。 the closer the center of charge and the greater the charges, the stronger will be the interaction。 Born-Haber 循环计算U （自学，第11章，p区元素） 离子化合物的性质 (The Properties of Ionic Compounds) 高熔点 High melting points 高沸点 High boiling points 易脆性 Brittleness 溶解性 Some are soluble, some not. [例] Ca3(PO4)2：骨头的主要成分 The doubly charged small Ca2+ ions, and the triply charged PO43- ions attract one another very strongly and clamp together to form a rigid, insoluble solid. (not completely insoluble, osteoporosis，骨质疏松症) 2、共价键 (Covalent Bonds) 从原子到分子 (from atoms to molecules) 八隅率与Lewis结构 (The octet rule and Lewis structure) 双原子分子 多原子分子 共振杂化 形式电荷 例外 广义八隅率 (Expended valence shells) Lewis 酸碱 (Lewis acids and bases) 八隅率与Lewis结构 The octet rule and Lewis structure The octet rule: In covalent bond formation, atoms go as far as possible toward completing their octet by sharing electron pairs. The valence of an element