InorganicChemistry英文PPT (43)冷热源工程.ppt

Chapter 8 Molecular structures§8.1 Valence bond theory§8.4 Key parameters §8.3 Molecular orbital theory§8.2 Valence layer electron pair repulsion theory :C O:One σ bond Two π bondsThe electronic structures are referred as Lewis structuresExamples of violation of octet rule: BF3，PCl5，SF6, etc 2. Modern valence bond theory1. Key points: Unpaired electrons with opposite spins are paired to form bondsMaximum overlap of atomic orbitals for pairing bondingAtomic orbitals overlap with the same sign to form a bond, but opposite signs overlap cannot. (1) the similar energy.3. Characteristics of covalent bond(1) Saturation: when an atom has several unpaired electrons, correspondingly, it can pair with several electrons with opposite spin to form a bond.(2) Directionality: the more valence electron orbitals overlap, the more stable the covalent bond is. 2.The principle of overlapping(2) maximum overlap principle.(3) symmetry matching. The essence of covalent bond is that atomic orbitals overlap, and the probability density of electrons between nuclei is large, which attracts nuclei to form bonds. The electron spin patterns of the two hydrogen atoms are opposite, close to each other and overlap, forming a region of high electron probability density between nuclei. The energy of the system decreases and hydrogen molecules are formed. σ bond, π bond and coordination bondσ Bond: atomic orbitals overlap in a head-on-head manner along the alignment of two nuclei.Schematic illustrations of σ bonds-spx-spx-px8.1.2 types of covalent bondsOverlap of atomic orbitalsProfiles of electron clouds π Bond: atomic orbitals overlap side by side along with the direction of the two nuclear lines.Schematic illustrations of π bondOverlap of atomic orbitalsProfiles of electron clouds +++——+——++——ππOne σ bond, two π bonds:The σ bond is formed by 2px-2px orbitals;The π bonds are formed by 2py-2py; 2pz-2pz orbitals.The direction of p orbital depends on the perpendic