第十二章氧族元素 Chapter 12 Oxygen Family Elements
第十二章 氧族元素 Chapter 12 Oxygen Family Elements
Oxygen Sulphur Selenium Se Tellurium Polonium Te Po 也称为成矿元素 (ore-forming element)
Oxygen Sulphur Selenium O S Se Tellurium Polonium Te Po 也称为成矿元素 (ore-forming element)
812-1 Oxygen and its compounds 、 Simple substance 1.除了He、Ne、Ar以外,氧与所有元素化 合,只有与氟化合时,才呈还原性。 2.最常见的氧化数为-2还有+2(OF2) +4[o(02)],+1(02F2)r-1(HO2) 3.氧的单键离解能为142KJmo,而硫 为268K]mol氧分子离解能为494kJ/mol
§12-1 Oxygen and its compounds 一、Simple substance 1. 除了He、Ne、Ar以外，氧与所有元素化 合，只有与氟化合时，才呈还原性。 2. 最常见的氧化数为-2,还有+2 (OF2) , +4[O(O2)] , +1(O2F2) , -1(H2O2) 3. 氧的单键离解能为142KJ·mol-1，而硫 为268KJ·mol-1。氧分子离解能为494 kJ/mol
率 22 r2p.元2 ￥y M 2p I 2p t协 r2px t2p G2p
解释 (1)氧的原子半径小,孤对电子对之间有较大 的排斥作用 (2)氧原子没有空的d轨道,不能形成d-pπ键, 所以OO单键较弱 对于02分子而言,除了σ键外,还有二个 电子键,所以O2-20比较困难,要求加热到 2000°C,要求紫外光照射 氧元素在地球上的丰度最高,达58%(以mo计
解释: (1) 氧的原子半径小，孤对电子对之间有较大 的排斥作用 (2) 氧原子没有空的d轨道，不能形成d—p键， 所以O—O单键较弱 对于O2分子而言，除了σ键外，还有二个三 电子π键，所以O2—2O比较困难，要求加热到 2000oC ，要求紫外光照射 氧元素在地球上的丰度最高，达58%(以mol计)
二、 Compounds: 1.[-2]0S 最重要的化合物是水。 水分子轨道能级图如右图, MOm 它解释了水存在四个第一电离吾4份"济5 势。 2H 分子轨道表示为: (os)2(0z2Oxnon)2(nyon )2 2s H-o
二、Compounds: 1. [-2]O.S. 最重要的化合物是水。 水分子轨道能级图如右图， 它解释了水存在四个第一电离 势。 分子轨道表示为： (σS) 2(σZ) 2(σX non) 2(πY non) 2
C2X 2p (-1)X x 2 (+1)x2py
The 1s, 2s and 2p, orbitals of oxygen are symmetric (i.e, unchanged)with respect to all three symmetry operations. They are given the symmetry classification a The 2px orbital, since it possesses a node in the o2 plane(and hence is of different sign on each side of the plane) changes sign when reflected through the o2 plane or when rotated by 180 about the C? axis. It is classified as a b2 orbital. The 2p orbital is antisymmetric with respect to the rotation operator and to a reflection through the o, plane. It is labelled b, The hydrogen 1 s orbitals when considered separately are neither unchanged nor changed in sign by the rotation operator or by a reflection through the o, plane Instead both these operations interchange these orbitals. the hydrogen orbitals are said to be symmetrically equivalent and when considered individually they do not reflect the symmetry properties of the molecule. However, the two linear combinations (1s,+ 1s2) and (1s,-1s2) do behave in the required manner. The former is symmetric under all three operations and is of a, symmetry while the latter is antisymmetric with respect to the rotation operator and to a reflection through the plane o, and is of b2 symmetry The molecular orbitals in the water molecule are classified as a b, or b orbitals as determined by their symmetry properties. This labelling of the orbitals is analogous to the use of the o-I and g-u classification in linear molecules. In addition to the symmetry properties of the atomic orbitals we must consider their relative energies to determine which orbitals will overlap significantly and form delocalized molecular orbitals
The 1s, 2s and 2pz orbitals of oxygen are symmetric (i.e., unchanged) with respect to all three symmetry operations. They are given the symmetry classification a1 . The 2px orbital, since it possesses a node in the s2 plane (and hence is of different sign on each side of the plane) changes sign when reflected through the s2 plane or when rotated by 180° about the C2 axis. It is classified as a b2 orbital. The 2py orbital is antisymmetric with respect to the rotation operator and to a reflection through the s1 plane. It is labelled b1 . The hydrogen 1s orbitals when considered separately are neither unchanged nor changed in sign by the rotation operator or by a reflection through the s2 plane. Instead both these operations interchange these orbitals. The hydrogen orbitals are said to be symmetrically equivalent and when considered individually they do not reflect the symmetry properties of the molecule. However, the two linear combinations (1s1 + 1s2 ) and (1s1 - 1s2 ) do behave in the required manner. The former is symmetric under all three operations and is of a1 symmetry while the latter is antisymmetric with respect to the rotation operator and to a reflection through the plane s2 and is of b2 symmetry. The molecular orbitals in the water molecule are classified as a1 , b1 or b2 orbitals, as determined by their symmetry properties. This labelling of the orbitals is analogous to the use of the s- and g-u classification in linear molecules. In addition to the symmetry properties of the atomic orbitals we must consider their relative energies to determine which orbitals will overlap significantly and form delocalized molecular orbitals
The molecular orbitals in the water molecule are classified as a, b or b orbitals as determined by their symmetry properties. This labelling of the orbitals is analogous to the use of the o-T and g-u classification in linear molecules. In addition to the symmetry properties of the atomic orbitals we must consider their relative energies to determine which orbitals will overlap significantly and form delocalized molecular orbitals The 1s atomic orbital on oxygen possesses a much lower energy than any of the other orbitals of a, symmetry and should not interact significantly with them. The molecular orbital of lowest energy in H2O should therefore correspond to an inner shell 1s atomic like orbital centred on the oxygen. This is the first orbital of a, symmetry and it is labelled la,. Reference to the forms of the charge density contours for the la, molecular orbital substantiates the above remarks regarding the properties of this orbital Notice that the orbital energy of the la, molecular orbital is very similar to that for the 1s atomic orbital on oXygen. The 1a, orbital in H2o is, therefore, similar to the lo inner shell molecular orbitals of the diatomic hydrides The atomic orbital of next lowest energy in this system is the 2s orbital of a, symmetry on oxygen. We might anticipate that the extent to which this orbital will overlap with the (1s,+ 1s,)combination of orbitals on the hydrogen atoms to form the 2a, molecular orbital will be intermediate between that found for the 2o molecular orbitals in the diatomic hydrides Ch and H. the 2o orbital in Ch results from a strong mixing of the 2s orbital on carbon and the hydrogen 1 s orbital In Hf the participation of the hydrogen orbital in the 2o orbital is greatly reduced, a result of the lower energy of the 2s atomic orbital on fluorine as compared to that of the 2s orbital on carbon
The molecular orbitals in the water molecule are classified as a1 , b1 or b2 orbitals, as determined by their symmetry properties. This labelling of the orbitals is analogous to the use of the s- and g-u classification in linear molecules. In addition to the symmetry properties of the atomic orbitals we must consider their relative energies to determine which orbitals will overlap significantly and form delocalized molecular orbitals. The 1s atomic orbital on oxygen possesses a much lower energy than any of the other orbitals of a1 symmetry and should not interact significantly with them. The molecular orbital of lowest energy in H2O should therefore correspond to an inner shell 1s atomiclike orbital centred on the oxygen. This is the first orbital of a1 symmetry and it is labelled la1 . Reference to the forms of the charge density contours for the la, molecular orbital substantiates the above remarks regarding the properties of this orbital. Notice that the orbital energy of the la1 molecular orbital is very similar to that for the 1s atomic orbital on oxygen. The 1a1 orbital in H2O is, therefore, similar to the ls inner shell molecular orbitals of the diatomic hydrides. The atomic orbital of next lowest energy in this system is the 2s orbital of a1 symmetry on oxygen. We might anticipate that the extent to which this orbital will overlap with the (1s1 + 1s2 ) combination of orbitals on the hydrogen atoms to form the 2a1 molecular orbital will be intermediate between that found for the 2s molecular orbitals in the diatomic hydrides CH and HF. The 2s orbital in CH results from a strong mixing of the 2s orbital on carbon and the hydrogen 1s orbital. In HF the participation of the hydrogen orbital in the 2s orbital is greatly reduced, a result of the lower energy of the 2s atomic orbital on fluorine as compared to that of the 2s orbital on carbon
Aside from the presence of the second proton, the general form and nodal structure of the 2a, density distribution in the water molecule is remarkably similar to the 2o distributions in CH and HF, and particularly to the latter. The charge density accumulated on the bonded side of the oxygen nucleus in the 2a, orbital is localized near this nucleus as the corresponding charge increase in the 2o orbital of HF is localized near the fluorine. The charge density of the 2a, molecular orbital accumulated in the region between the three nuclei will exert a force drawing all three nuclei together. The 2a, orbital is a binding orbital Although the three 2p atomic orbitals are degenerate in the oxygen atom the presence of the two protons results in each 2p orbital experiencing a different potential field in the water molecule. the nonequivalence of the 2 p orbitals in the water molecule is evidenced by all three possessing different symmetry properties The three 2p orbitals will interact to different extents with the protons and their energies will differ The 2px orbital interacts most strongly with the protons and forms an orbital of b2 symmetry by overlapping with the(1s,-1s2) combination of 1 s orbitals on the hydrogens. The charge density contours for the Ib2 orbital indicate that this simple LCAO description accounts for the principal features of this molecular orbital. The lb2 orbital concentrates charge density along each O-H bond axis and draws the nuclei together. The charge density of the 1b2 orbital binds all three nuclei. In terms of the forces exerted on the nuclei the 2a, and Ib2 molecular orbitals are about equally effective in binding the protons in the water molecule
Aside from the presence of the second proton, the general form and nodal structure of the 2a1 density distribution in the water molecule is remarkably similar to the 2s distributions in CH and HF, and particularly to the latter. The charge density accumulated on the bonded side of the oxygen nucleus in the 2a1 orbital is localized near this nucleus as the corresponding charge increase in the 2s orbital of HF is localized near the fluorine. The charge density of the 2a1 molecular orbital accumulated in the region between the three nuclei will exert a force drawing all three nuclei together. The 2a1 orbital is a binding orbital. Although the three 2p atomic orbitals are degenerate in the oxygen atom the presence of the two protons results in each 2p orbital experiencing a different potential field in the water molecule. The nonequivalence of the 2p orbitals in the water molecule is evidenced by all three possessing different symmetry properties. The three 2p orbitals will interact to different extents with the protons and their energies will differ. The 2px orbital interacts most strongly with the protons and forms an orbital of b2 symmetry by overlapping with the (1s1 - 1s2 ) combination of 1s orbitals on the hydrogens. The charge density contours for the lb2 orbital indicate that this simple LCAO description accounts for the principal features of this molecular orbital. The lb2 orbital concentrates charge density along each O-H bond axis and draws the nuclei together. The charge density of the 1b2 orbital binds all three nuclei. In terms of the forces exerted on the nuclei the 2a1 and lb2 molecular orbitals are about equally effective in binding the protons in the water molecule
