Long Answer TypeWhich of the following combinations of orbtials are allowed in LCAO method (considering z-axis to be molecular axis) and sketch the shapes of molecular orbitals formed by their addition and subtraction:
(i) s and pz
(ii) px and px
(iii) pz and py
(iv) s and px.
What informations are conveyed from the electronic configuration of the molecule?
The information is conveyed from the electronic configuration.
(a) From the electronic configuration, it is possible to find out the number of electrons in bonding molecular orbitals (Nb) and a number of electrons in anti-bonding orbitals (Na).
(i) The molecule is stable if Nb > Na.
(ii) The molecule is unstable if Nb < Na.
(iii) The molecule is unstable if Nb = Na.
It may be noted that even if the number of electrons in bonding M.O. and the number of electrons in anti-bonding M.O. are equal, the atoms do not combine to form a molecule. This is because of the fact that the destabilising effect of anti– bonding electrons is slightly more than the stabilising effect of bonding electrons.
(b) To predict the magnetic behaviour of molecules i.e. if all the electrons in a molecule are paired, the substance is diamagnetic and in case there are unpaired electrons in a molecule, the substance is paramagnetic.
Short Answer TypeGive the number of electrons which occupy the bonding molecular orbital in H2+ H2 and He2.
What do you understand by bond order? How is it related with bond length and bond energy? Explain on the basis of bond order that He2 molecule does not exist.
Long Answer TypeUsing LCAO method for the formation of molecular orbitals in case of homonuclear diatomic hydrogen molecule.
Draw the molecular orbital diagram for:
(i) Be2
(ii) B2 and predict bond order and magnetic properties.
Short Answer Type
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