Discussion  Fr 09.12.2005 at 12:15,  HR 30.1

Home work 6            MOs: heteronuclear molecules

Exercise 1:     Electron configurations of diatomic molecules  

a) What are the MO electron configurations of CH, NH, and OH in the ground state and in the first excited states?

b) Do these molecules have a dipole moment? If yes, order of the dipole moments according to their magnitude (take into account also the dipole moments of HF and LiH discussed at the lecture). Hint: first consider the electron structure of the atoms and their ionization potentials

Exercise 2:    Construction of a sp² hybrid

The first sp² hybrid is given by

                            h₁ = - ¹/_Ö3(2s) + Ö(²/₃) (2p_x)

Construct a second hybrid orbital of the form

                           h₂ = - ¹/_Ö3 (2s)  + c₁ (2p_x)  + c₂ (2p_y)

Find the coefficients c₁ and c₂ using the normalization and orthogonality of the orbital h₂ with respect to h₁ .

Exercise 3:   p orbitals

a) Qualitatively consider ethyne C₂H₂ and  ethane C₂H₆  molecules using the Hückel approximation. Which hybrid orbitals are appropriate for forming the molecular skeleton? Explain which orbitals are involved in formation of the triple (ethyne) and single (ethane) bonds between the carbon atoms.  

b) Using you knowledge about bonding in ethane (C₂H₆) and ethene (C₂H₄) molecules try to explain why rotation of the two parts of the molecule around C-C bond is not possible in C₂H₄, but is easily possible in C₂H₆. 

 

 

 

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