Home work Physical and Theoretical Chemistry IV

- Molecular Spectroscopy -

Discussion  Fr 03.12.2004 at 10:30,  PK11-2



 
Home work 5            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) (2pz)
Construct a second hybrid orbital of the form
h2  =  1/Ö3 (2s)  + c1 (2pz)  + c2 (2px)
which is normalized and orthogonal 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