MO diagram for homonuclear diatomic molecules Li 2

MO diagram for homonuclear diatomic molecules Li 2 through N 2 MO diagram for homonuclear diatomic molecules O 2 and F 2

N 2 Lewis diagram : N N: each atom supplies 5 electrons; a total of 10 electrons must be assigned N 2: s 2 s 2 s*2 s 2 p 2 p 4 s 2 p 2 Bond order for N 2 = 0. 5 (8 - 2) = 3

O 2 Lewis model Molecular Orbital Theory O 2: s 2 s 2 s*2 s 2 s 2 p 2 p 2 p 4 p*2 p 1 Unpaired electrons - paramagnetic Bond order = 2 Agrees with Lewis diagram

Heteronuclear diatomics - electrons are unequally shared by the two atoms due to electronegativity differences. y = c A y. A + c B y. B Where c. A and c. B are coefficients which indicate the contribution of each AO in the MO In a homonuclear molecule: c. A = c. B = 1

MO energy-level diagram for a AB type molecule. A is more electronegative than B Energy levels of the more electronegative element is lower than the less electronegative element s: higher contribution from A 2 s s*: higher contribution from B 2 s

Lowest unoccupied MO (LUMO) Highest occupied MO (HOMO) CO - ten valence electrons CO: s 2 s 2 s*2 s 2 p 2 p 4 s 2 p 2 Bond order = 0. 5 (8 - 2) = 3

Polyatomics - same principles as diatomics except that the MOs spread all over the atoms in the molecule An electron pair helps to bind the whole molecule, not just a pair of atoms. H 2 O: six atomic orbitals (one O 2 s, three O 2 p, and two H 1 s) These six orbitals are used to build six molecular orbitals in which the degree of net bonding characters is related to the number of internuclear nodes.

Molecular Orbitals of H 2 O

http: //www. whfreeman. com/chemicalprinciples/con_index. ht m? 03 http: //www. shef. ac. uk/chemistry/orbitron/

Spectroscopy: interaction of light with matter Average Bond energies (k. J/mol) C-H: 413 C=C: 610 H-H: 436 C C: 835 H-F: 565