1. Rotation about single and multiple bonds
butene rotation

2. Molecular Orbital Theory
Molecular orbital theory postulates that the combination of atomic orbitals on different atoms forms molecular orbitals (MOs), so that electrons in them belong to the molecule as a whole.
Valence Bond theory postulated that bonds were formed (sharing of electrons) by the overlap of pure atomic or hybrid orbitals of different atoms.
Valence bond theory fails to account for the fact that O2 is paramagnetic .. ..
O O .. .. .. ..

3. Bonding and Anti-bonding Orbitals
Molecular Orbital Diagram
1s *
 (Sigma star)
1s
 (Sigma)
Atomic
Orbital
Atomic
Orbital
Molecular
Orbitals

4. Molecular
Orbital
Diagram
for H2
(#e- in bonding orbitals) - (#e- in anti-bonding orbitals) 2
Bond Order =
Bond Order for H2 = (2-0)/2 = 1

5. Molecular
Orbital
Diagram
for H2
BO=1
Molecular
Orbital
Diagram
for He2
BO (He2)=(2-2)/2=0

6.  anti-bonding
Molecular Orbital
Atomic P Orbitals
 bonding
Molecular Orbital
 bonding
Molecular Orbital
 bonding
Molecular Orbital
Atomic P Orbitals

7. This information is in Table 9-1 of your book
Go to Saunders 10-11
This information is in Table 9-1 of your book