Molecular Orbital Diagrams (Page 2 of 2) in pdf

Molecular Orbital Diagrams Page 2

Figure 3: The H

molecular orbital diagram.

Making MO diagrams

Making MO diagrams requires knowing two diﬀerent things: the ﬂow diagram by which MO diagrams

are generated and the rules by which the ﬂow-chart is processed.

2. The ﬂow chart: Please carry out the steps below to generate the MO diagram for H

(a) Place the two atomic orbital (AO) energy diagrams on the two sides of the sheet of paper.

(b) Place the correct electron ﬁllings for the two AO diagrams, in this case one electron for each AO.

antibonding. They are indicated by horizontal lines in an orbital energy diagram at the middle

of the page.

(d) Draw the MOs which correspond with the new horizontal lines.

(e) Follow the Aufbau principle and ﬁll the middle horizontal lines with the correct number of elec-

trons.

3. The rules There are three rules for making MO diagrams:

(a) In a minimal basis set MO diagram, the number of MOs equals the number of AOs.

(b) When two orbitals combine, they combine to make two new orbitals. The original orbitals combine

to make the lowest and highest energy combinations possible.

apart in energy. When two orbitals of diﬀerent energy combine, the resultant low energy combi-

nation resembles more the initially lower energy orbital; the resultant high energy combination

resembles more the initially high energy orbital. Two orbitals of equal initial energy combine to

make two new orbitals with equal contributions from the two starting orbitals equally.

4. Please examine the H

MO diagram you have just made with the H

drum analog which you previously

analyzed. Are the two diagrams in agreement with one another? If so, how so? If not, why not?

Molecular Orbital Diagrams Page 2