Mix and Match the orbitals! In class activity Mix and Match the orbitals!

Large sized ligand group orbitals (LGO) and the valence orbitals of the metal were separately printed out on A4 sheets. 1 per A4 sheet. The printed orbitals were folded put into a basket. 17 sheets (8 ligand group orbitals and 9 metal orbitals) are available. Each student was asked to pick one sheet. (If there are more than 17 students, students can be asked to pair up.) If less no. of students are there a few pairs can be used for the demonstration and not distributed to the class for matching! Or some students could do match more than one!

The coordinate system to be used was indicated. The metal orbitals were not shaded. So the students marked + (plus) and – (minus) on the lobes. One LGO was held up and it was matched with metal orbitals till the correct match was identified. The molecular orbital was identified as σ, π, or δ, type interactions. The correct lobe was then shaded to match the orientation of the ligand group orbital. It the sheet is semitransparent, it can be held against the light to see the match!

The core activity took about 15 minutes for my 12 students. Five minutes to explain the activity and to give out the sheets to 12 students. The axis were also indicated. Some students took extra orbitals. Some interactions (σ ) were quickly discovered. But some took time; especially the δ type interactions. The matched orbitals were then shown to the whole class by those who had matched it. This took another 5 minutes. Doubts were cleared. This helped the students to understand how symmetry is important. The energy level diagram was appreciated much better after the exercise.

To make it easy, the metal orbitals could be shaded appropriately. The students can be asked to draw the ligand group orbitals which were not included in the matching. The ligand group orbitals of bis cyclopentadienyl units could be given to illustrate formation of ferrocene molecular orbitals.

The “yz” plane is the plane of the paper The benzene rings are on the “xy” plane

Metal orbitals

“a” and “eu”orbitals of (C6H6)2

egorbitals of (C6H6)2

Key to the combinations LGO Metal a1g s e1u py dz2 px a2u pz e1g d xz dyz e2g d x2- y2 dxy