Orbital theory

Question 1

What does photoelectron spectroscopy show?

Answer 1

Electrons have distinct energies (ionisation energy)

Question 2

What are the four quantum numbers of an electron?

Answer 2

1. Principal (n): determines energy and specifies shell
2. Angular momentum/azimuthal (l): specifies orbital angular momentum (spdf)
3. Magnetic (me): determines orientation of orbital (px, py…)
4. Spin angular momentum: +/- 1/2 for electron

Exclusion principle: two electrons cannot have same quantum numbers

Question 3

Wavefunction

Answer 3

A function describing the properties of an electron

Question 4

Born interpretation

Answer 4

Probability proportional to modulus of wavefunction squared

Question 5

Radial distribution function

Answer 5

Probability of finding e in a shell (thickness dr) at certain distance from nucleus

Question 6

Shape of 1s orbitals

Answer 6

No radial or angular nodes

Question 7

Shape of 2s orbital

Answer 7

One radial node, no angular nodes

Question 8

Shape of 2p orbital

Answer 8

One angular node, no radial nodes. Node at 0.

Question 9

Shape of 3s orbital

Answer 9

Two radial nodes. No angular nodes.

Question 10

Shape of 3p orbital

Answer 10

One radial, one angular node

Question 11

Shape of 3d orbital

Answer 11

No radial nodes, 2 angular nodes.
3dz2 = nodal cone (54.7, 125.3deg)

Question 12

Nodes

Answer 12

Number of nodes = n-1
Angular nodes = l

s (l=0) p (l=1) d (l=2) f (l=3)

Question 13

Why is MO lower in energy than AOs?

Answer 13

• Lower PE in internuclear region
• Electron moves over larger area so has lower KE

Question 14

Symmetry of MOs

Answer 14

Sign changes when rotating around axis: pi (else sigma)

Sign changes through centre of inversion: u (else g)

Question 15

Factors determining how well AOs combine

Answer 15

1. Symmetry
2. Energy difference (smaller means stronger interaction)
3. Orbital size (larger orbitals means stronger interaction)

Question 16

Factors determining how well AOs combine

Answer 16

1. Symmetry
2. Energy difference (smaller means stronger interaction)
3. Orbital size (larger orbitals means stronger interaction)

Question 17

Number of nuclear energy levels

Number of ways NMR signal split

Answer 17

2I+1 (where I is spin of nucleus)

Question 18

Contribution to MOs in heteronuclear diatomics

Answer 18

• Unequal contribution gives ionic character
• Higher energy AO contributes more to antibonding, lower AO contributes more to bonding

Question 19

What is sp mixing?

Answer 19

• In elements up to N, 2s sigma antibonding orbital is high enough to interact with 2p sigma bonding orbital
• Makes 2s less antibonding, and 2p less bonding
• Also affects energies of 2s bonding/2p antibonding to a lesser extent

Question 20

Conjugated systems

Answer 20

For many p orbitals in a line, draw sine wave diagrams. AOs = MOs. Then fill from bottom.

Question 21

Hybridisation for each geometry

Answer 21

• linear - sp
• trigonal planar - sp2
• tetrahedral - sp3
• square planar - sp2d or p2d2
• trigonal bipyramidal - sp3d or spd3
• octahedral sp3d2