Lecture 4 Aufbau, Pauli and Hund

Question 1

Can you solve the Schrodinger equation for atoms with >1 electron? Why?

Answer 1

No, because the electrons interfere with each other

Question 2

In an atom with >1 electron, what determines energies of orbitals?

Answer 2

n and l

Question 3

In an atom with <1 electron, what determines energies of obitals?

Answer 3

n only. ml if magnetic field

Question 4

On this image, what are the orbitals (s,p,d,f?)

If 0pm is the nucleus, which is the most stable? Why?

Answer 4

Top is s, then, p then d. Although the main bulk of d the electron is nearer. In s orbitals there is a probablitily that the electron will spend some time very close to the nucleus making it the most stable

Question 5

What does Zeff mean? What does Z stand for?

What does Slater’s rules give?

Answer 5

Zeff means the effective nuclear charge. Z is nuclear charge.

Zeff = Z-S

S is shielding coefficient

Slater’s rules give estimate of effective nuclear charge

Question 6

Name the 4 Slater’s rules

Answer 6

1. S orbitals to the right of the electron being conidered do not contribute
2. S orbital in same group as one considered contribute 0.35 except 1s which contributes .030
3. If you are condering a ns or np orbital, electrons in next shell (n-1) contribute 0.85 and lower than that is 1
4. If you are condsidering a nd or nf all the electrons below contribute 1

Question 7

Calculate Zeff for Iron, electron 3s

Answer 7

(1s²) (2s² 2p⁶) (3s² 3p⁶) (3d⁶) (4s² 4p⁰) Atomic Number = 26 = Z

S= (7x0.35) + (8x0.85) + (2x1.00) = 11.25

Zeff = Z - S = 26 - 11.25 = 14.75

Question 8

What is Ms and what does it detirmine? What are it’s allowed values?

Answer 8

Atomic Spin Number, detirmines how many electrons we can fit in each orbital

+ or - 1/2

Question 9

What is Paulis Exclusion Principle?

How does it explain max electrons in any orbital?

Answer 9

No two electrons in any system can have the same quantum numbers

In any orbital electrons by definition have same n, l, ml so ms has to be different. It can only have 2 values (+ or - 1/2) so only 2 electrons in any orbital with opposed spins

Question 10

Which is correct and what does Hund’s Rule say?

Answer 10

C, the most stable electronic state is the one with the most parallel spins so C

Question 11

What are the trends of Atomic Radius across Group 1?

Answer 11

Steady increase

Question 12

What are the trends across group 13?

Answer 12

General increase as layers are added but in the appearance of a d or f block there is a contraction because they are bad at shielding nucleus pull unlike s and p orbitals because of their shape

Question 13

What happens to atomic radius across a period?

Answer 13

More electrons but not new layer so contracts so gets smaller

Question 14

What has higher ionisation energy, H or Li

Answer 14

H is 1s¹ and Li is 1s¹2s¹so H has higher ionsation, hard to get rid of that electron close to nucleus whereas with Li then it has complete 1s¹ orbital