L5/6 Electronic structure

Question 1

What is quantum theory?

Answer 1

= theoretical basis of modern physics that explains the nature and behaviours of matter and energy on the atomic and subatomic level
Explains:
- the spectra of light emitted by atoms
- that e- in atoms are stable & stay in their orbitals
- wave-particle duality = e- can behave as waves OR particles

Question 2

What are energy levels?

Answer 2

= stable energy levels contain e- in the atom

• the absorption of energy (a photon of light) excites the e- causing them to jump to a higher energy level
• the e- jumping down emits a photon of light

*measuring the energy of the photon allows the energy difference between the energy levels to be calculated -> shows energy levels aren’t evenly spaced.

Question 3

What is the 1st ionisation energy?

Answer 3

= the energy required to remove one mole of e- (to infinity) from one of gaseous atoms to form one of gaseous 1+ ions.

Question 4

Does the 1st ionisation energy require energy?

Answer 4

Yes = endothermic because you are pulling apart between the e- and the positive nucleus.

Question 5

What are the trend for ionisation energies in the periodic table?
- why?

Answer 5

• Decreases going down a group: going down a group the energy of the subshell (from which the e- is removed) and the shielding increases
• Increases going across a period: across a period atomic radius decreases so there is a greater attraction between e- and the positive nucleus.

Question 6

What do successive ionisation energies prove?

Answer 6

The existence of quantum shells (s, p, d, f) because there is a large increase in ionisation from one shell to the next.

Question 7

What is the 1st electron affinity?

Answer 7

= the energy required to add one mole of e- to one mole of gaseous atoms to produce one mole of gaseous 1- ions.

Question 8

Do electron affinities require energy?

Answer 8

• 1st EA = exothermic/negative: gaining e- makes the system ore stable (great attraction between the positive nucleus + additional e-)
• The more exothermic the EA, the more stable the negative ion is formed

Question 9

What are the trend for electron affinity in the periodic table?

Answer 9

• Becomes less negative (exothermic) going down a group

- Becomes more negative (exothermic) going across a period

Question 10

What is an orbital?

Answer 10

= a region in space where there is a given (usually 95%) probability of finding a particular e-
-> the larger the quantum no. , the larger the orbital.

Question 11

What shape is a:

• S orbital?
• P orbital?

Answer 11

• S = spherical

- P = ‘figure of eight’ shaped = two lobes with a nodal plane

Question 12

What is a node?

Answer 12

= an area with no e-

Question 13

What are shells?

Answer 13

= principle energy levels in poly-electron atoms, referred to by the letters: K, L, M, N

• They correspond to the principle quantum no. n
• n = a number greater than 0
• n = the no. of the period
• K n=1, L n=2, M n=3, N n=4
• Shells contain multiple orbitals (except n=1)

Question 14

What are the principal quantum number?

- what does it indicate?

Answer 14

n = >0 = the period
Indicates:
- Distance of e- from the nucleus (the higher n the greater the distance)
- The e- energy (the high n the higher energy the e- has -> the further from the nucleus & easier to be removed)
- The no. of e- a shell can hold = 2n^2 e- maximum
e.g. L shell n=2 -> 2x2^2 = 8 e-

Question 15

What are subshells?

Answer 15

= a group of orbitals with the same (equivalent) energy, referred to by the letters: s (sharp), p (principle), d (diffuse), f (fundamental)

• Described by the Azimuthal/subsidiary quantum no. l
• l = 0 -> (n-1)

Question 16

What are the Azimuthal/subsidiary quantum numbers?

- what does it indicate?

Answer 16

l = 0 to (n-1)
Indicates:
- Which subshell an e- is in: l=0=s, l=1=p, l=2=d, l=3=f
- Energy of the subshell: energy increases as the vale of l increases
- Shape of the orbitals in that subshell: s=spherical, p=dumbell, d=more complex, f=even more complex
- The no. of e- a subshell can hold = 2(2l + 1)
e.g. l = 2 - d subshell that can hold 2(2x2 + 1) = 10 e-

Question 17

What are the magnetic quantum numbers?

- what does it represent/indicate?

Answer 17

m = range = -l to 0 to +l
e.g. p: l=1, m= -1 to +1 -> 3 values=3p orbitals
Represents:
- The no. orbitals in the subshell
Indicates:
- The direction of a particular orbital to the magnetic field/axis
- The orientation of individual orbitals within a subshell

Question 18

What are the spin quantum numbers?

- what do they describe?

Answer 18

s = -1/2 OR +1/2
Describes:
- The direction of the rotation of an e- around its own axis (self-rotation) as it moves around the nucleus.
- Clockwise spin (‘spin up’) = +1/2
- Anticlockwise spin (‘spin down’) = -1/2

• Orbitals have only 2 e- and they must have opposite spins (anti-parallel)

Question 19

What are the equations for working out all the quantum numbers?

Answer 19

Principle: n = period = >0
Azimuthal: l = 0 to (n-1)
Magnetic: m = -l to 0 to +l
Spin: s = -1/2 OR +1/2

Question 20

How many electrons can be in a shell?

Answer 20

2n^2

Question 21

How many electrons can be in a subshell?

Answer 21

2(2l + 1)

Question 22

What is Heisenberg’s Uncertainty principle?

Answer 22

= you cannot determine the position & momentum (velocity) of an e- at the same time.

Question 23

What is the Aufbas principle?

Answer 23

= e- enter at the lowest available energy level first.

Question 24

What is Hund’s rule of maximum multiplicity?

Answer 24

= when in orbitals of equal energy, e- will try to remain unpaired - minimises repulsion between like charges so they system is more stable.

Question 25

What is the Pauli exclusion principle?

Answer 25

= no two e- can have the same four quantum numbers (n, l, m, s) and only two e- can share an orbital provided they have an anti-parallel spin.

Question 26

What is the order for filling orbitals?

Answer 26

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

Question 27

What is Madeleines rule?

Answer 27

= Where you have two e- with equal n+l you fill the orbital with the lowest value of n first.