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Leaving Cert Physics & Chemistry: Energy levels & orbitals

How often Energy levels & orbitals comes up on the Physics & Chemistry papers, every year it was asked, and questions to try.

HL Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

OL Asked on 9 of the last 9 Ordinary Level papers, most recently in 2025. banker

Energy levels & orbitals, Higher Level(8 marks)

Quick ones on Energy levels & orbitals.

(a)Why does an excited atom emit light of only certain frequencies?
  1. Its electrons can have any amount of energy
  2. Electrons fall between fixed, discrete energy levels
  3. Its nucleus vibrates at set frequencies
(b)Flame test colour of potassium?
  1. Yellow-orange
  2. Crimson
  3. Lilac
(c)The visible lines of the hydrogen emission spectrum come from electrons falling to…
  1. The n = 2 level
  2. The n = 3 level
  3. The n = 1 level
Show the answers

(a) Electrons fall between fixed, discrete energy levels

(b) Lilac

(c) The n = 2 level

Your turn: Higher Level questions on Energy levels & orbitals.

Higher Level

Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025Q7(b), Q7(f), Q12(a)
2024Q7(b), Q7(c), Q8, Q12(a)
2023Q7(b), Q8
2022Q8
2021Q7(b), Q8
2019Q7(c), Q7(h), Q8
2018Q8
2017Q7(b), Q7(d), Q12(b)
2016Q7(d), Q7(e), Q8

Links open the State Examinations Commission’s paper for that year.

More Energy levels & orbitals questions

Energy levels & orbitals, 2 marks

The subsidiary (second) quantum number, l, describes the…

  1. Main energy level (the shell number)
  2. Spin of the electron (up or down)
  3. Shape of the orbital (the sublevel)
Show the answer

Shape of the orbital (the sublevel)

n gives the main level; l gives the sublevel and its shape (l = 0 is s, spherical; l = 1 is p, dumbbell); m gives orientation; the spin number gives spin.

Energy levels & orbitals, 3 marks

Hund's rule: electrons fill orbitals of equal energy…

  1. Only after the next main level is full
  2. Singly, with parallel spins, before any pairing
  3. In pairs, before starting a new orbital
Show the answer

Singly, with parallel spins, before any pairing

Electrons repel, so they spread out one per orbital in a sublevel before they pair up. That is why nitrogen's three 2p electrons are all unpaired.

Energy levels & orbitals, 2 marks

Possible values of the spin quantum number?

  1. +½ or −½
  2. 0 or 1
  3. 1, 2 or 3
Show the answer

+½ or −½

An electron can spin one of two ways, written +½ and −½. That is why an orbital can hold only two electrons.

Ordinary Level

Asked on 9 of the last 9 Ordinary Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025Q7(a), Q7(b), Q12(b)
2024Q7(b), Q8
2023Q7(c)
2022Q7(a), Q8
2021Q7(a)
2019Q7(a), Q7(c)
2018Q7(b), Q7(d), Q7(h)
2017Q7(b), Q7(c)
2016Q7(b)

Links open the State Examinations Commission’s paper for that year.

More Energy levels & orbitals questions

Energy levels & orbitals, 2 marks

Which colour does sodium give in a flame test?

  1. Lilac
  2. Green
  3. Yellow
Show the answer

Yellow

Sodium gives a strong yellow-orange flame; potassium gives lilac; lithium gives crimson. Each element has its own set of energy levels, so its own colour.

Energy levels & orbitals, 3 marks

Why does a metal salt give a coloured flame?

  1. The nucleus splits
  2. Electrons fall back to lower energy levels
  3. Electrons are removed from the nucleus
Show the answer

Electrons fall back to lower energy levels

Heat raises electrons to higher levels. When they fall back, the energy difference is given out as light of one frequency: E2 − E1 = hf.

Energy levels & orbitals, 2 marks

In E = hf, what is h?

  1. Planck's constant
  2. The height of the level
  3. The frequency
Show the answer

Planck's constant

h is Planck's constant and f is the frequency of the light. A bigger energy jump gives light of higher frequency.

Other Physics & Chemistry topics

All of Leaving Cert Physics & Chemistry