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Leaving Cert Chemistry: Atomic structure

How often Atomic structure comes up on the Chemistry papers, every year it was asked, and questions to try.

HL Asked on 10 of the last 10 Higher Level papers, most recently in 2026. banker

OL Asked on 10 of the last 10 Ordinary Level papers, most recently in 2026. banker

June 2027 is the first exam on the new Chemistry course. These come from the 2016–2026 papers, so read them as a guide.

Atomic structure, Higher Level(6 marks)

Quick ones on Atomic structure.

(a)Relative charge on a neutron?
  1. +1
  2. 0
  3. -1
(b)Experiment that showed the atom has a small dense positive nucleus?
  1. Thomson's cathode ray experiment
  2. Millikan's oil drop experiment
  3. Rutherford's alpha particle scattering
(c)Mass number of an atom is the number of?
  1. Protons plus neutrons
  2. Neutrons only
  3. Protons plus electrons
Show the answers

(a) 0

(b) Rutherford's alpha particle scattering

(c) Protons plus neutrons

Your turn: Higher Level questions on Atomic structure.

Higher Level

Asked on 10 of the last 10 Higher Level papers, most recently in 2026. banker

Every paper, year by year

YearWhere it came up
2026Q4(a), Q4(b), Q4(e), Q10(a)
2025Q4(b), Q5
2024Q4(a), Q5
2023Q4(a), Q4(f), Q5
2022Q4(b), Q5
2021Q4(a), Q11(c)
2019Q4(a), Q10(b)
2018Q4(a), Q5, Q10(b)
2017Q4(b), Q10(b)
2016Q4(a), Q4(b), Q5

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

More Atomic structure questions

Atomic structure, 3 marks

Boron is 20% boron-10 and 80% boron-11. Relative atomic mass of boron?

  1. 10.5
  2. 10.2
  3. 10.8
Show the answer

10.8

RAM = (20 x 10 + 80 x 11) / 100 = (200 + 880) / 100 = 10.8. It lies nearer 11 because boron-11 is more common.

Atomic structure, 2 marks

In the equation Em - En = hf, what does h stand for?

  1. The gas constant
  2. Planck's constant
  3. Avogadro's constant
Show the answer

Planck's constant

h is Planck's constant. It links the energy gap between two levels to the frequency f of the light given out.

Atomic structure, 2 marks

Compared with a photon of red light, a photon of higher frequency carries?

  1. More energy
  2. Less energy
  3. The same energy
Show the answer

More energy

E = hf, so energy is proportional to frequency. Blue and violet light come from bigger energy gaps than red light.

Ordinary Level

Asked on 10 of the last 10 Ordinary Level papers, most recently in 2026. banker

Every paper, year by year

YearWhere it came up
2026Q4(a), Q4(e), Q4(f)
2025Q5, Q10(b)
2024Q4(c), Q10(c), Q11(a)
2023Q4(a), Q5
2022Q10(a)
2021Q4(a), Q10(a)
2019Q4(a), Q11(a)
2018Q10(b), Q11(a)
2017Q4(b), Q5
2016Q4(b), Q5

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

More Atomic structure questions

Atomic structure, 2 marks

Atomic number is the number of?

  1. Protons plus neutrons in the nucleus
  2. Neutrons in the nucleus of an atom
  3. Protons in the nucleus of an atom
Show the answer

Protons in the nucleus of an atom

The atomic number identifies the element. Protons plus neutrons is the mass number.

Atomic structure, 2 marks

Why is the relative atomic mass of chlorine 35.5 and not a whole number?

  1. It was measured inaccurately, and the error was never corrected
  2. It is an average of its isotopes, chlorine-35 and chlorine-37
  3. Chlorine atoms each contain half a neutron in the nucleus
Show the answer

It is an average of its isotopes, chlorine-35 and chlorine-37

About three quarters of chlorine atoms are chlorine-35 and one quarter chlorine-37. The average mass is 35.5.

Atomic structure, 2 marks

Who discovered the electron using cathode rays?

  1. J.J. Thomson
  2. James Chadwick
  3. John Dalton
Show the answer

J.J. Thomson

Thomson showed cathode rays were streams of tiny negative particles, later called electrons.

Other Chemistry topics

All of Leaving Cert Chemistry