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Leaving Cert Physics & Chemistry: Atomic structure

How often Atomic structure 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

Atomic structure, Higher Level(7 marks)

Quick ones on Atomic structure.

(a)Isotopes are atoms of the same element with…
  1. The same mass number but different atomic numbers
  2. The same atomic number but different mass numbers
  3. The same neutron number, different proton numbers
(b)How many neutrons are in an atom of chlorine-37? (atomic number 17)
  1. 37
  2. 17
  3. 20
(c)An element has two isotopes: mass 63 (70%) and mass 65 (30%). Relative atomic mass?
  1. 63.6
  2. 64.4
  3. 64.0
Show the answers

(a) The same atomic number but different mass numbers

(b) 20

(c) 63.6

Your turn: Higher Level questions on Atomic structure.

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(a), Q7(c)
2024Q7(j), Q8
2023Q7(a), Q7(c)
2022Q7(a), Q7(b), Q7(c)
2021Q7(a), Q12(b)
2019Q7(a), Q7(b)
2018Q7(a), Q7(b)
2017Q7(a), Q8
2016Q7(a), Q7(b)

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

More Atomic structure questions

Atomic structure, 2 marks

The atomic number of an element is the number of…

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

Protons in the nucleus

Atomic number (Z) = number of protons. It fixes which element an atom is. Protons plus neutrons is the mass number.

Atomic structure, 2 marks

Where is almost all the mass of an atom found?

  1. Spread evenly through the atom
  2. In the nucleus
  3. In the electron cloud
Show the answer

In the nucleus

The protons and neutrons in the tiny nucleus carry nearly all the mass. The electrons around it take up most of the volume but add very little mass.

Atomic structure, 3 marks

A sodium ion (Na+) and a neon atom both have 10 electrons. What is different about them?

  1. The number of protons
  2. The number of electrons
  3. Nothing: they are identical
Show the answer

The number of protons

Na has 11 protons and loses one electron to become Na+ (10 electrons). Neon has 10 protons and 10 electrons. Same electron count, different nuclear charge, so different particles.

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(c), Q8
2024Q7(a), Q7(d)
2023Q8
2022Q8
2021Q7(c), Q7(g)
2019Q7(b)
2018Q7(a), Q8
2017Q7(e), Q8
2016Q7(e), Q8, Q12(c)

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

More Atomic structure questions

Atomic structure, 2 marks

Charge and relative mass of a proton?

  1. Charge −1, relative mass 1/1840
  2. Charge 0, relative mass 1
  3. Charge +1, relative mass 1
Show the answer

Charge +1, relative mass 1

Protons (+1, mass 1) and neutrons (0, mass 1) are in the nucleus. Electrons (−1, about 1/1840) move around it.

Atomic structure, 2 marks

Mass number is?

  1. Number of protons plus electrons
  2. Number of protons plus neutrons
  3. Number of protons only
Show the answer

Number of protons plus neutrons

Mass number counts the particles in the nucleus. The number of protons alone is the atomic number.

Atomic structure, 2 marks

Isotopes are atoms of the same element with different numbers of?

  1. Neutrons
  2. Protons
  3. Electrons in the neutral atom
Show the answer

Neutrons

Isotopes have the same atomic number but different mass numbers. Carbon-12 and carbon-14 both have 6 protons but 6 and 8 neutrons.

Other Physics & Chemistry topics

All of Leaving Cert Physics & Chemistry