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Leaving Cert Physics & Chemistry: Periodic table & ionisation energy

How often Periodic table & ionisation energy 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

Periodic table & ionisation energy, Higher Level(7 marks)

Quick ones on Periodic table & ionisation energy.

(a)First ionisation energy: the minimum energy to remove the most loosely bound electron from…
  1. One atom in the solid element
  2. One mole of isolated gaseous atoms
  3. One mole of ions in solution
(b)Why does first ionisation energy generally increase across a period?
  1. Screening by inner electrons rises sharply
  2. More electron shells are added
  3. Nuclear charge rises and atomic radius falls
(c)A transition metal is an element that…
  1. Forms at least one ion with an incomplete d sublevel
  2. Is found in Group 1 or Group 2
  3. Has a completely full d sublevel in all its ions
Show the answers

(a) One mole of isolated gaseous atoms

(b) Nuclear charge rises and atomic radius falls

(c) Forms at least one ion with an incomplete d sublevel

Your turn: Higher Level questions on Periodic table & ionisation energy.

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

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

More Periodic table & ionisation energy questions

Periodic table & ionisation energy, 2 marks

Many transition metals and their compounds are useful as…

  1. Electrical insulators
  2. Soft, low-density metals
  3. Catalysts
Show the answer

Catalysts

Transition metals (for example iron, nickel and platinum) and their compounds often act as catalysts. They also form coloured compounds and ions of variable valency.

Periodic table & ionisation energy, 2 marks

How does atomic radius change across a period, from left to right?

  1. It stays the same
  2. It decreases
  3. It increases
Show the answer

It decreases

Across a period, nuclear charge increases while electrons go into the same main level, so they are pulled in more tightly and the atoms get smaller.

Periodic table & ionisation energy, 3 marks

Compared with a chlorine atom, a chloride ion (Cl-) is…

  1. Larger
  2. Smaller
  3. The same size
Show the answer

Larger

Cl- has one extra electron but the same 17 protons. The extra repulsion between electrons makes the ion spread out, so it is larger than the atom.

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

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

More Periodic table & ionisation energy questions

Periodic table & ionisation energy, 2 marks

Elements in the modern periodic table are arranged in order of increasing?

  1. Mass number
  2. Date of discovery
  3. Atomic number
Show the answer

Atomic number

Mendeleev used atomic mass, but the modern table uses atomic number (number of protons). That fixed the few places where mass order was wrong.

Periodic table & ionisation energy, 2 marks

Elements in the same group have the same number of?

  1. Energy levels
  2. Outer electrons
  3. Neutrons
Show the answer

Outer electrons

Same outer electrons means similar chemistry. Elements in the same period have the same number of occupied energy levels.

Periodic table & ionisation energy, 2 marks

Group 1 metals such as sodium and potassium are called?

  1. Alkali metals
  2. Halogens
  3. Noble gases
Show the answer

Alkali metals

They react with water to form alkaline solutions. Halogens are Group 7; noble gases are Group 0 (or 18).

Other Physics & Chemistry topics

All of Leaving Cert Physics & Chemistry