Who this is for: Cambridge IGCSE Physics (0625) students who can label protons and neutrons but lose marks on isotope definitions, Rutherford scattering evidence, or confusing atomic and mass numbers.
What query it owns: how to understand and revise the nuclear model of an atom in Cambridge IGCSE Physics.
Why this is safe: this page owns the nuclear-model revision-guide angle, while Tutopiya’s Nuclear Model of an Atom subtopic page owns the learning resource and the free Nuclear Model quiz owns the practice.

The nuclear model of an atom describes a tiny, dense, positively charged nucleus surrounded by electrons in mostly empty space. Cambridge IGCSE Physics (0625) tests whether you can state subatomic particle properties, define isotopes, and explain what Rutherford’s alpha-particle scattering experiment proved. This guide covers the syllabus pathway and exam wording.

Key takeaways

• Proton: charge +1, mass ≈ 1 u, in nucleus. Neutron: charge 0, mass ≈ 1 u, in nucleus. Electron: charge −1, negligible mass, in shells.
• Atomic number (Z) = number of protons. Mass number (A) = protons + neutrons.
• Isotopes = same proton number, different neutron number (same element, different mass).
• Rutherford scattering showed most of the atom is empty space with a small dense nucleus.
• Electrons are held by electrostatic attraction to the positive nucleus.

What is the nuclear model of an atom in Cambridge IGCSE Physics?

The nuclear model is the description of an atom as a central nucleus (protons and neutrons) with electrons orbiting in shells. It replaced the plum-pudding model after Rutherford’s experiment showed alpha particles could be deflected through large angles. You must know particle charges, relative masses, and how isotopes differ. Read the full notes on Tutopiya’s Nuclear Model of an Atom subtopic page before attempting questions.

The core ideas you must master

Particle	Relative charge	Relative mass	Location
Proton	+1	1	Nucleus
Neutron	0	1	Nucleus
Electron	−1	≈ 1/1840 (negligible)	Shells / orbitals

Atomic notation and isotopes — worked table

Notation	Protons (Z)	Neutrons (N)	Electrons (neutral atom)	Isotope of…
¹²₆C	6	6	6	Carbon
¹⁴₆C	6	8	6	Carbon (isotope of ¹²C)
³⁵₁₇Cl	17	18	17	Chlorine
³⁷₁₇Cl	17	20	17	Chlorine (isotope of ³⁵Cl)

Isotope definition: atoms of the same element (same proton number) with different numbers of neutrons.

Rutherford scattering — evidence table

Observation	Conclusion
Most alpha particles pass straight through	Atom is mostly empty space
Some alpha particles deflected through small angles	Positive charge is not uniformly spread
Very few alpha particles bounce back (~180°)	Mass and positive charge concentrated in a tiny nucleus
Nucleus is much smaller than the atom	Electrons orbit at large distances compared to nucleus size

Nuclear model in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical nuclear-model stem
Define	Precise syllabus definition	”Define the term isotope.”
State	Short factual answer	”State the charge on a neutron.”
Describe	Structure or experiment	”Describe the nuclear model of the atom.”
Explain	Cause and effect	”Explain what Rutherford’s experiment showed.”
Calculate	Use A = Z + N	”Calculate the number of neutrons in ²³₁₁Na.”

Worked exam-style stems (how to answer the wording)

1. “Define the term isotope.” Atoms of the same element with the same number of protons but different numbers of neutrons. Reward: mentions same proton number AND different neutron number.
2. “An atom has mass number 23 and atomic number 11. State the number of protons, neutrons and electrons (neutral atom).” Protons = 11, neutrons = 23 − 11 = 12, electrons = 11. Reward: correct subtraction for neutrons.
3. “Explain why most alpha particles passed straight through the gold foil.” The atom is mostly empty space; the nucleus is tiny compared to the atom’s size. Reward: links observation to empty space, not just “thin foil”.

When you can recognise the wording instantly, work the Nuclear Model quiz and connect to Radioactivity for unstable nuclei.

How the nuclear model connects to the rest of the syllabus

The nuclear model is the foundation for Radioactivity — unstable nuclei, decay and radiation types. The Cambridge IGCSE Physics resource hub links every Nuclear Physics subtopic.

Common mistakes students make

• Defining isotopes as “different mass number” without stating same proton number.
• Confusing atomic number with mass number.
• Stating electrons have significant mass (mass is negligible).
• Saying Rutherford proved electrons orbit in fixed shells (he proved a nucleus exists; shell detail came later).
• Calculating neutrons as A + Z instead of A − Z.

When you need more support

If isotope and Rutherford questions keep costing marks, work through the Nuclear Model quiz, then get focused help from a Cambridge IGCSE Physics tutor.

Frequently asked questions

Is the nuclear model hard in Cambridge IGCSE Physics? The particle table is straightforward; marks are lost on incomplete isotope definitions and weak Rutherford explanations.

What is the difference between atomic number and mass number? Atomic number = protons; mass number = protons + neutrons.

Do isotopes have different chemical properties? No — same electron arrangement (same proton number); physical properties such as density can differ.

How do I revise the nuclear model effectively? Memorise particle properties, practise isotope calculations, explain Rutherford’s three observations, then take the Nuclear Model quiz.

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