Nuclei | Class 12 Physics Notes
By ConceptScroll Team · Published on 17 July 2026 · 2 min read
Nuclei – this guide gives you a concise, exam-ready overview of Nuclei from Class 12 Physics, written by ConceptScroll editors and reviewed against the latest NCERT textbook.
13.1 INTRODUCTION
This section revisits the concept of the atomic nucleus introduced in the previous chapter. It emphasizes that the nucleus is the central part of the atom where positive charge and most of the mass are concentrated. The size of the nucleus is extremely small compared to the atom itself. Experiments involving the scattering of alpha-particles showed that the radius of the nucleus is smaller than the radius of the atom by a factor of about 10^4. Consequently, the volume of the nucleus is approximately 10^-12 times the volume of the atom, indicating that an atom is mostly empty space. For analogy, if an atom were enlarged to the size of a classroom, its nucleus would be the size of a pinhead. Despite its small size, the nucleus contains more than 99.9% of the atom's mass. The section raises fundamental questions about the structure and constituents of the nucleus and how these constituents are held together. The chapter aims to explore these questions by discussing nuclear properties such as size, mass, stability, and nuclear phenomena including radioactivity, fission, and fusion.
🔗 Connection: Leads to the next section which discusses atomic masses and the composition of the nucleus, including isotopes and the discovery of the neutron.
Frequently asked questions
When a nucleus in an atom undergoes a radioactive decay, the electronic energy levels of the atom
change for α and β radioactivity but not for gamma-radioactivity.
Heavy stable nuclei have more neutrons than protons. This is because of the fact that
electrostatic forces between protons are repulsive
Which of the following statements is true for nuclear forces?
They are short-range forces
Nuclides with same neutron number N but different atomic Number Z, are called
Isotones
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