Atoms | Class 12 Physics Notes
By ConceptScroll Team · Published on 17 July 2026 · 2 min read
Atoms – this guide gives you a concise, exam-ready overview of Atoms from Class 12 Physics, written by ConceptScroll editors and reviewed against the latest NCERT textbook.
Wave nature of electrons and de Broglie hypothesis
The de Broglie hypothesis introduced the concept that particles such as electrons exhibit wave-like properties, characterized by a wavelength λ given by λ = h / p, where h is Planck's constant and p is the momentum of the particle. This wave-particle duality was a fundamental shift in understanding microscopic particles. For electrons in atoms, this implies that their motion can be described as standing waves around the nucleus. Bohr’s quantization condition can be interpreted as the requirement that an integral number of electron wavelengths fit along the circumference of the orbit, leading to stable standing waves. This explains why only certain orbits are allowed. The section includes a diagram showing a standing wave on a circular orbit where four de Broglie wavelengths fit into the circumference. This wave nature of electrons is the foundation of quantum mechanics and explains atomic stability and discrete energy levels.
📊 Diagram: See figure_10: FIGURE 12.8 A standing wave is shown on a circular orbit where four de Broglie wavelengths fit into the circumference of the orbit.
🧪 Activity: Verification of Bohr’s quantization condition using de Broglie wavelength calculations.
🔗 Connection: Summarizes the chapter and connects atomic structure to quantum mechanics.
Frequently asked questions
The angular momentum of an electron in the third orbit of an atom is
3.15 x 10 -34 Js
As an electron makes a transition from an excited state to the ground state of a hydrogen-like atom/ion
its kinetic energy increases but potential energy and total energy decreases
An alpha particle of energy 5 MeV is scattered through 180 0 by a fixed uranium nucleus. The distance of closest approach is of the order of
10 -12 cm
De Broglie’s hypothesis gave an explanation for Bohr’s quantised orbits by bringing in the wave particle duality. According to this, the orbits correspond to circular standing waves in which the circumference of the orbit is
an integral multiple of wavelength
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