Bihar Board - Class 12 Physics - Chapter 12: Atom Handwritten Notes

The atom is the basic unit of matter, composed of a nucleus containing protons and neutrons, surrounded by electrons. The study of the atom has evolved from early atomic models to modern quantum mechanics, providing a deeper understanding of its structure, behavior, and interactions. This chapter explores atomic theory, models of the atom, and important concepts related to atomic structure and spectra.

Key Points

1. Historical Development of Atomic Theory

   • Dalton’s Atomic Theory: Proposed that matter is made up of indivisible atoms, each with a specific mass and properties.
   • Thomson’s Model (Plum Pudding Model): Discovered the electron and proposed that atoms are composed of a positively charged "pudding" with electrons embedded in it.
   • Rutherford’s Model: Based on the gold foil experiment, it showed that the atom has a small, dense nucleus and mostly empty space.
   • Bohr’s Model: Proposed that electrons orbit the nucleus in fixed paths or energy levels.

2. Structure of the Atom

   • Nucleus: Contains protons (positively charged) and neutrons (neutral), making it dense and positively charged.
   • Electrons: Negatively charged particles that orbit the nucleus in discrete energy levels or shells.
   • Atomic Number (Z): The number of protons in the nucleus, determining the element.
   • Mass Number (A): The total number of protons and neutrons in an atom.
   • Isotopes: Atoms of the same element with different numbers of neutrons, leading to different mass numbers.

3. Bohr’s Model of the Atom

   • Energy Levels: Electrons occupy discrete energy levels or orbits, each corresponding to a specific energy.
   • Quantization of Energy: Electrons can only occupy these energy levels, and energy is emitted or absorbed when an electron transitions between levels.
   • Spectral Lines: The emission and absorption of light by atoms result in distinct spectral lines, which are unique to each element.

4. Wave-Particle Duality of Electrons

   • Electrons exhibit both wave-like and particle-like behavior, as shown by the de Broglie hypothesis.
   • This behavior is central to the development of quantum mechanics and the understanding of atomic structure.

5. Quantum Mechanical Model of the Atom

   • Heisenberg Uncertainty Principle: It is impossible to simultaneously know both the position and momentum of an electron with complete certainty.
   • Schrödinger’s Wave Equation: Describes the probability distribution of an electron’s position within an atom.
   • Orbitals: Electrons do not follow fixed orbits but are found in regions of space called orbitals, each with a specific shape and energy.

6. Electron Configuration

   • Describes the arrangement of electrons in the atom's energy levels and orbitals.
   • Aufbau Principle: Electrons fill the lowest available energy levels first.
   • Pauli Exclusion Principle: No two electrons in an atom can have the same set of quantum numbers.
   • Hund’s Rule: Electrons fill degenerate orbitals (orbitals with the same energy) singly before pairing.

7. Atomic Spectra

   • When atoms absorb or emit energy, they produce characteristic spectral lines.
   • The hydrogen atom spectrum is often used to explain atomic transitions and the energy quantization of electrons.

Conclusion

The atom is the fundamental building block of matter, with a structure that has evolved from early models to the modern quantum mechanical understanding. Atomic theory explains the behavior of matter, the formation of elements, and the interactions between light and atoms. Understanding atomic structure is essential for exploring chemistry, physics, and the development of technologies such as lasers, semiconductors, and nuclear energy.

हिंदी के सभी अध्याय के महत्वपूर्ण प्रशन उत्तर के लिए अभी Download करें Vidyakul App - Free Download Click Here