All questions of Atomic Structure for UPSC CSE Exam

Understanding Atomic Models
The stability of an atom is a fundamental concept in atomic theory, and various models have attempted to explain it. Among these, Rutherford's model falls short in this regard.
Rutherford's Model Overview
- Proposed by Ernest Rutherford in 1911.
- Depicted the atom as a tiny, dense nucleus surrounded by orbiting electrons, similar to planets around the sun.
Why Doesn't Rutherford's Model Explain Stability?
- Electromagnetic Radiation: According to classical physics, an accelerating charge (like an electron in orbit) emits electromagnetic radiation. This means that as the electron spirals inwards, it would lose energy.
- Electron Collapse: Theoretically, as electrons lose energy, they should spiral into the nucleus, leading to atomic collapse. This scenario contradicts the observed stability of atoms.
- No Quantization: Rutherford's model lacks the principle of quantization, which is crucial for explaining the discrete energy levels of electrons. Without quantized orbits, electrons cannot maintain stable positions around the nucleus.
Comparison with Other Models
- Bohr’s Model: Introduced quantized orbits, which successfully explains the stability of atoms by allowing electrons to exist in specific energy levels without radiating energy.
- Thomson’s Model: Also known as the "plum pudding" model, it offered a different perspective but similarly failed to explain atomic stability effectively.
Conclusion
In summary, Rutherford's model does not adequately explain the stability of an atom due to its reliance on classical physics and the lack of quantization. This limitation highlights the need for more advanced models, such as Bohr's, to accurately describe atomic structure and behavior.

The present concept of the structure of an atom is given by which scientist?

The correct answer is option 'c) Niels Bohr'.

Explanation:

Niels Bohr was a Danish physicist who made significant contributions to the understanding of atomic structure and quantum theory. He is best known for his atomic model, also known as the Bohr model, which provided a new understanding of how electrons occupy energy levels around the nucleus of an atom.

Key Points:

- Rutherford: While Rutherford made important contributions to the understanding of atomic structure, his model did not provide a complete explanation of the behavior of electrons within an atom. Rutherford's model described the atom as having a small, dense, positively charged nucleus at the center, with electrons orbiting around it. However, his model could not explain why the electrons did not quickly spiral into the nucleus due to electromagnetic attraction.

- Goldstein: Goldstein, a German physicist, discovered the existence of positively charged particles called protons in 1886. However, his work did not provide a comprehensive model of the atom's structure.

- J.J. Thomson: Thomson, a British physicist, is known for his discovery of the electron in 1897. He proposed the "plum pudding" model of the atom, which suggested that electrons were evenly distributed within a positively charged sphere. However, this model was later disproven by Rutherford's experiments.

- Niels Bohr: In 1913, Bohr proposed his atomic model, which built upon Rutherford's previous work. He suggested that electrons occupy specific energy levels or orbits around the nucleus, and that they can jump between these energy levels by absorbing or emitting energy in discrete amounts. This model successfully explained the stability of atoms and the line spectra observed in various elements.

Conclusion:

In conclusion, the present concept of the structure of an atom is given by Niels Bohr. His atomic model, which introduced the idea of discrete energy levels for electrons, revolutionized our understanding of atomic structure and laid the foundation for further developments in quantum mechanics.

Understanding Hydrogen's Unique Nucleus
Hydrogen is the simplest and most abundant element in the universe. Its atomic structure is quite distinct compared to other elements.
Structure of Hydrogen
- Atomic Number: Hydrogen has an atomic number of 1, which means it has one proton in its nucleus.
- Neutrons: The most common isotope of hydrogen, known as protium, has no neutrons. This is a rare occurrence since most other elements have one or more neutrons in their nuclei.
Comparison with Other Elements
- Oxygen: Oxygen has an atomic number of 8, meaning it contains 8 protons and typically 8 neutrons in its most abundant isotope.
- Phosphorus: Phosphorus has an atomic number of 15, with 15 protons and usually 16 neutrons.
- Sodium: Sodium has an atomic number of 11, resulting in 11 protons and typically 12 neutrons.
Conclusion
- Unique Characteristic: Hydrogen's lack of neutrons in its most common form sets it apart from these other elements.
- Significance: This unique feature contributes to hydrogen's role in various chemical reactions and its fundamental importance in forming molecules, including water and organic compounds.
In summary, hydrogen is the only atom among the options provided that has a nucleus containing no neutrons, making it a fascinating subject in atomic theory and chemistry.