ROUTERA

Atoms

Class 12th Physics Chapter Case Study

Case Study 1: Structure of the Atom

The atom is the basic unit of matter, composed of protons, neutrons, and electrons. The nucleus, containing protons and neutrons, is surrounded by electrons that occupy specific energy levels or shells. The atomic number defines the number of protons in the nucleus, while the mass number is the sum of protons and neutrons.

Questions:

  1. What particles are found in the nucleus of an atom?
    • a) Protons and electrons
    • b) Protons and neutrons
    • c) Neutrons and electrons
    • d) Only protons
  2. The atomic number of an element is defined as the number of:
    • a) Neutrons
    • b) Electrons
    • c) Protons
    • d) Protons and neutrons
  3. Which of the following statements about electrons is correct?
    • a) They are found in the nucleus.
    • b) They have a positive charge.
    • c) They occupy energy levels outside the nucleus.
    • d) They contribute significantly to the mass of the atom.
  4. If an atom has 6 protons and 8 neutrons, what is its mass number?
    • a) 6
    • b) 14
    • c) 8
    • d) 4

Answers:

  1. b) Protons and neutrons
  2. c) Protons
  3. c) They occupy energy levels outside the nucleus.
  4. b) 14

Case Study 2: Rutherford's Gold Foil Experiment

Ernest Rutherford's gold foil experiment led to the discovery of the atomic nucleus. In this experiment, a thin foil of gold was bombarded with alpha particles. Most particles passed through, but a few were deflected at large angles, indicating a small, dense, positively charged nucleus.

Questions:

  1. What did Rutherford conclude from his gold foil experiment?
    • a) Atoms are solid spheres.
    • b) Atoms have a large empty space with a small nucleus.
    • c) Electrons are located in the nucleus.
    • d) All alpha particles are absorbed by the foil.
  2. The deflection of alpha particles in the experiment indicated the presence of:
    • a) Electrons
    • b) Nucleus
    • c) Neutrons
    • d) Quarks
  3. In Rutherford's model of the atom, electrons are located:
    • a) Inside the nucleus
    • b) In fixed orbits around the nucleus
    • c) Randomly distributed within the atom
    • d) In energy shells outside the nucleus
  4. Which of the following statements about the nucleus is correct based on Rutherford's findings?
    • a) It contains most of the atom's volume.
    • b) It is negatively charged.
    • c) It is very dense and small compared to the entire atom.
    • d) It contains only neutrons.

Answers:

  1. b) Atoms have a large empty space with a small nucleus.
  2. b) Nucleus
  3. d) In energy shells outside the nucleus
  4. c) It is very dense and small compared to the entire atom.

Case Study 3: Bohr's Model of the Atom

Niels Bohr proposed a model of the atom that introduced quantized energy levels for electrons. According to Bohr, electrons orbit the nucleus at specific distances, and energy is emitted or absorbed when electrons move between these levels. This model successfully explained the spectral lines of hydrogen.

Questions:

  1. According to Bohr's model, electrons move in:
    • a) Random paths
    • b) Fixed orbits with quantized energies
    • c) Circular paths only
    • d) Elliptical orbits around the nucleus
  2. When an electron jumps from a higher energy level to a lower one, it:
    • a) Absorbs energy
    • b) Emits energy in the form of light
    • c) Loses mass
    • d) Becomes a proton
  3. What is the main limitation of Bohr's model?
    • a) It only explains hydrogen atom spectra.
    • b) It does not consider the wave nature of electrons.
    • c) It assumes electrons have fixed positions.
    • d) All of the above.
  4. The energy levels in Bohr's model are:
    • a) Continuous
    • b) Discrete and quantized
    • c) Determined by temperature
    • d) Variable and random

Answers:

  1. b) Fixed orbits with quantized energies
  2. b) Emits energy in the form of light
  3. d) All of the above.
  4. b) Discrete and quantized

Case Study 4: Quantum Mechanical Model of the Atom

The quantum mechanical model, developed by Schrödinger and others, describes the atom in terms of probabilities. Electrons are treated as wave functions, and their positions are represented by orbitals. This model incorporates the dual nature of electrons and provides a more accurate description of atomic behavior.

Questions:

  1. In the quantum mechanical model, electrons are described as:
    • a) Particles only
    • b) Waves only
    • c) Both particles and waves
    • d) Fixed points around the nucleus
  2. What does the term 'orbital' refer to in the quantum mechanical model?
    • a) A specific path taken by an electron
    • b) A region of space where the probability of finding an electron is high
    • c) The nucleus of the atom
    • d) The mass of an electron
  3. Which principle states that it is impossible to know both the position and momentum of an electron simultaneously?
    • a) Pauli exclusion principle
    • b) Heisenberg uncertainty principle
    • c) Aufbau principle
    • d) Hund's rule
  4. The shapes of electron orbitals are determined by:
    • a) The energy of the electron
    • b) The charge of the nucleus
    • c) The quantum numbers associated with the electron
    • d) The mass of the electron

Answers:

  1. c) Both particles and waves
  2. b) A region of space where the probability of finding an electron is high
  3. b) Heisenberg uncertainty principle
  4. c) The quantum numbers associated with the electron

Case Study 5: Atomic Models and Spectra

The atomic spectrum of an element consists of distinct lines, each corresponding to specific energy transitions of electrons. When electrons move between energy levels, they emit or absorb photons with energies equal to the difference between these levels, producing the characteristic spectrum of the element.

Questions:

  1. The lines in an atomic spectrum are produced due to:
    • a) The movement of the nucleus
    • b) The transition of electrons between energy levels
    • c) The interaction of atoms with magnetic fields
    • d) The temperature of the substance
  2. What determines the color of light emitted in an atomic spectrum?
    • a) The mass of the electron
    • b) The energy difference between the electron energy levels
    • c) The type of atom
    • d) Both b and c
  3. Which of the following transitions would result in the emission of a photon with the highest energy?
    • a) n = 1 to n = 2
    • b) n = 2 to n = 3
    • c) n = 3 to n = 1
    • d) n = 2 to n = 1
  4. The hydrogen spectrum is primarily observed as a:
    • a) Continuous spectrum
    • b) Line spectrum
    • c) Band spectrum
    • d) Electromagnetic spectrum

Answers:

  1. b) The transition of electrons between energy levels
  2. d) Both b and c
  3. c) n = 3 to n = 1
  4. b) Line spectrum