1. An atom is the smallest unit of matter that retains the properties of an element.
  2. It consists of a nucleus at the center and electrons orbiting around it.
  3. The nucleus contains protons (positively charged particles) and neutrons (neutral particles).
  4. Electrons are negatively charged and occupy distinct energy levels or shells.
  5. Atoms are electrically neutral because the number of protons equals the number of electrons.

Discovery of Electrons

  1. J.J. Thomson discovered the electron in 1897 using a cathode ray tube experiment.
  2. Cathode rays were shown to be streams of negatively charged particles, later named electrons.
  3. Thomson proposed the plum pudding model, which suggested that electrons are embedded in a positively charged sphere.

Discovery of Protons

  1. Protons were discovered by Eugen Goldstein in the late 19th century through canal ray experiments.
  2. Canal rays (positive rays) were found to be made of positively charged particles, now known as protons.
  3. Protons have a charge equal in magnitude to the electron but with the opposite sign.

Discovery of Neutrons

  1. James Chadwick discovered the neutron in 1932.
  2. Neutrons are neutral particles with no electrical charge, found in the nucleus.
  3. They play a critical role in adding mass to the atom and stabilizing the nucleus.

Atomic Models

  1. Rutherford’s Model: Discovered the nucleus and proposed that most of the atom’s mass is concentrated in a small, dense, positively charged nucleus.
  2. Bohr’s Model: Introduced the concept of quantized energy levels for electrons.
  3. Quantum Mechanical Model: The current model describes electrons as existing in orbitals, regions of space with the highest probability of finding an electron.

Key Properties of Subatomic Particles

  1. Electrons: Negative charge, very small mass (1/1836 the mass of a proton).
  2. Protons: Positive charge, mass approximately equal to one atomic mass unit (AMU).
  3. Neutrons: No charge, mass slightly greater than that of a proton.

Applications and Importance

  1. Understanding atomic structure is crucial for explaining chemical reactions and bonding.
  2. Atomic theory forms the foundation of modern physics and quantum mechanics.
  3. Research on atomic structure has led to advancements in nuclear energy and medical imaging.
  4. The discovery of subatomic particles paved the way for the development of particle physics.

Category

Questions

  1. Who discovered the electron?
  2. What is the charge of a proton?
  3. Who proposed the nuclear model of the atom?
  4. What is the mass of a neutron compared to a proton?
  5. What particle did James Chadwick discover?
  6. What subatomic particle has the smallest mass?
  7. What is the relative charge of an electron?
  8. Who discovered the proton?
  9. What is the nucleus of an atom composed of?
  10. What is the primary function of neutrons in an atom?
  11. What model of the atom was proposed by J.J. Thomson?
  12. In Rutherford’s experiment, what particle was used to probe the structure of the atom?
  13. What does the atomic number of an element represent?
  14. What is the approximate size of the nucleus compared to the size of the atom?
  15. What discovery led to the rejection of the plum pudding model?
  16. What holds the nucleus of an atom together?
  17. Which experiment led to the discovery of the nucleus?
  18. What is the charge of a neutron?
  19. What determines the chemical properties of an atom?
  20. What is the mass number of an atom?
  21. Who proposed the quantum mechanical model of the atom?
  22. What part of the atom contains most of its mass?
  23. What experiment demonstrated the existence of the electron?
  24. What is the charge-to-mass ratio of an electron?
  25. What property differentiates isotopes of the same element?
  26. What defines an ion?
  27. What happens to an atom when it gains an electron?
  28. What is the main limitation of Rutherford’s atomic model?
  29. How many electrons can occupy the first energy level of an atom?
  30. What term describes atoms with the same atomic number but different mass numbers?
  31. Who proposed the planetary model of the atom?
  32. What particle is responsible for the chemical bonding of atoms?
  33. What is the lightest subatomic particle?
  34. What is the purpose of the atomic mass unit (amu)?
  35. Which force keeps electrons bound to the nucleus?
  36. What happens to the size of an atom as the number of protons increases?