2.2 Development of the Atomic Model

Short Answer Questions

1. Who first proposed the concept of the atom?
   Answer
   Democritus
2. What does the term “atomos” mean?
   Answer
   Indivisible or uncuttable
3. What was a key feature of Dalton’s atomic model?
   Answer
   Atoms are indivisible and cannot be created or destroyed in a chemical reaction.
4. What subatomic particle did J.J. Thomson discover?
   Answer
   Electron
5. What is the name of Thomson’s atomic model?
   Answer
   Plum pudding model
6. What experiment did Rutherford conduct?
   Answer
   Gold foil experiment
7. What is the nucleus of an atom?
   Answer
   A tiny, dense, positively charged center of an atom that contains protons and neutrons.
8. What did Bohr introduce in his atomic model?
   Answer
   Electron shells or energy levels
9. What subatomic particle did Chadwick discover?
   Answer
   Neutron
10. Where are protons located in an atom?
    Answer
    In the nucleus
11. What is the charge of a neutron?
    Answer
    Neutral (0 charge)
12. What is the charge of an electron?
    Answer
    -1
13. Where are electrons located in an atom?
    Answer
    In shells or energy levels around the nucleus
14. What is the relative mass of a proton?
    Answer
    1
15. What is the relative mass of an electron?
    Answer
    1/1840 (negligible compared to protons and neutrons)
16. What is the maximum number of electrons that the first shell can hold?
    Answer
    2
17. What is the maximum number of electrons that the second shell can hold?
    Answer
    8
18. What is the outermost shell of an atom called?
    Answer
    Valence shell
19. What are valence electrons?
    Answer
    Electrons in the outermost shell of an atom
20. What is the nucleon number?
    Answer
    The total number of protons and neutrons in an atom's nucleus.

Explanation Questions

1. How did Thomson’s atomic model differ from Dalton’s model?
   Answer
   Thomson's model proposed that atoms contain negatively charged electrons embedded in a positively charged sphere (plum pudding model), whereas Dalton believed that atoms were indivisible solid spheres.
2. Describe the key findings of Rutherford’s gold foil experiment.
   Answer
   Rutherford's experiment showed that most of the atom is empty space, and a dense, positively charged nucleus is present at the center, which deflected some alpha particles.
3. How did Bohr’s atomic model improve upon Rutherford’s model?
   Answer
   Bohr introduced the concept of electron shells, where electrons orbit the nucleus in fixed energy levels instead of moving randomly around the nucleus.
4. What are the three subatomic particles of an atom?
   Answer
   Protons, neutrons, and electrons.
5. Why is the mass of an electron considered negligible compared to protons and neutrons?
   Answer
   The mass of an electron is 1/1840 of a proton or neutron, making it negligible in atomic mass calculations.
6. Explain the significance of the nucleus in an atom.
   Answer
   The nucleus contains protons and neutrons, determines the atomic number, and accounts for most of the atom’s mass.
7. How is the atomic number of an element determined?
   Answer
   The atomic number is determined by the number of protons in the nucleus of an atom.
8. Explain the role of electron shells in the atomic model.
   Answer
   Electron shells determine the energy levels of electrons, affecting chemical bonding and reactivity.
9. How are electron arrangements related to the chemical properties of an element?
   Answer
   The number and arrangement of valence electrons influence an element's chemical properties, including its reactivity and bonding behavior.
10. Explain the relationship between the development of the atomic model and the advancement of scientific knowledge.
    Answer
    Each atomic model evolved as new experimental evidence was discovered, reflecting the continuous progress of scientific understanding.