General Chemistry I - Lecture 1: Models of Atom
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Questions and Answers

What was the primary hypothesis tested by Rutherford's gold foil experiment?

  • Atoms consist solely of electrons.
  • Atoms are indivisible.
  • Atoms contain a dense nucleus. (correct)
  • Atoms have equal numbers of protons and electrons.

    • Thomson's model proposed that protons and electrons are uniformly mixed throughout the atom.

    True (A)

    What did Rutherford conclude about the density of the atom based on his experiments?

    The atom is mostly empty space.

    The nucleus contains a positive charge and most of the ______ of the atom.

    <p>mass</p> Signup and view all the answers

    Match the following models of the atom with their main proponents:

    <p>Thomson’s model = J.J. Thomson Rutherford’s model = Ernest Rutherford Bohr’s model = Niels Bohr Gold foil experiment = Ernest Rutherford</p> Signup and view all the answers

    Which of the following statements is true regarding the findings of the gold foil experiment?

    <p>Most alpha particles passed straight through the gold foil. (C)</p> Signup and view all the answers

    According to Rutherford's model, the nucleus is larger than the entire atom.

    <p>False (B)</p> Signup and view all the answers

    What particles were primarily targeted in Rutherford's gold foil experiment?

    <p>Alpha particles</p> Signup and view all the answers

    What was a key limitation of Rutherford's model of the atom?

    <p>It couldn't explain atomic spectra (C)</p> Signup and view all the answers

    Bohr’s model of the atom states that electrons can exist in any energy state.

    <p>False (B)</p> Signup and view all the answers

    What change occurs when an atom transitions from a high-energy state to a lower energy state?

    <p>It emits a quantum of radiation.</p> Signup and view all the answers

    According to Bohr's model, the angular momentum of the electron is quantized in integral multiples of _____.

    <p>h/2π</p> Signup and view all the answers

    Which postulate of Bohr's model is entirely incorrect?

    <p>Electrons radiate in a circular orbit (A)</p> Signup and view all the answers

    Match the following models with their respective features:

    <p>Rutherford's Model = Failed to explain atomic stability Bohr's Model = Electrons occupy fixed energy levels Modern Quantum Theory = Describes electrons as wave functions</p> Signup and view all the answers

    The _____ force between the electron and nucleus must be balanced by the centrifugal force for mechanical stability in the Bohr model.

    <p>Coulombic</p> Signup and view all the answers

    What happens to an electron when it is in a stationary state according to Bohr’s model?

    <p>It does not radiate energy.</p> Signup and view all the answers

    Flashcards

    Thomson's model of atom

    Protons and electrons are uniformly mixed throughout the atom.

    Rutherford's gold foil experiment

    Experiment to test Thomson's model using alpha particles and gold foil.

    Alpha particles

    Positively charged particles used in Rutherford's experiment.

    Atom's empty space

    Most of the atom's volume is empty space, not filled with matter.

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    Atomic nucleus

    Small, dense, positively charged center of the atom.

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    Rutherford's model conclusion

    Atom is mostly empty space, with a dense positive nucleus.

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    Subatomic particles

    Particles smaller than an atom (e.g., protons, neutrons, electrons).

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    Gold foil

    Material used in Rutherford's experiment to detect alpha particle scattering.

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    Rutherford's atomic model flaws

    Rutherford's model couldn't explain atomic stability or spectra using classical physics.

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    Nuclear atom instability

    Classical physics predicted a nuclear atom would be unstable due to electron movement and radiation.

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    Bohr's atomic model

    An atomic model proposing stationary states with fixed energy for electrons.

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    Electron radiation (Bohr)

    Atoms radiate energy when electrons transition between energy levels (higher to lower).

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    Allowed electron motion (Bohr)

    Electron's angular momentum must be a multiple of h/2π.

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    Bohr model postulate accuracy

    The first two Bohr postulates are largely accurate, while the third is not, and the fourth is partially correct.

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    Balance of forces in Bohr model

    Coulomb force and centrifugal force balance to stabilize the electron orbit.

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    Modern Quantum theory

    A refined model of electron behavior that corrected the inaccuracies of Bohr's model

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    Study Notes

    General Chemistry I - Lecture 1: Models of Atom

    • Lecture delivered by Dr. Mahmoud A. A. Ibrahim, Chemistry Department, Faculty of Science, Minia University
    • Lecture number 1 covers atomic models
    • Models of the atom include Thomson's, Rutherford's, and Bohr's models

    Thomson's Model

    • Developed in 1911, after the components of the atom (protons and electrons) were discovered
    • Proposed a model where protons and electrons are mixed uniformly throughout the atom

    Rutherford's Model

    • Rutherford tested Thomson's hypothesis with the gold foil experiment
    • Bombardment of a gold foil with alpha particles (Helium nuclei)
    • Observations:
      • Most alpha particles passed straight through the foil
      • Some alpha particles were deflected slightly
      • Very few alpha particles were deflected greatly
      • Even fewer bounced off the foil and back
    • Conclusions:
      • The atom is mostly empty space
      • The nucleus is small, dense, and positively charged
      • The nucleus contains most of the atom's mass, and is 100,000 times smaller than the atom

    Rutherford's Model Difficulty

    • The model failed to explain the stability of atoms and atomic spectra from the classical viewpoint

    Bohr's Model

    • Developed two years after Rutherford's model
    • Proposed that electrons are in stationary states of motion with fixed energies
    • Electrons do not radiate when in these stationary states
    • When an electron changes energy levels, it emits or absorbs a quantum of radiation, equal to the difference in energy between the levels
    • Electrons orbit the nucleus in circular orbits
    • Angular momentum of electrons is an integral multiple of h/2π
    • Bohr's postulates, while initially accepted, are partly or entirely incorrect by modern quantum theory standards

    Bohr's Model Derivation of Energy States

    • The derivation of energy state expressions is straightforward
    • Mechanical stability requires balancing Coulombic and centrifugal forces
    • Coulombic force = Centrifugal force = (Ze2)/(4πε0r2) = mv2/r

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    Related Documents

    General Chemistry I Lecture Notes PDF

    Description

    In this quiz, explore the different atomic models presented in General Chemistry I, including Thomson's, Rutherford's, and Bohr's models. Test your understanding of the historical development and significance of these models in the context of atomic theory. This lecture sets the foundation for further studies in chemistry.

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