Early Atomic Theory and Electron Discovery
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Early Atomic Theory and Electron Discovery

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Questions and Answers

What did Rutherford conclude must exist in the center of the atom based on his experiments with alpha particles?

  • A concentrated positive charge (correct)
  • An electron cloud
  • High energy levels
  • A concentrated negative charge

    • What observation was made regarding most alpha particles during Rutherford's experiment?

  • They passed straight through the foil. (correct)
  • They produced high-energy reactions.
  • They were absorbed by the foil.
  • They all deflected back to the source.

    • What was the unexpected outcome of Rutherford's experiments with alpha particles?

  • Most particles were absorbed by the foil.
  • Most particles passed through the foil. (correct)
  • All particles were deflected at the same angle.
  • Particles created new elements upon collision.

    • Which model of the atom did Rutherford's results challenge?

    <p>Thomson's model</p> Signup and view all the answers

    What did Rutherford predict about the size of the positive charge relative to the entire atom?

    <p>It is small in volume relative to the atom.</p> Signup and view all the answers

    What is one possible explanation for the deflection of alpha particles in Rutherford's experiment?

    <p>Concentrated positive charge at the atom's center.</p> Signup and view all the answers

    What percentage of alpha particles were reflected back toward the source in Rutherford's experiment?

    <p>A small fraction of particles</p> Signup and view all the answers

    What did the alpha particle bombardment of gold foil reveal about atomic structure?

    <p>Atoms are mostly empty space.</p> Signup and view all the answers

    What key idea do the quantum mechanical model and Heisenberg's uncertainty principle share?

    <p>The exact position or speed of an electron cannot be known at the same time.</p> Signup and view all the answers

    According to the quantum mechanical model, how are orbitals described?

    <p>As probability distributions representing electron locations.</p> Signup and view all the answers

    Who first proposed the idea that electrons possess both particle and wave characteristics?

    <p>Louis de Broglie</p> Signup and view all the answers

    What does the wave function represent in quantum mechanics?

    <p>The probability of finding an electron in a certain location.</p> Signup and view all the answers

    How can electrons move between different orbitals according to the quantum mechanical model?

    <p>By absorbing or emitting energy quanta.</p> Signup and view all the answers

    In which state does the single electron in a hydrogen atom typically reside?

    <p>Ground state low-energy orbital</p> Signup and view all the answers

    What aspect of the quantum mechanical model makes it a complex understanding of atomic structure?

    <p>It incorporates the uncertainty of electron positions.</p> Signup and view all the answers

    What does electron probability density indicate?

    <p>The area where the likelihood of finding an electron is highest.</p> Signup and view all the answers

    What major contribution did Antoine Lavoisier make in the late 1700s?

    <p>Gathered accurate quantitative measurements of chemical reactions</p> Signup and view all the answers

    According to John Dalton's atomic theory, what can be said about atoms of the same element?

    <p>They are identical in size, mass, and other properties</p> Signup and view all the answers

    What experimental evidence first supported the existence of the electron?

    <p>Experiments using cathode ray tubes</p> Signup and view all the answers

    What characteristic describes the cathode ray in J.J. Thomson's experiments?

    <p>It is negatively charged and starts from the negative electrode</p> Signup and view all the answers

    Which scientific development allowed for the precise measurement of mass and volume in experiments?

    <p>The development of specialized measuring instruments</p> Signup and view all the answers

    How has John Dalton's atomic theory been viewed over time?

    <p>It has largely proven to be accurate and enduring</p> Signup and view all the answers

    What did J.J. Thomson refer to the apparatus he used in his experiments?

    <p>Cathode ray tube</p> Signup and view all the answers

    What role did electrical discharges play in Thomson's experiments?

    <p>They allowed for the observation of cathode rays</p> Signup and view all the answers

    What type of particles did Thomson hypothesize was in the cathode ray based on his observations?

    <p>Negatively charged particles</p> Signup and view all the answers

    What happens to the cathode ray in the presence of a negative electrical field?

    <p>It is repelled by the negative pole</p> Signup and view all the answers

    Using which formula did Thomson determine the charge-to-mass ratio of an electron?

    <p>$e = 21.76 imes 10^8 C/g$</p> Signup and view all the answers

    In a cathode ray tube, which component is responsible for producing the visible ray under high voltage?

    <p>Electron beam</p> Signup and view all the answers

    What is the charge of the particles that compose the cathode ray according to Thomson’s hypothesis?

    <p>Negative charge</p> Signup and view all the answers

    What type of environment is required in a cathode ray tube for visualization of the cathode ray?

    <p>Partially evacuated</p> Signup and view all the answers

    What role does the metal electrode play in the cathode ray tube?

    <p>To create the electric field</p> Signup and view all the answers

    Why did Thomson measure the deflection of the beam of electrons in a magnetic field?

    <p>To calculate the charge-to-mass ratio</p> Signup and view all the answers

    What was one of Thomson's main goals in his cathode ray tube experiments?

    <p>To understand the structure of the atom</p> Signup and view all the answers

    Which model is often referred to as the 'blueberry muffin model'?

    <p>Thomson's model of the atom</p> Signup and view all the answers

    How did Thomson deduce that atoms must also contain a positive charge?

    <p>Because atoms are electrically neutral</p> Signup and view all the answers

    What did Robert Millikan use to determine the charge of an electron?

    <p>Charged oil drops</p> Signup and view all the answers

    What was the significance of the charge-to-mass ratio found by Thomson in Millikan's experiments?

    <p>It helped calculate the mass of an electron</p> Signup and view all the answers

    What did Millikan adjust to halt the fall of charged oil droplets?

    <p>The voltage across two charged plates</p> Signup and view all the answers

    What hypothesis did Thomson make about the structure of an atom?

    <p>Electrons are embedded in a cloud of positive charge.</p> Signup and view all the answers

    What was the calculated mass of an electron according to Millikan?

    <p>$9.11 imes 10^{-31}$ kg</p> Signup and view all the answers

    Study Notes

    Early Atomic Theory

    • Antoine Lavoisier and others conducted accurate quantitative measurements of chemical reactions in the late 1700s
    • John Dalton proposed the first modern atomic theory in the early 1800s, stating that elements consist of atoms, which cannot be created, destroyed, or divided, and that atoms of the same element have identical properties

    The Discovery of the Electron

    • J.J. Thomson conducted cathode ray tube experiments in the late 1800s, which provided evidence for the existence of the electron, a negatively charged subatomic particle
    • Thomson determined the charge-to-mass ratio of an electron
    • Thomson’s “blueberry muffin model” posited that atoms consist of a diffuse cloud of positive charge with negatively charged electrons embedded randomly

    Robert Millikan’s Oil Drop Experiment

    • Robert Millikan determined the charge of an electron using charged oil drops in the early 1900s
    • Millikan used the charge of the electron and the charge-to-mass ratio determined by Thomson to calculate the mass of the electron

    Rutherford’s Gold Foil Experiment

    • Ernest Rutherford conducted the gold foil experiment in the early 1900s
    • Rutherford bombarded thin gold foil with alpha particles
    • Rutherford observed that most of the alpha particles passed straight through the foil, while some were deflected at various angles, and others were reflected back toward the source
    • Rutherford concluded that the atom's positive charge is concentrated in a small, dense nucleus with negatively charged electrons orbiting around it
    • Rutherford's model suggested that the atom is mostly empty space.

    The Quantum Mechanical Model

    • The quantum mechanical model describes the electron as a standing wave that can occupy a series of orbitals.
    • Each orbital has a prescribed possible energy and spatial distribution.
    • Heisenberg's uncertainty principle states that it is impossible to know both the position and the speed of a particle simultaneously.
    • The ground state of a hydrogen atom is when its single electron resides in a low-energy orbital.
    • Electrons can move between orbitals by absorbing or emitting quanta of energy.
    • The location of electrons is given by a probability distribution.

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    Early Atomic Theories and the Origins of Quantum Theory (PDF)

    Description

    Explore the foundational concepts of atomic theory and the discovery of the electron through pivotal experiments by Lavoisier, Dalton, Thomson, and Millikan. This quiz covers key historical developments and experiments that shaped our understanding of atomic structure. Test your knowledge on the early theories and discoveries that defined modern chemistry.

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