Atomic Structure and Models
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Which statement best describes Thomson's model of the atom?

  • Atoms consist of a central nucleus surrounded by electrons.
  • Atoms are made up entirely of positively charged protons.
  • Atoms are solid spheres with no internal structure.
  • Atoms contain positively charged spheres with electrons embedded within. (correct)

    • What was a major limitation of Thomson's model of the atom?

  • It proposed that electrons were stationary.
  • It failed to account for the presence of neutrons.
  • It incorrectly described the size of the nucleus.
  • It could not explain the spectral lines of hydrogen. (correct)

    • What significant discovery did Rutherford's alpha-ray scattering experiment lead to?

  • The concept of electron orbits around atoms.
  • The discovery of electrons being negatively charged.
  • The construction of atomic models using protons and neutrons.
  • The presence of the atomic nucleus. (correct)

    • How does the size of the atomic nucleus compare to the size of the atom?

    <p>The nucleus is much smaller than the atom by a factor of $10^5$.</p> Signup and view all the answers

    What is the total charge of an alpha particle?

    <p>2 positive charges.</p> Signup and view all the answers

    At the distance of closest approach, what happens to the kinetic energy of an alpha particle?

    <p>It reduces to zero.</p> Signup and view all the answers

    Which of the following equations represents the relationship between kinetic energy and electric potential energy at the distance of closest approach?

    <p>$KE = PE$ implies $ rac{1}{2} mv^2 = rac{1}{4 rac{ ext{pi}}{ ext{epsilon}_0}} rac{(ze)(2e)}{r_0}$.</p> Signup and view all the answers

    In Rutherford's model, what provides the necessary centripetal force for electrons to revolve around the nucleus?

    <p>Electrostatic force of attraction.</p> Signup and view all the answers

    What is the equation that relates the energy difference between two states to the frequency of emitted radiation?

    <p>$E_2 - E_1 = hv$</p> Signup and view all the answers

    In which spectral series do the transitions occur from any higher energy state to the ground state in the hydrogen atom?

    <p>Lyman Series</p> Signup and view all the answers

    Which of the following spectral series contains lines in the visible region?

    <p>Balmer Series</p> Signup and view all the answers

    What is the Rydberg formula used for?

    <p>Calculating the wavelength of emitted light</p> Signup and view all the answers

    In the hydrogen atom, what is the value of Z?

    <p>1</p> Signup and view all the answers

    What does the wave number represent in the context of the spectral lines?

    <p>Number of complete waves in unit length</p> Signup and view all the answers

    Which series involves transitions to the third orbit in hydrogen?

    <p>Paschen Series</p> Signup and view all the answers

    What is represented by an energy level diagram?

    <p>The energies of electrons in different stationary orbits</p> Signup and view all the answers

    What does the impact parameter measure in relation to an alpha particle?

    <p>The perpendicular distance of the particle's velocity vector from the nucleus</p> Signup and view all the answers

    According to the limitations of Rutherford's atom model, what is a consequence of electrons emitting energy?

    <p>There should be a continuous emission of electromagnetic radiation</p> Signup and view all the answers

    What is the expression for the radius of the stationary orbit of an electron in a hydrogen atom?

    <p>r = n^2 h^2 / (4 imes rac{ heta^2}{2} mk e^2)</p> Signup and view all the answers

    In Bohr's model of the hydrogen atom, what is the significance of the quantization of angular momentum?

    <p>It defines specific allowed radii for electron orbits in the atom</p> Signup and view all the answers

    What determines the energy difference when an electron transitions between stationary orbits in Bohr's model?

    <p>The difference in total energy of the electron in different orbits</p> Signup and view all the answers

    What can be concluded about the total energy of an electron in a stationary orbit?

    <p>Total energy is negative, indicating the electron is bound to the nucleus.</p> Signup and view all the answers

    How does the orbital velocity of an electron in outer orbits compare to that in inner orbits?

    <p>Orbital velocity is smaller in outer orbits compared to inner orbits.</p> Signup and view all the answers

    How does Bohr's model describe the forces acting on the electron in its orbit?

    <p>The centripetal force required is provided by electrostatic forces</p> Signup and view all the answers

    What is the ionization energy for a hydrogen atom?

    <p>13.6 eV</p> Signup and view all the answers

    What defines a 'stationary orbit' as per Bohr's postulates?

    <p>An orbit in which the electron does not lose energy or radiation</p> Signup and view all the answers

    The frequency of an electron in a stationary orbit is determined by which of the following equations?

    <p>f = 2 heta kze^2 / nh</p> Signup and view all the answers

    What role does Planck's constant play in Bohr's model?

    <p>It defines the relationship between energy differences and frequency of radiation</p> Signup and view all the answers

    Which of the following represents the relationship between kinetic energy and potential energy in a stationary orbit?

    <p>KE = -PE</p> Signup and view all the answers

    What is the mathematical expression for the centripetal force acting on an electron in a hydrogen atom according to Bohr's model?

    <p>$F = rac{mv^2}{r}$</p> Signup and view all the answers

    What does the Rydberg formula describe within the context of atomic energy levels?

    <p>The energy transitions between various atomic orbits.</p> Signup and view all the answers

    Which statement is true regarding the energy of an electron in higher orbits?

    <p>Energy values are progressively smaller (less negative) in higher orbits.</p> Signup and view all the answers

    What is the energy of the electron in the second orbit of a hydrogen atom?

    <p>-3.4 ev</p> Signup and view all the answers

    At what energy level does an electron in a hydrogen atom achieve ionization?

    <p>0 ev</p> Signup and view all the answers

    According to Bohr's second postulate, what is quantized in the model of the hydrogen atom?

    <p>Angular momentum</p> Signup and view all the answers

    Which of the following correctly represents the relationship for permissible orbits in the hydrogen atom?

    <p>$2\pi r_n = n\lambda$</p> Signup and view all the answers

    What happens when an electron absorbs energy and jumps to a higher energy level?

    <p>It becomes excited</p> Signup and view all the answers

    How does the energy of an electron change as it moves to higher orbits in a hydrogen atom?

    <p>It increases without bound</p> Signup and view all the answers

    Which limitation is NOT associated with Bohr's theory of the hydrogen atom?

    <p>It describes elliptical orbits accurately</p> Signup and view all the answers

    What is the de Broglie wavelength associated with an electron in the nth orbit?

    <p>$\lambda = h/mv_n$</p> Signup and view all the answers

    Study Notes

    Atomic Structure

    • Dalton postulated that matter is made of atoms
    • Thomson proposed a model of the atom: positively charged spheres with electrons embedded within
    • Rutherford's experiment (using alpha particles and gold foil) discovered the atomic nucleus
    • The nucleus is small, dense, and positively charged, containing almost all the atom's mass
    • Protons and neutrons (in the nucleus) have approximately the same mass; protons have a positive charge and neutrons no charge.
    • Electrons are negatively charged and orbit the nucleus (e-).
    • The number of protons defines the atomic number of the element

    Thomson's Atomic Model

    • Positively charged sphere containing negatively charged electrons
    • Electrons are embedded throughout like plums in a pudding.
    • The atom is electrically neutral (equal positive and negative charges)

    Rutherford's Atomic Model

    • Experiment involved firing alpha particles at a gold foil
    • Most alpha particles passed straight through the foil
    • Some particles were deflected significantly, indicating a small but dense positive nucleus at the center of the atom
    • Nucleus contains most of the atom's mass

    Limitations of Thomson's Model

    • Could not explain the scattering of alpha particles
    • Could not explain the line spectrum of hydrogen

    Rutherford's Experiment - Observations

    • Most alpha particles pass straight through
    • Some alpha particles are deflected at large angles
    • A few alpha particles are reflected back

    Rutherford's Experiment - Conclusions

    • Atom has a tiny, dense, positive nucleus at the center
    • Electrons orbit the nucleus

    Rutherford's Atomic Model - Limitations

    • Could not explain the stability of the atom (electrons losing energy and spiralling into the nucleus)
    • Could not explain the line spectra of atoms

    Bohr's Model of the Atom

    • Electrons orbit the nucleus in specific, quantized energy levels
    • Electrons can only exist in these specific orbits and do not continuously emit energy
    • When an electron moves from one energy level to another, it absorbs or emits energy in the form of a photon
    • Electrons do not spiral into the nucleus due to the quantized nature of their energy levels
    • Angular momentum is quantized, which stabilizes the atom

    Bohr's Postulates

    • Electrons revolve in stable orbits without radiating energy
    • Electrons can only exist in certain specific energy levels
    • Emission and absorption of energy occur when the electron jumps between these energy levels
    • Quantized angular momentum of electrons restricts possible orbits

    Bohr's Explanation of Spectral Lines in Hydrogen

    • Electrons can jump between energy levels, emitting or absorbing photons
    • The frequency of the emitted or absorbed light corresponds to the energy difference between the energy levels
    • Different spectral lines correspond to different electron transitions.

    Limitations of Bohr's Model

    • Applicable only for the simplest atoms (e.g., hydrogen)
    • Does not account for the fine structure of spectral lines
    • Does not explain the behaviour of multi-electron atoms

    Atomic Spectra

    • Line absorption spectra: dark lines on a bright background, indicating specific wavelengths of light being absorbed
    • Line emission spectra: bright lines on a dark background, indicating specific wavelengths of light being emitted

    Energy Level Diagram

    • Diagram showing the energy levels of an atom's electrons
    • The energy levels are quantized
    • Transitions between energy levels correspond to specific frequencies of emitted or absorbed light.
    • Ionization energy: energy required to remove an electron from the outermost orbit

    de Broglie's Explanation

    • Electrons have wave-like properties
    • The electron orbit must have an integral number of de Broglie waves in it.

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    Atoms PDF

    Description

    Explore the foundational concepts of atomic structure, including the theories proposed by Dalton, Thomson, and Rutherford. Understand the key components of atoms, such as protons, neutrons, and electrons, as well as their charges and roles within the nucleus. This quiz will test your knowledge of early atomic models and their significance in chemistry.

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