Atomic models Transitional Reasoning Download PDF

Questions

1. 1.

   In his cathode-ray experiments, J. J. Thomson measured the deflection of cathode rays in electric and magnetic fields and discovered that their charge-to-mass ratio remained constant regardless of the electrode material or residual gas used. Furthermore, the mass of each ray particle was determined to be orders of magnitude smaller than that of a hydrogen atom. Which direct deduction from these findings required scientists to replace John Dalton's billiard-ball model of the atom?

   • A) Atoms are divisible structures containing identical, negatively charged subatomic particles common to all elements.
   • B) Positive charge and atomic mass are concentrated in an extremely compact, central nucleus surrounded by empty space.
   • C) Electrons orbit in stable, non-radiating shells with discrete angular momentum values.
   • D) Neutral particles of comparable mass to protons reside alongside positive charges to stabilize the atomic core.
2. 2.

   A student reviewing historical atomic models notes that Rutherford's planetary model could not explain why accelerating orbiting electrons do not continuously radiate electromagnetic energy and spiral into the nucleus, nor could it explain the discrete line spectra emitted by excited gases. To resolve these contradictions, Niels Bohr introduced a revised model of the hydrogen atom. Which principle did Bohr postulate to account for both the mechanical stability of the atom and the observed discrete spectral lines?

   • A) Electrons are distributed evenly throughout a uniform sphere of positive charge, neutralizing acceleration forces.
   • B) Electrons have wave-particle duality and occupy three-dimensional probability density clouds described by orbital shapes.
   • C) Protons and neutrons combine in the nucleus to exert a strong nuclear force that directly counteracts electron radiation.
   • D) Electrons occupy stable, non-radiating stationary orbits and emit or absorb photons only when transitioning between these discrete energy levels.
3. 3.

   When alpha particles were directed at a thin gold foil to test Thomson's atomic model, the vast majority passed through undeflected, but approximately one in every few thousand was deflected by angles greater than 90°. Which fundamental conclusion about atomic structure was deduced from the observation that a few massive, positively charged particles bounced back almost directly toward their source?

   • A) Electrons move in discrete, quantized orbits where they do not emit electromagnetic radiation.
   • B) The positive charge and almost all of the atom's mass are concentrated in a tiny, dense central core, with the remaining volume being mostly empty space.
   • C) Atoms are solid, indivisible spheres of uniform density that combine in simple whole-number ratios.
   • D) Negative charges are uniformly distributed throughout a continuous, positively charged sphere of atomic dimensions.