Atomic Structure and Discoveries Quiz

Discovery of Protons and Neutrons

• Modified cathode ray tubes enabled the identification of positive charges, termed canal rays.
• Millikan's experiments demonstrated that the charge (q) on oil droplets is an integral multiple of the elementary charge (e); q = n*e (where n = 1, 2, 3...).
• Canal rays are positively charged gaseous ions, their charge-to-mass ratio varies by gas type.
• The smallest positive ion identified is the proton, derived from hydrogen.
• Rutherford's model suggests stability is questionable under classical mechanics due to electron movement.

Drawbacks of Rutherford Model

• The Rutherford atomic model likens an atom to a miniature solar system, where electrons orbit a dense nucleus.
• The model neglects the electronic structure, particularly how electrons are distributed around the nucleus.
• Classical mechanics predicts instability since electrostatic attraction would lead to electrons spiraling into the nucleus.

Black Body Radiation

• Black body radiators emit radiation based solely on temperature, characterized by a maximum intensity at specific wavelengths.
• The intensity of radiation increases with temperature but decreases as wavelength shortens beyond a certain point.

Photoelectric Effect

• In 1887, Hertz discovered that exposing specific metals (like potassium, rubidium, cesium) to light emitted electrons, termed the photoelectric effect.
• A critical frequency (threshold frequency) is required for electron ejection; below this threshold, no electrons are emitted.
• Light of higher frequency can liberate electrons with measurable kinetic energy, governed by the equation: KE = (h*(ν - ν₀)) where ν₀ is the threshold frequency.

Emission and Absorption Spectra

• When substances absorb energy, they emit radiation, forming an emission spectrum.
• Excited atoms or molecules transition to lower energy states, releasing radiation at characteristic frequencies.

Angular Momentum in Electron Orbits

• Angular momentum (L) for an electron in circular motion around a nucleus is quantized and defined as: L = mevr (where v is linear velocity).
• Only certain orbits are permissible, associated with integer multiples of h/2π (Planck constant).
• The Bohr model sets fixed orbits (n = 1, 2, 3...) corresponding to principal quantum numbers, with the first radius at r₁ = 52.9 pm (a₀).

Test your knowledge on the discovery of protons and neutrons, along with the limitations of the Rutherford model. This quiz covers key experiments and concepts, such as canal rays and black body radiation. Evaluate your understanding of atomic structure and its implications in classical mechanics.