Atoms

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According to Thomson's model (1898), the positive charge of an atom is uniformly distributed throughout its volume, with negatively charged electrons embedded in it like seeds in a watermelon. The ato

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Setup: 5.5 MeV α-particles from radioactive Bi-214 were directed at a thin gold foil (2.1×10⁻⁷ m thick). Scattered particles were detected using a zinc sulfide screen and microscope. Key observations:

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Rutherford's nuclear model states that: (1) The entire positive charge and most of the mass are concentrated in a tiny nucleus (10⁻¹⁵ to 10⁻¹⁴ m), (2) Electrons revolve around the nucleus in orbits li

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Two main problems: (1) Stability issue: According to classical electromagnetic theory, revolving electrons should continuously emit radiation, lose energy, and spiral into the nucleus, making atoms un

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Emission spectrum: When an atomic gas is excited (by electric current), it emits light containing only specific wavelengths, appearing as bright lines on a dark background. Absorption spectrum: When w

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1st Postulate: Electrons revolve in certain stable orbits (stationary states) without emitting radiation. 2nd Postulate: Angular momentum is quantized: L = nh/2π, where n = 1,2,3... (principal quantum

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For circular orbit: Centripetal force = Electrostatic force mv²/r = ke²/r² From quantization: mvr = nh/2π, so v = nh/2πmr Substituting: m(nh/2πmr)²/r = ke²/r² Simplifying: rn = (n²h²/4π²mke²) = n²(h²/

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The Bohr radius a₀ = h²/4π²mke² = 5.3×10⁻¹¹ m is the radius of the first orbit (n=1) in hydrogen atom. It represents the most probable distance of the electron from the nucleus in the ground state. Al