Bohr radius a₀ in terms of fundamental constants:

Answer: 4pi eps₀ hbar²/(m_e e²).

A hbar/(m_e c)
B 4pi eps₀ hbar²/(m_e e²)
C e²/(m_e c²)
D m_e e²/(4pi eps₀ hbar²)

Correct answer: B. 4pi eps₀ hbar²/(m_e e²)

Explanation: a₀ = (4pi eps₀ hbar²)/(m_e e²) = 0.529 Angstrom. It sets the scale of atomic orbitals.

Comparison of the Thomson model and the Rutherford model of the atom: in the Thomson plum pudding model alpha particles pass almost straight through a diffuse positive sphere, while in the Rutherford model a concentrated central nucleus deflects some alpha particles through large angles, with the lower panels showing the alpha particle source and gold foil and the observed result of wide-angle scattering

The Geiger–Marsden alpha-scattering result: a few alpha particles bounce back at large angles, which rules out Thomson’s diffuse model and demands a tiny, massive, positively charged nucleus. Image: Kurzon, CC BY 3.0, via Wikimedia Commons.

Concept context

Thomson's plum-pudding model, Rutherford's nuclear model from alpha-scattering, Bohr's postulates and hydrogen spectrum, spectral series (Lyman to Pfund), Rydberg formula, and limitations of each model.

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Bohr radius a₀ in terms of fundamental constants:

Concept context

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