Atomic Theories and Models Quiz

Dalton's Atomic Theory

• States that elements are composed of atoms, which are indivisible particles.
• Atoms of the same element are identical, while atoms of different elements have different properties.
• This theory served as a foundational concept for modern atomic theory.

Thomson's Atomic Model

• Described the atom as a positively charged sphere with negatively charged electrons embedded within it.
• The model was based on the idea that the atom is electrically neutral.
• This model was unable to explain certain observed phenomena, including the spectral series of hydrogen and the scattering of alpha particles.

Rutherford's Atomic Model

• Proposed based on experiments involving the scattering of alpha particles by thin gold foil.
• The model described the atom as consisting of a small, dense, positively charged nucleus at the center, with negatively charged electrons orbiting around it.
• The model explained the observed large-angle scattering of alpha particles.

Distance of Closest Approach

• This refers to the minimum distance an alpha particle comes to the nucleus before being deflected.
• The value depends on the alpha particle's kinetic energy and the nucleus's atomic number.

Impact Parameter

• The perpendicular distance between an alpha particle's velocity vector and the nucleus when the particle is far away.
• Determines the scattering angle of the alpha particle.

Rutherford's Scattering Formula

• Relates the number of alpha particles scattered at a specific angle to the impact parameter, atomic number, energy of the alpha particles, and thickness of the foil.

Limitations of Rutherford's Model

• It failed to explain the stability of atoms, as the model predicted that electrons would lose energy and spiral into the nucleus.
• It couldn't explain the line spectrum of elements.

Bohr's Atomic Model

• Proposed that electrons can only exist in specific, quantized orbits around the nucleus.
• The model introduced the idea of energy levels, where electrons can transition between orbits by absorbing or emitting photons of light.
• The angular momentum of an electron in an orbit is quantized, meaning it can only take on specific values.

Hydrogen Spectrum Series

• The hydrogen atom emits a unique set of spectral lines, which are characteristic of the element.
• There are several spectral series, including the Lyman, Balmer, Paschen, Brackett, and Pfund series.
• The series correspond to transitions of electrons between different energy levels.

Lyman Series

• Occurs when electrons transition from higher energy levels (n = 2, 3, 4...) to the ground state (n = 1).
• Emits ultraviolet radiation.

Balmer Series

• Occurs when electrons transition from higher energy levels (n = 3, 4, 5...) to the second energy level (n = 2).
• Emits visible light.