Understanding Bohr's Atomic Model

• Bohr's Model furthers the evolution of understanding and models of atoms.

Problems with the Rutherford Model

• Rutherford's atomic model suggests electrons are in orbit around the nucleus in a system, like planets orbiting the Sun.
• The idea seemed reasonable since the Sun's gravity pulling planets is counteracted by planet movement. This is how electrons orbiting an atomic nucleus would behave
• Moving charged particles produce EM energy.
• Electrons traveling in orbit emits energy as photons and loses energy.
• If electrons lose energy as they orbit, they should spiral toward the nucleus, collapsing the atom.

Spectroscopy

• Robert Bunsen and Gustav Kirchhoff invented the spectroscope in 1859.
• Spectroscopy analyzes spectra, like visible light, UV, and X-rays.
• An emission spectrum forms when light passes through a spectroscope.
• Bright-line spectra are patterns of light.
• Continuous spectrum contains every wavelength in a region of the EM spectrum, such as white light passing through a prism.
• Emission spectrum appears when passing light from heated gas through a prism to separate the emitted light into its components.
• Each element has a unique line spectrum.
• Spectrometers are nifty tools to identify unknown elements.

Line Spectrum of Hydrogen

• Niels Bohr utilized spectroscopy techniques to develop a quantum model.
• The line spectrum of hydrogen shows the electron exists only at discrete energy levels AKA quantized energy
• Requires energy to move electrons from various states.
• Electrons have particular discrete energy levels.

Bohr's Postulates

• Bohr's model has two main postulates.
• Electrons do not radiate energy as they orbit around the nucleus with each orbit corresponding to a state of constant energy called its ground state.
• Electrons can only change their energy during transition from one stationary state to another, also known as an excited state.
• Electrons must absorb sufficient energy for this to happen.
• Electrons gain a photon to move to a higher energy level and lose a photon to move from higher to lower energy levels.
• A quantum of energy is released as a photon when an electron returns to its ground state.

Bright-Line Spectrum: Staircase Analogy

• The shells are concentric, circular, and converge meaning that they are not evenly spaced.
• Higher energy levels are more closely packed together.
• Electrons make jumps of varying distances, and not every line on the emission spectrum is evenly spaced.

Emission Spectrum: Line Colours

• Not all EM radiation is visible to the eye.
• Most electron transitions happen where energy is released to ground state in wavelengths beyond the human visible spectrum.

Successes and Failures of Bohr's Model

• Bohr's Model shows the filling of successive orbitals and predicts the number of electrons in all energy levels.
• The model explained that higher energy levels contain more energy.
• The model did not account for electron motion so it could not explain where or how electrons move.
• Spectra can only be explained for hydrogen, with calculated energy levels for electrons which are similar to values obtained from the emission spectrum.
• The data from atoms with multiple electrons did not match the predicted model.

Bohr's model advanced atomic understanding beyond Rutherford's. Rutherford's model faced issues as orbiting electrons should emit energy, spiral inward, and collapse the atom. Spectroscopy, with tools like the spectroscope, analyzes spectra, revealing emission patterns and continuous spectra.