5.1 Models of the Atom

• Rutherford’s planetary model could not explain the chemical properties of elements.
• Bohr proposed that electrons move only in specific circular paths, or orbits, around the nucleus.
• The quantum mechanical model determines the allowed energies an electron can have and how likely it is to be found in various locations around the nucleus.
• Each sublevel of a principal energy level corresponds to an orbital shape describing where the electron is likely to be found.

5.2 Electron Arrangement in Atoms

• Three rules—the aufbau principle, the Pauli exclusion principle, and Hund’s rule—tell you how to find the electron configurations of atoms.
• Some actual electron configurations differ from those assigned using the aufbau principle because half-filled levels are not as stable as filled levels, but they are more stable than other configurations.

5.3 Physics and the Quantum Mechanical Model

• The wavelength and frequency of light are inversely proportional to each other.
• When atoms absorb energy, electrons move into higher energy levels. These electrons then lose energy by emitting light when the electrons drop back to lower energy levels.
• The light emitted by an electron moving from a higher to a lower energy level has a frequency directly proportional to the energy change of the electron.
• Classical mechanics adequately describes the motions of bodies much larger than atoms, while quantum mechanics describes the motions of subatomic particles and atoms as waves.