Electromagnetic Spectrum and the Quantum Mechanical Model of the Atom
Recall that all light (both visible, and invisible parts of the EM spectrum) are waves that travel at the speed of light, which is the constant "c". Photons are massless and exhibit wave-particle duality, meaning they have properties of both waves (interference, etc.) and particles when in motion at "c". The equations of energy that relate frequency and wavelength apply to the EM spectrum. When excited (high-energy) electrons fall toward the nucleus, they lose energy and photons are emitted.
Valence Electrons, Electron Configurations, & Orbital Diagrams
How to Write Electron Configurations (includes Aufbau, Pauli Exclusion, and Hunds' Rules)