Physics and the Quantum Model

Light The idea for the the quantum mechanical model grew out of the study of light Light consists of waves The amplitude of a a wave is the height from zero to crest Wavelength (λ) is the distance between crests Frequency (ν) is the number of wave cycles that pass a given point per unit of time Frequency is measured in hertz (Hz)

Light c= λν c is a constant, equal to 2.998 x 108 m/s, so frequency and wavelength are inversly proportional

Atomic Spectra Atoms can absorb energy that raises electrons into higher energy levels. The electrons then lose the energy by emitting light when electrons return to their lower energy level. The light emitted by electrons only contains certain wavelengths of light. Each frequency corresponds to a specific color Each element emits a unique atomic emission spectrum

Uses of Atomic Spectra

How it Works An electron has a lowest possible energy called it’s ground state. For hydrogen, its ground state is n=1 Absorbing energy can excite the electron to n=2,3,4,5 or 6 A quantum of energy in the form of light is emitted when an electron drops back to a lower energy level The light emitted by an electron transition from higher to lower is derectly proportional to the energy change in the electron, therefore each transition produces a line of a specific frequency in the spectrum

Quantum Mechanics Light has a dual wave/particle nature Particles of light are called photons Experiments showed that electrons also behaved like particles and waves This wave like nature is used in electron microscopes since electrons have a much smaller wavelength than visible light Quantum mechanics describes the motion of subatomic particles and atoms as waves

Heisenburg Uncertainty Principle It is impossible to know exactly both the velocity and position of a particle at the same time

Tying it Together The discovery of matter waves paved the way for Schrodinger’s quantum mechanical atom model. His theories include the wavelike motion of matter and the uncertainty principle.