5.3 Physics and the Quantum Mechanical Model QMM grew out of a study of light 1666 Newton said light consists of particles

Light By 1900, there’s enough experimental evidence to convince scientists that light consists of waves

Wavelength (λ, Greek symbol Lambda) Measured in m or nm Frequency (ν, Greek symbol nu) # waves per unit of time Measured in cycles per second SI unit = hertz (Hz) Reciprocal second, s-1 (1/s) Amplitude = height from zero to crest

C = νλ Frequency and wavelength are inversely proportional to each other All electromagnetic waves travel in a vacuum at a speed of c = 2.998 x 108 m/s

Calculate the wavelength of the yellow light emitted by sodium lamp if the frequency of the radiation is 5 x 1014 Hz.

Electromagnetic Spectrum

Electromagnetic Spectrum Wave model  light is made up of electromagnetic waves Visible light ranges from red (low energy, 700 nm) to violet (high energy, 380 nm)

Atomic Spectra Atoms absorb energy, e- move to higher energy levels. e- lose energy by giving off light as they return to lower energy levels Light emitted by atoms is a mixture of specific frequencies, each frequency corresponds to a certain color Emission spectrum

Emission spectrum of an element is like a fingerprint, no two elements have the same Used to identify elements

Lowest possible energy of electron is its Ground State Absorbs energy and moves to EXCITED STATE Quantum of energy (light) emitted when electron drops back to lower energy level Emission takes place in an abrupt step called electronic transition

> Frequency >Energy Energy and Frequency Photon - A quantum of light (packet of energy) The light emitted has a frequency directly proportional to energy change of electron > Frequency >Energy

Energy per photon ∆E = hc/λ ∆E = hν h = 6.626 x 10-34 J ∙ s/photon (h = Planck’s constant)

Hydrogen Spectrum

Lyman series- transition to n = 1 (ultraviolet) Balmer series- transition to n = 2 (visible) Paschen series- transition to n = 3 (infrared)

Quantum Mechanics De Broglie predicted that all moving objects have wavelike behavior Classical mechanics describes the motions of bodies much larger than atoms Quantum mechanics describes the motions of subatomic particles and atoms as waves

Heisenberg uncertainty principle-it is impossible to know exactly both the velocity and the position of a particle at the same time