Physics and the Quantum Mechanical Model

1. Physics and the Quantum Mechanical Model

2. Light (Waves) • Amplitude – The waves height from zero to the crest • Wavelength (λ) – The distance between two crests. • Frequency (ν) – The number of waves that pass a given point per unit time. Usually expressed in Hertz (Hz), cycles per second (s-1).

3. Light Waves (Continued) • c = λ ν The product of frequency and wavelength always equals a constant (c), the speed of light (2.998 x 108 m/s) What type of relationship does wavelength and frequency have? (hint: linear, inverse, or quadratic) Inverse. If we rearrange the formula to solve for wavelength, we get the following equation: λ = c / ν What happens to wavelength as frequency increases? Wavelength decreases

4. Sample Problem • What is the wavelength of radiation with a frequency of 1.50 X 1013 Hz? Does this radiation have a longer or shorter wavelength than red light? (Red light λ = 10-6) λ = c / ν λ = 2.998 X 108 m/s / 1.50 X 1013 Hz λ = 2.0 X 10-5 m The radiation has a longer wavelength than red light.

5. Light Waves (Continued) • Light consists of electromagnetic waves • Names a few types of electromagnetic radiation: • Radio waves, microwaves, infrared waves, visible light, ultraviolet waves. X-rays, and gamma rays. • All electromagnetic waves travel in a vacuum at a speed of2.998 X 108 m/s  speed of light

6. Light Waves (Continued) • What happens when sunlight passes through a prism? • Different frequencies separate into a spectrum of colors. (Atomic emission spectrum) • Name a natural phenomenon where light get separated into its constituent spectrum of colors. • A rainbow

7. Atomic Spectra • Passing an electric current through a gas in a neon tube energizes the electrons of the atoms of gas, and causes them to emit light. • When atoms absorb energy, electrons move to higher energy levels, and these electrons lose energy by emitting light when they return to lower energy levels.

8. Atomic Spectra Explanation • Ground state - The lowest possible energy level of an electron. Here the principal quantum number (n) is 1. • Excitation of an electron raises it from the ground state to an excited state (n) = 2,3,4,5,etc… • The light emitted by the electron moving from a higher to a lower energy level has a frequency directly proportional to the energy of the electron

9. Quantum Mechanics • Describes the motions of subatomic particles and atoms as waves. • Light quanta – Photon • Heisenberg uncertainty principal – It is impossible to know exactly both the velocity and the position of a particle at the same time.