You just got finished with your 20 “Nuggets” of knowledge about people who helped shape atomic theory… We will go back and talk about the early days of atomic theory soon. Today, let’s focus on the development of atomic theory in the 1900s and WAVE MECHANICS.

In the late 1800’s, scientists noticed that objects glowed at certain colors when heated to high temperatures… Low temps  Warmer  Higher temps Even hotter Infrared Yellow glow White glow Bluish glow (not visible) (molten metal) (light bulb)

Waves and Light Notes Add a new scientist to your list: Scientist #21: 1900 Max Plank – Studied the relationship between heat and the color of light that an object gave off. He noticed that only certain colors were produced. -- Classical physics could not explain it.

Max Plank Conclusion: Energy does not exist as a continuous stream. Energy exists in small, discrete, definite packets of energy called quanta (1 quantum = 1 “chunk” of energy) This is the beginning of quantum mechanics! Energy = Plank’s Constant (h) x frequency E = h∙√ h = 6.626 x 10-34 Joule-sec √ = frequency in 1/sec or Hertz

Scientist 22 1905 Albert Einstein Was doing an experiment with light “sometimes” causing a piece of cesium or sodium metal to produce an electric current. Conclusion: The energy of the light had to be at a particular level in order for an electron to be released. (All or None). The “Photoelectric Effect”

Albert Einstein Won a Nobel Prize in Physics for his work on the photoelectric effect. Discovered a relationship between: electrons, light, frequency, energy, and electricity. Remember E = h∙√ If frequency is high, then energy of light is high. Discovered that light also acts like it is a particle: photons. This supported Plank’s quantum theory of light.

Group of Scientists for #23 Johann Balmer Theodore (Teddy) Lyman Fredrick Paschen These three studied light as it was given off by hydrogen atoms that were heated. The light contains a pattern of light called an Atomic Emission Spectrum or Bright Line Spectrum.

Emission Spectra The pattern for Helium is below. A non-colored pattern for Hydrogen is below and at the bottom of page 143 in text.

Waves A wave is a method of transmitting energy through a medium. There are two types of waves Longitudinal waves Transverse waves

Longitudinal Waves Examples: sound, slinky, traffic

Transverse Waves Examples: water, light, sine

General Properties of Waves Amplitude – a measure of the intensity of the wave For sound, amplitude is volume For light, amplitude is brightness Wavelength λ (lambda) – the distance between one part of a wave and the exact same part on the next wave Units can be miles, feet, yards, meters, cm, km, nm, Angstroms (1 x 1010 Å = 1 m)

General Properties of Waves Frequency – √ (nu) – the number of waves generated in a specific amount of time For sound, frequency is pitch For light, frequency is color or type of energy Units are in /sec, sec-1, waves/sec, cycles/sec, Hertz (Hz)

Speed c = λ∙√ λ=c/√ √ =c/λ In general, speed = distance/time For any wave, there is another formula for speed Speed = wavelength x frequency For a light wave, the product of frequency and wavelength always equals a constant (c), the speed of light c = λ∙√ λ=c/√ √ =c/λ

The Speed of Light (use the one to match your units!) 186,000 miles/sec 3.00 x 108 m/sec = 300,000,000 m/s 3.00 x 1010 cm/sec = 30,000,000,000 cm/s 3.00 x 1017 nm/s 3.00 x 1018 Å/sec

Relationships between variables As the wavelength of light increases, its frequency decreases As the frequency of light increases, its wavelength decreases As the frequency of light increases, the energy increases

The Electromagnetic Spectrum Light is just one kind of Electromagnetic Radiation. Electromagnetic Radiation includes these kinds of waves: radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays.

Electromagnetic Waves All of these are forms of energy. All of these travel in transverse waves. All of these travel at the same speed…. THE SPEED OF LIGHT (c)

Louis de Broglie #25 Asked the question: If waves can have particle properties, can particles have wave properties? He proposed that ALL MATTER could be viewed as having wave properties: electrons, protons, atoms, marbles, elephants, humans! de Broglie wavelength = Plank’s constant momentum  = h (we will come back to mv this later)

Scientist #24 1912-1914 Niels Bohr (Draw the picture that is on the board)

Atomic Spectra Passing electric current through a gas in a neon tube energizes the electrons of the atoms of the gas and causes them to emit light.

Atomic Spectra When atoms absorb energy, electrons move into an excited state. These electrons then lose energy by emitting a photon when they return to lower energy levels.

Atomic Spectra Each specific frequency of visible light emitted corresponds to a particular color. Each specific element has a unique emission spectrum that consists of discrete lines. No two elements have the same emission spectrum, so it is kind of like a fingerprint for that element! This is the fingerprint for Mercury!

Atomic Spectra Much of our knowledge of the composition of the universe comes from studying the atomic spectra of stars, which are hot glowing bodies of gases.

Three Differences Between Ground State and Excited State Electrons Ground State electrons…are closer to the nucleus than excited state electrons. Ground State electrons…have less energy than excited state electrons. Ground State electrons…are more stable than excited state electrons.

Why could electrons only exist in certain orbits? No one could explain why until de Broglie (1924). De Broglie saw a connection between his theory of wave characteristics of matter and the stable orbits of the Bohr model. An orbit was only stable if it contained an integral (whole) number of electron wavelengths! 1st orbit: 1 2nd orbit: 2  3rd orbit: 3 