Presentation on theme: "Light Quantum Theory Max Planck (1900) – Observed - emission of light from hot objects – Concluded - energy is emitted in small, specific amounts (quanta)"— Presentation transcript:
Quantum Theory Max Planck (1900) – Observed - emission of light from hot objects – Concluded - energy is emitted in small, specific amounts (quanta) – Quantum - minimum amount of energy change Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem Max Planck
Continuous vs. Quantized Energy Energy A B Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 330 continuous quantized
Quantum Theory Planck (1900) vs. Classical Theory Quantum Theory Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Light Particles – photons (discrete bundles of energy) Light is emitted when electrons return to ground state from an excited state Waves – Frequency, wavelength Wave-Particle duality
Wave-Particle Duality JJ Thomson won the Nobel prize for describing the electron as a particle. His son, George Thomson won the Nobel prize for describing the wave-like nature of the electron. The electron is a particle ! The electron is an energy wave!
The Wave-like Electron Louis deBroglie The electron propagates through space as an energy wave. To understand the atom, one must understand the behavior of electromagnetic waves.
Formation of Light Nucleus e e Lithium Atom + Ground State e e Excited State e Electron Returns to Ground State Light is given off e Ion is formed Li e + Li 1+ hv n = 1 n = 2 n = 3 n = 4 n = 5 n = 6 n = 7 Nucleus
e-e- e-e- Ground state Excited state Electrons can only be at specific energy levels, NOT between levels.
Energy Level Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 329 A B CD Ground state Energy Four excited states
An Excited Lithium Atom Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 326 Photon of red light emitted Li atom in lower energy state Excited Li atom Energy
Humor Question: Why does hamburger have lower energy than steak? Answer: Because it’s in the ground state.
Visible Spectrum of Light PRISM Slit Ray of White Light Waves 1 / 33,000 ” long Waves 1 / 70,000 ” long R ed O range Y ellow G reen B lue I ndigo V iolet
The Electromagnetic Spectrum AM radio Short wave radio Television channels FM radio Radar Microwave Radio Waves Gamma Rays X- Raysinfrared Increasing photon energy Increasing frequency Decreasing wavelength Red Orange Yellow Green Blue Indigo Violet UV Rays VisibleLightVisibleLight R O Y G B I V HIGHENERGYHIGHENERGY LOWENERGYLOWENERGY
Prism White light is made up of all the colors of the visible spectrum. Passing it through a prism separates it. Author: Thomas V. Green Jr.
If the light is not white By heating a gas or with electricity we can get it to give off colors. Passing this light through a prism does something different. Author: Thomas V. Green Jr.
Atomic Spectrum Each element gives off its own characteristic colors. Can be used to identify the atom. How we know what stars are made of. Author: Thomas V. Green Jr.
Bohr Model electrons exist only in orbits with specific amounts of energy called energy levels Therefore… electrons can only gain or lose certain amounts of energy only certain photons are produced Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Bohr Model 1 2 3 4 5 6 Energy of photon depends on the difference in energy levels Bohr’s calculated energies matched the IR, visible, and UV lines for the H atom Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem nucleus
Other Elements Each element has a unique bright-line emission spectrum. i.e. “Atomic Fingerprint” Helium z Bohr’s calculations only worked for hydrogen! Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Hydrogen Spectral Lines A B C D E F Lyman series (UV) A B C D E Balmer (Visible) A B C D Paschen (IR) E1E1 E2E2 E3E3 E4E4 E5E5 E6E6 Energy Bohr’s model of the atom accounted mathematically for the energy of each of the transitions shown. IR region UV region 656 nm 486 nm 434 nm 410 nm Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 97 ionization
Emission Spectrum of Hydrogen 1 nm = 1 x 10 -9 m = “a billionth of a meter” 410 nm434 nm486 nm656 nm
Emission Spectrum of an Element 1 nm = 1 x 10 -9 m = “a billionth of a meter” 410 nm434 nm486 nm656 nm 1 nm = 1 x 10 -9 m = “a billionth of a meter”
Continuous and Line Spectra 4000 A o 5000 60007000 4000 A o 5000 6000 7000 light Na H Ca Hg
Flame Emission Spectra Photographs of flame tests of burning wooden splints soaked in different salts. methane gas wooden splintstrontium ioncopper ionsodium ion calcium ion