Modern Chemistry Flashcards
Velocity of Light
C = λf
C=3.00 x 10^8 m/s
Visible light spectrum
Infrared - Visible Light - Ultraviolet
V.L. = 700nm-400nm (ROYGBIV)
Frequency
f (Hertz) = # events / time(sec)
Black Body Radiation
When solids are heated they emit radiation
Max Planck (1858-1947)
Challenges continuous model of energy (waves).
Proposed electromagnetic radiation is emitted in tiny packets of energy called quanta. A quanta of visible radiation is a photon. Energy of a quanta is proportional to it’s frequency.
Discontinuous Model
Planck’s Equation
E = hf
h is 6.63 x 10^-34 J sec
Photoelectric Effect
Shining light on a metal surface emits electrons.
Electrons are emitted if frequency of light is high enough.
If low frequency, no electrons are emitted regardless of intensity or brightness.
Albert Einstein’s explanation of the Photoelectric Effect
High-energy photon collides w/ an atom & causes it to lose an electron.
Electron can only be torn away w/ some minimum amount of energy.
If photon doesn’t have that threshold amount of energy, no electron will be emitted regardless of how many photons collide.
Bright-Line Spectrum (Emission Spectra)
If high voltage is applied to atoms/elements in gas phase, they absorb energy & are “excited”.
They emit light.
When viewed through a spectroscope or passes through a prism distinct bands of color are observed rather than a continuous spectrum.
Niels Bohr (1885-1962)
Attempts to explain emission of light from an atom w/ Planetary Model developed by Rutherford.
Assumed classic mechanics would not explain the emission spectrum.
Bohr’s Model of Hydrogen Atom
Proposed electrons or orbited nucleus in circular pathways.
Only orbits of certain radii corresponding to definite energies are permitted.
Louis de Broglie (1892-1987)
Proposed that all matter has particle & wave natures.
The “wave” is observed for very low mass, high velocity materials.
Werner Heisenberg (1901-1976)
Uncertainty Principle
-Impossible to know exact momentum & location of an object in motion.
Electrons can’t be modeled moving in well defined orbits.
Only probability of locating an electron in a specific region of space is possible.
Erwin Schrodinger (1887-1961)
Treated electron as wave.
Developed equation to give location of electrons in an atom. Used probability to describe electron orbitals.
Orbitals visualized as clouds where electrons are most likely to be found.
