|MadSci Network: Physics|
Quantum refers to a finite amount. In the case of physics it is about the energy states of atoms and molecules. The atom is somewhat like the solar system, heavy mass in the center (sun, protons/neutrons) and light particles in orbit (planets, electrons). Unlike planets however, electrons can not just orbit anywhere. Their energy states or levels are divided up and electrons must take finite steps to move from one to another. Absorbing a photon of a certain energy to reach a higher energy state, emitting one to go down to a lower state. It is analogous to traveling up and down stairs (you can't go part way up 1 stair). For a simple review of atomic spectroscopy (from an astronomical point of view) visit my physical science class lecture pages on spectra especially the slide on Emission Spectra This should help your understanding greatly.
When you spray a chemical into the flame, be it potassium chloride, strontium nitrate, or a single element, the heat from the flame will excite electrons in the atoms to higher energy states. When those electrons de-excite they will emit photons with a particular energy. Not just any energy. An energy equal to an atomic transition (step) in the atom. (E = h f) Energy, planck's constant, and frequency.
The flame color test is a sort of simple extremely low resolution spectroscopy experiment. Although there may be several energy transitions (photons) emitted corresponding to several energy states in the atom, their integrated light combine to give you the single color in the flame much as a chord on the piano is one sound from many different notes.
Various chemicals are used in industry, especially pyrotechnics on July 4th, to create the beautiful fireworks displays.
Strontium Nitrate = Yellow Strontium Chloride = Reds Barium Chloride = Greens Copper, Cobalt = Blues etc.
Try the links in the MadSci Library for more information on Physics.