Can you explain in some detail why different metal ions
emit various colors in a flame tests??
Atoms have specific energy levels that their atoms can exist at. Different
ions have different energy levels. When an material is heated, some of the
electrons absorb energy. This pops them to higher energy levels. When an
electron drops back down to a lower level, it releases the energy as
radiation. When the energy is high enough, we see it as light. Blue is the
highest energy visible light, while red is the lowest. Because each atom
has its own energy levels, it can only release specific colors of light.
Metal ions at room temperature are almost exclusively in their lowest
electronic state. When you heat the salt in a flame, the temperature is high
enough to 1. Evaporate some of the salt and 2. There is enough heat energy
to excite one or more (usually one) electron to a higher energy state. When
these atoms de-excite the energy in the form of light is emitted. Every
element has a characteristic fingerprint of emission lines depending upon
its electronic state.
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Update: June 2012