posted by Sarah .
We did a flame test today to see what substances produce what colors when burned.
Can you please explain...
Why each of the different elements have a different atomic emission spectrum?
Would the flame tests be useful for detecting individual elements present in a mixture of elements?
Atoms usually exist in their "so-called" ground state; i.e., the lowest energy. When an atom is placed in a flame, the energy from the flame is enough to make an outer electron (say from a Na atom) move from the 3s level to a higher energy level. After a short period of time the electron falls back to its initial 3s level. When it does that it releases the same amount of energy it absorbed in the first place. For the Na atom that energy is in the yellow part of the spectrum and that's the color one sees with Na. For other atoms the color is different because it takes a different amount of energy to move an outer electron of K than it does for Na. In fact, no two elements have the same spectrum because each element moves different electrons to and from different energy levels.
Flame tests are extremely helpful in identifying SOME (but not all) elements. Ba, Na, K, Sr, Li, Cu, Ni, and a few others have characteristic flame emission spectra. The spectrum of some elements interferes with the spectrum of other elements; e.g., K can not be detected in the presence of Na without a special technique.