Solution

The bright, colorful part of the fireworks display is caused by “excited” electrons in the atoms of different metal and salt compounds. These compounds are in little balls called stars, made of a similar compound to what makes a sparkler work. Different metals burn in different colors. For example, if a copper compound is lit, its flame will be a blue-green color. Calcium burns red-colored and potassium burns purple. In fireworks, metals are combined to create different colors.

When the star compounds inside a firework are heated, the excited atoms give off light energy. This light falls into two categories: incandescence and luminescence.

• Incandescence is light produced from heat. In fireworks, reactive metals (aluminum or magnesium) cause a burst of very bright light — sometimes at temperatures over 5000° F! Compounds that are less reactive don’t get as hot, resulting in dimmer sparks.

• Luminescence, on the other hand, is produced from other sources and can occur even at cold temperatures.

The electrons in the compound absorb energy, making them “excited.” The electrons can’t maintain this high level, though, so they jump back to a lower level. They release light energy (photons) in the process. Barium chloride gives fireworks a luminescent green color, and copper chloride makes a blue color. For either kind of light, it’s important to use pure ingredients since traces of other compounds will obscure the color.