ASK A SCIENTIST
Question: When you see fire, what are the flames actually made out of and how does it work?
When you see a fire you are seeing chemical energy being released as visible light. All matter is made of chemicals. If the conditions are right, different chemicals can react. This means that their individual atoms combine in different ways to make other substances. When this happens, energy stored in the bonds that hold atoms together is either released or taken in. Some reactions require you to add energy while others give off energy.
All matter is composed of very small particles called atoms. In nature there are about 90 different atoms that combine in different ways to make all of the substances on earth. A particle made of atoms bonded together is called a molecule. Atoms have a small positive center called the nucleus, which is surrounded by a cloud of electrons that have a negative charge.
Examples of reactions that give off enough energy to make a flame include the burning of substances like natural gas, gasoline, and wood. The burning substance reacts with oxygen in the air to produce carbon dioxide and water as energy is released. In some cases the energy released just warms things up as it makes the molecules move faster. If enough energy is released it can cause electrons to move farther away from the center of their atoms. When the electrons fall back to their original orbits, also called energy levels, they give off weightless particles called photons which give us electromagnetic radiation. Some of these photons have energy that puts them in the visible light part of this energy spectrum. Other photons give us x-rays, ultraviolet rays, microwaves, and radio waves.
Flames are composed of hot gas molecules, products of a chemical reaction. Hot molecules in the flame are less dense than the surrounding air, which causes them to rise. This movement causes the flame to flicker and the light in the flame results as excited electrons in the hot gas fall back to lower orbits. The color of the light depends on how far the electrons fall. Each photon in our rainbow of visible light has its own quantity of energy. As you go from red to violet the photons have more and more energy. Each type of atom gives off it own colors of light which is how we can tell which atoms are in a flame or on a distant star.
Ask a Scientist appears Thursdays. Questions are answered by faculty at Binghamton University. Teachers in the greater Binghamton area who wish to participate in the program are asked to write to Ask A Scientist, c/o Binghamton University, Office of Communications and Marketing, PO Box 6000, Binghamton, NY 13902-6000 or e-mail firstname.lastname@example.org. Check out the Ask a Scientist Web site at askascientist.binghamton.edu. To submit a question, download the submission form(.pdf, 460kb).