Flame: A Phenomenon - ConnectStudy

Usually, we use the words “fire” and “flame” interchangeably. Technically speaking, fire is the state of combustion, which produces the visual part of burning: flame.

As a kid, I wondered if flame is a solid, a liquid, a gas, or a completely undiscovered state of matter. It turned out that rather than being a matter, flame is actually a phenomenon.

Background information

Atoms & electrons

Every matter is made up of atoms, which are the basic units of chemical elements and combine to form molecules. Collectively, these molecules create substances like water and your pencils.

Inside each neutral atom (zero charges), you can find protons and neutrons (except Hydrogen atoms) in the middle, forming the nucleus, with electrons orbiting the nucleus.

The protons have a positive charge, the electrons have a negative charge, and the neutrons have zero charges. Electrons determine the chemical properties and the color of the atom, which will be explained in the next section.

Source: [Structure of Atoms]. (n.d.) https://keystagewiki.com/index.php/Atom

Light

Unlike atoms, light has the properties of both particles and waves. On the one hand, all visible and invisible light are electromagnetic waves, where electric and magnetic waves oscillate perpendicular to each other. (Image 1)

The type of light is determined by the wavelength and frequency of the electromagnetic waves. A light that is visible to human eyes constitutes a small proportion of the light spectrum.

On the other hand, light can be described by elementary particles called photons. Photons are the smallest unit of electromagnetic radiation – energy transmitted by electromagnetic waves.

Image 1: And1mu. (2016) [plane linearly polarized wave]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:EM-Wave.gif

Image 2: [The Light Spectrum]. (n.d.) https://eyelighting.com/lighting-technology-education/general-lighting-basics/light-spectrum

Sources: (Phillips, M. and Fritzsche, . Hellmut (Invalid Date). electromagnetic radiation. Encyclopedia Britannica. https://www.britannica.com/science/electromagnetic-radiation)

Sources: (Puiu, T. (2021, January 28). What exactly is a photon? Definition, properties, facts. ZME Science. https://www.zmescience.com/science/what-is-photon-definition-04322/)

The Light of Flames

(Image 1) To understand why flame displays light in a “supernatural” shape, we need to understand how atoms, electrons, and light interact with each other. When electrons of an atom acquire additional energy from either photons or collision with other particles, they enter an excited state.

Image 1: *(Background: Atoms and Light Energy*. (n.d.). NASA. https://imagine.gsfc.nasa.gov/educators/lessons/xray_spectra/background-atoms.html）

Image 2: *(Background: Atoms and Light Energy*. (n.d.). NASA. https://imagine.gsfc.nasa.gov/educators/lessons/xray_spectra/background-atoms.html）

(Volchko, J. (2019b, June 28). Visible Light Spectrum: From a Lighting Manufacturer’s Perspective. Lumitex, LLC. https://www.lumitex.com/blog/visible-light-spectrum)

(Image 2) After a certain amount of time, the excited electrons return to their ground states, releasing photons with the same energy as absorbed, but with a different wavelength.

Thus, when oxidation – a chemical reaction that involves the loss of electron(s) by an atom, molecule, or ion – occurs, electrons of reactants and products absorb some of the energy released by the chemical reactions and enter the excited state. Eventually, as the electrons release the energy, visible light and color (wavelength of 400–700 nanometers) are emitted.

How do we see the colors of flame?

Different elemental atoms emit different colors because when they are hit by photon(s), they absorb different wavelengths of light. This means that the wavelengths of light different elements released are also different, creating colors such as red or yellow. As a result, we perceive a color that is complementary to the absorbed wavelength of light. For example, if a substance absorbs a wavelength of blue (435-480nm), we would see that matter as yellow.

(The Chemistry of Light & Color. (2021, January 7). Radiant Vision Systems. https://www.radiantvisionsystems.com/blog/chemistry-light-color)

The Shape of Flames

The general teardrop shape of a flame is caused by gravity. Cooler, denser air is pulled downwards and displaces rising hot air, and this flow of air and moving particles make flames have their shape. Therefore, instead of being a substance or matter, flames are constituted of rising particles emitting light from their unstable electrons. Interesting fact: flames are actually hollow on the inside, as there is no contact to oxygen from within.