I was listening to NPR Science Friday yesterday and Alan Alda was the feature guest.  He was describing his current work Visiting Professor and as a founding member of the Center for Communicating Science at Stony Brook University.  He set up a challenge were a scientist has to explain to an 11-year old what a flame is.  Below is my submission to the Flame Challenge.  I have had this question from students before but they are a little older so I simplified it somewhat.  Does this make any sense to anyone?  Eleven or not?


Fire, or a flame, is a plasma, that is, the fourth type of matter.  All matter starts out as a solid when it is cold enough (ICE).  In a solid particles are in a fixed position and touching each other.  If you increase the energy, the matter can be in liquid form where particles are moving but still in contact with each other (WATER).  Adding more energy, matter converts to a gas where particles moving and are not in touching each other (AIR).  Finally adding even more energy, matter converts to a plasma  where some electrons normally bound to an atom are freed so you have a mass of free electrons and atoms with missing electrons zooming around (FIRE).

Fire is produced as a result of a type chemical reaction known as combustion.  Combustion occurs when compounds combine with oxygen to form new compounds.  Most commonly, combustion occurs when hydrocarbons (compounds containing carbon and hydrogen, GASOLINE) and oxygen react and produce carbon dioxide and water.  In order to turn on the combustion reaction, activation energy (MATCHES) must be added to the system.  Once it is on, heat and light are produced and it continues until one of the reactants is used up or removed.  

During the reaction, enough energy is produced to free some of the electrons from atoms.  However, these free electrons and atoms with missing electrons are not happy being apart and quickly combine to form new compounds.  They form new compounds because matter wants to be stable and carbon dioxide and water are more stable than oxygen and gasoline.

Now the tough part:
Electrons are located in regions surrounding the central portion (the nucleus) of the atom.  These regions, also known as shells or energy levels, represent an approximate distance away from the nucleus of the atom.  The higher the shell, the higher the number.  Each shell can hold only a certain number of electrons so when a shell is full, the remaining electrons have to go to a higher level (THINK OF A LADDER).  When electrons are knocked out of their shell they are said to be excited (THINK OF THEM BEING AT A PARTY).  Electrons poop out pretty quickly and want to go back to their place in shell of an atom (HOME TO BED).  When electrons go back down to the lower shells of an atom, they give off light.