HISTORY • Writings from 850 AD show that the Chinese used black powder to create “fireworks”. • People learned to encase black powder, making flares and missiles that would frighten invaders. • By the 12th century fireworks had become a part of religious ceremonies and many celebrations.
PYROTECHNICS(the art and science of artificial fire) • Fireworks must contain: -an oxidizer which provides oxygen for combustion -a fuel that acts as reducing agent • Oxidizers are electron deficient and so react with the fuel to increase their stability. This is an exothermic process; the energy that is released offers a spectacular show.
COLOUR • The colour of light we see depends upon the wavelengths of the electromagnetic radiation. • The visible spectrum contains red, orange, yellow, green, blue, and violet. Low-energy, longer wavelengths are at the red end of the spectrum and High-energy, shorter ones are at the violet end. • All colours together produce white light.
LIGHT • Light is emitted by: • Incandescence • Atomic Emissions • Molecular Emissions
Incandescence This kind of light is also known as white light . • Incandescent light is created when solid materials are heated to high temperatures, thus creating light. • Explosions with gold or white colours often result from reacting metal shavings in a high temperature environment.
Atomic & Molecular emissions These emissions create brilliant colour bursts. • Atomic Emissions: When light is emitted by atoms of an element in the gaseous phase each element has unique colour. • The high temperature environment that is generated when a shell explodes causes electrons to jump to higher energy levels in atoms. • When these “excited” electrons fall back to a lower energy level they emit light of particular colours or wavelengths. • Molecular Emissions: can produce similar effects but are results of molecules instead of elements.
CreatingColour In order to achieve these different colours, Pyrotechnicians must add different elements (salts) to the fireworks. • Reds use Strontium and Lithium salts • Yellows & Oranges use Sodium salts • Blues & Purples use copper containing chloride salts, & strontium. These are the most difficult colours to achieve. • Greens use Barium salts
Creating Fireworks Fireworks are more thana pile of chemicals. They must have structure. Fireworks are composed of several different sections: • Shell- a hard paper cylinder. • Fuses: Leader fuse, side fuse , and a series of time delay fuses. • Lift charge - propels firework into the sky. • Stars- the light emitting compounds. • Bursting charge- contains a fuel and a oxidizer.
BOHR'S MODEL OF THE HYDROGEN ATOM: • According to Bohr's theory, the electron can orbit the proton (nucleus) only in certain "ENERGYLEVELS" or principal quantum levels, numbered n=1, n=2, n=3, etc., with n=1 being the normal or GROUND STATE level for the electron. • When the electron is excited up to the n=2 or higher level, a photon of light is absorbed, giving an absorption spectrum. Since the energy levels have a definite spacing, this results in photons of a specific colour or wavelength being absorbed. • When the electron "falls" from a higher to a lower level, light is emitted, giving an emission spectrum.
The BALMER SERIES is the visible spectrum series of emission lines for the Hydrogen atom. These lines are the result of transitions from: [n = 3 to shell 2] red,[n = 4 to n = 2] blue green, [n = 5 to n = 2]blue, [n = 6 to n = 2] violet, all ending in n = 2 energy level. These transitions can be modelled as follows.
Visible Spectrum • Brilliant colours that are seen during a show are from: • Incandesce: Light is created when solid materials are heated to high temperatures, thus creating light • Atomic: When light is emitted by atoms of an element in the gaseous phase each element has unique colour. • The high temperature environment that is generated when a shell explodes causes electrons to jump to higher energy levels in atoms. • When these “excited” electrons fall back to a lower energy level they emit light of particular colours or wavelengths. • Molecular: Molecules can produce similar effects but are results from molecules of compounds instead of elements.
Presented By: Gatorchem and Griffinchem “Colors bursting in air” by Tim Graham edited by T. Knock ChemMattersOctober 1998 Edited and modified February 2000