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Kimberly A' LawlerSagarin, Chemistry 100, Fall 2005

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Incandescence is the emission of light from a warm or hot object. ... But did you know that chemistry is behind these amazing displays? ... – PowerPoint PPT presentation

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Title: Kimberly A' LawlerSagarin, Chemistry 100, Fall 2005


1
Kimberly A. Lawler-Sagarin, Chemistry 100, Fall
2005
Color and the Chemistry of Fireworks
Luminescence
Introduction
Luminescence is defined as the emission of light
without heat. That is, any emission of light is
not solely due to high temperatures. There are
many forms of luminescence, some of which we will
discuss later in the semester. The bright colors
in firework displays are caused by the
excitations of atoms or small molecules. Atoms
consist of two main parts The nucleus - the
core of the atom. The nucleus consists of two
types of smaller particles, protons and neutrons.
Protons have a positive electrical charge,
whereas neutrons are neutral, so the nucleus
of the atom is positively charge Electrons -
small negatively charged particles exist outside
the nucleus. In our modern model of the atom,
all the electrons in the atom do not have the
same energy. Electrons occupy different energy
levels. It is these energy levels that are behind
the color of fireworks. Essentially, an electron
in a lower energy level can be promoted to a
higher energy level by adding energy (such as
during the explosion of a firework). Now, the
atom has excess energy. However, this "excited"
atom has a very limited lifetime. It quickly
returns back to the lower energy state. One way
it can do this is by emitting a photon.
Everybody enjoys fireworks on the fourth of
July! Explosions, bright light and brilliant
colors lead to beautiful displays that make
millions oooh and ah. But did you know that
chemistry is behind these amazing displays? To
understand the role of chemistry, lets take a
look at two phenomena that are responsible for
the colors of fireworks incandescence and
luminescence.
Incandescence
Incandescence is the emission of light from a
warm or hot object. We encounter many examples of
incandescence in our daily lives. A common
example is the (incandescent) light bulb. A
tungsten filament is sealed into an evacuated
glass bulb. When heated, the filament releases
light. Other examples of incandescence are the
"red hot" coals in a barbeque grill, the "red
hot" or "white hot" pieces of glowing metal on
might see the hands of a blacksmith in an old
western movie, or even just the heated carbon
particles in a candle flame. Below is a picture
of one of our chemistry majors, Mike Zickus,
burning magnesium metal. Magnesium metal (Mg)
combines with oxygen (O2) to form magnesium oxide
(MgO). The brilliant white light is produced from
the high temperatures generated by the heat
released in the reaction. Magnesium powder is
used in many types of fireworks because of this
property. This explains the intense light given
off by fireworks, but to describe the colors, we
must look to luminescence.
Figures 2-3 Fireworks from the 2004 Batavia,
Illinois fireworks show.
Figures 4
The wavelength of light emitted has an energy
that corresponds to the energy difference between
the two levels. This determines the color we see.
Atoms of different elements have different
spacing between their energy levels, leading to
different colors. Thus, a variety of different
substances are used to produce the colors we see
in a fireworks show.
Figures 5 Here, methanol burns in the presence
of various metal salts, each salt giving rise to
a different color. Clockwise, from top orange
(sodium), yellow-green (barium), green-blue
(copper), red (strontium), violet (potassium).
Figures 6 Red fireworks are commonly created by
lithium or strontium salts.
Figure 1 Incandescence produced during the
combustion of magnesium metal
Charitable Toy Drive Help us celebrate national
chemistry week by contributing to our toy drive
for local charities. Sponsored by the Student
Affiliates of the American Chemical Society and
the students in Chemistry 100 and the Common
Experience Program. Collection will take place
from Oct. 16th - 31st! Drop off boxes can be
found near the main entrances of the Frick Center
and the Library, or toys can be left at 221 SC.
To arrange an on campus pick up or if you have
questions call x3204.
So, the next time you are enjoying a fireworks
show, think of chemistry!.
  • References
  • Nassau, K. The Physics and Chemistry of Color
    The Fifteen Causes of Color 2nd ed. Wiley New
    York 2001.
  • Helmenstin, A. M. "The Chemistry of Firework
    Colors" http//chemistry.about.com/library/weekly/
    aa062701a.htm (accessed February 2005).
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