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Kimberly A. LawlerSagarin, Chemistry 100, Fall 2006

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The bright colors in firework displays are caused by the excitations of atoms or ... 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 2006


1
Kimberly A. Lawler-Sagarin, Chemistry 100, Fall
2006
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
chargee Electrons - small negatively charged
particles that 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
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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