Download Atomic Spectrum

Flame Tests of Metal Ions -- Chemistry Laboratory
Purpose: To discover the different frequencies of light that is emitted by various metallic ions.
Pre Lab Questions:
Electromagnetic spectrum
1. What are the colors of light in the visible spectrum in order of increasing energy (decreasing
wavelength)?
2. Define atomic emission spectrum.
3. Define ground state
4. Define Photon
5. How can electrons become excited?
6. What generally happens when electrons loose extra energy?
Background information:
Using your text book and the handout include information about the electromagnetic spectrum. Make
sure to include information about the color of light in the visible spectrum, the energy of the light, and
how the light is produced.
Safety:


Follow appropriate safety procedures when operating the burners. Tie back long hair and
secure loose clothing.
Many of the salts used in this experiment are toxic. Be sure to wash hands thoroughly after
coming into contact with any of the substances.
Materials
Metal Salts
 10 metal salts (s)
 Unknown (a mixture of 2 or more of the above
salts)
Equipment
 Bunsen Burner
 Striker
 Cotton Swab
 Beaker of water
Procedure:
1. You will be rotating through 7 different stations in a clockwise direction. You will have no more
than 4 minutes at each station.
2. If the burner is not lit, follow the appropriate procedures for lighting the burner. Pick up a
correctly labeled cotton swab or paperclip loop.
3. Dip the wire loop into the beaker of distilled water. Then dip the wire loop into the beaker of
metal salt crystals so that a FEW crystals adhere to the loop. Don’t pick up too many crystals or
the will make a mess! Remember, some of these are toxic and we do not want crystals lying
around the station to get onto your skin or into your eyes.
4. Place the wire loop into the burner flame. Observe the color produced and record it in a table
you construct. Watch carefully because some colors will not last long. Be as descriptive as
possible. (e.g. red orange instead of orange)
5. Rotate to the next station. DO NOT LEAVE THE FLAME UNATTENDED. If another group is ready
to use your station, you may leave the flame in their care. Otherwise, extinguish the flame by
turning off the gas before leaving your station.
6. Repeat steps 1-5 until you have observed all six metal salts and the unknown.
Observations:
Record you observations as directed in the procedure. You will need to create a table to make your
observations on similar to the one shown below:
Element No.
1
Metal Salt
Strontium Chloride, SrCl2
Detailed Observations
Post Lab Questions:





What is the unknown metal ion? Describe what evidence you have to support your answer.
Explain how colors are produced by the metal ions. Include terms such as ground state, excited
state and photon in your explanation.
Explain how a forensic scientist could use similar methods to determine an unknown substance
at a crime scene.
List the electron configurations for the metal ions used in the compounds you tests. You may
use the noble gas configurations if you would like.
Draw the orbital box diagram for each.
Atomic Spectrum
The Atomic Spectrum is a series of lines of color produced when light from an
excited atom is passed through a prism. It is also known as a line spectrum.
Each element has its own unique atomic spectrum and address. Because of their
unique nature, atomic spectra are also referred to as the "fingerprints of the
elements." The series of lines of color that an atom will produce is related to the
locations of the electrons on that atom and their relationship with the nucleus.
Atomic spectra were fundamental pieces of experimental information used by
chemists in the development of the electronic structures of atoms. By studying the
colors emitted by the different elements, it is possible to work backwards to the
sources of those colors. In this way it is possible to determine the electronic
structures of the elements. Most of the basic information known today about
electronic structures was derived from studying the light emitted by the atoms.
The process of exciting an atom, involves adding energy to the atom. This can be
done in a variety of ways. Simply heating a sample of an element up in an open flame
will excite electrons. Passing electricity through a sample of an element will excite
electrons. The colored lights observed when sky rockets explode are a result of
burning gunpowder exciting electrons within atoms of elements packed with the gun
powder.
Electromagnetic Radiation Spectrum
The Electromagnetic Radiation Spectrum, or EMR Spectrum, is a full "rainbow" of
all colors of light, both visible and non-visible. To a large degree it is a theoretical
spectrum, in that no real system is capable of producing all colors of emr. The EMR
Spectrum is generally broken down into three regions--visible, ultraviolet and
infrared. By tradition, the spectrum is shown with the colors in order of increasing
wavelengths, decreasing frequencies and decreasing energy values.
Energy Level
An energy level is a specific location on an energy level diagram that
corresponds to an allowed specific energy content of an electron. Bohr
Theory said that the electron was restricted to existing only at specific
levels of energy and would never be found with energy content
between those levels. This component of the theory was based on work
done by Max Planck.
Excited State
The Excited State according to Bohr Theory is a position on an energy level diagram
that contains more energy than the Ground State. When an electron is exposed to
energy it may absorb some of that energy. If it does, it will rise up the energy level
diagram to a new position that corresponds to the higher energy content. An electron
in an excited state is not in its most stable position. An electron in an excited state
will eventually return to the Ground State.
Electron Transition
An electron transition is the movement of an electron from one energy
level to another. If an electron moves from a low energy level to a
higher energy level it does so by gaining energy. If it moves from a
higher energy level to a lower energy level, it does so by releasing
energy. The released energy is in the form of electromagnetic
radiation. The energy content and wavelength of the released
electromagnetic radiation will correspond to the difference in energy
content of the two levels. This transition is also known as a Quantum
Jump.