Atomic Spectra and the Flame Test
Background: Electrons are located on certain energy levels, quantum
numbers: 1, 2, 3, 4, 5, 6, and 7. For example, hydrogen is on 1s1.
Electrons can be raised from one energy level to an excited state if energy is
provided in the system. Heat from a flame can provide enough energy to do this.
The same amount of energy is emitted as light when the electron drops from the
excited state back down to the ground state. Each element will emit light of
different frequencies depending on their electron configuration.
Purpose:
Students will be able to:
a)
Calculate atomic orbitals and electron configuration
b)
Observe atomic emission spectra- energy levels
c)
Identify different wavelengths in the electromagnetic spectrum
d)
Observe Physical and chemical properties of elements
Materials:
Glass
Petri Dish
Goggles
Matches
Methanol
(VERY FLAMMABLE!)
Unknown
Salts
Metal
tongs
Procedures:
1.
Put goggles on and collect necessary materials.
2.
Obtain 0.25 g of sample A and place in petri dish (leave room for the other
samples).
3.
Add a SMALL amount of methanol to sample. (Just enough to moisten the salt)
4.
Light a match and hold in with the metal tongs.
5.
Light the mixture in the petri dish. Note the color after the methanol burns
off.
6.
Repeat steps 2 – 6 with remaining samples.
7.
Put all materials away neatly.
8.
Determine which elements are in the unknowns by using the table below and
record the information in the data section.
|
Cation |
Color
of flame |
|
Ba2+ |
pale
green to yellow green |
|
Ca2+ |
brick
red to yellow |
|
Cu2+ |
green |
|
K+ |
pink
lilac to violet |
|
Na+ |
orange
yellow to yellow |
|
Pb2+ |
blue |
|
Sr2+ |
red |
Data:
Sample Letter
|
Color emitted |
Probable Element |
Element Electron Configuration |
A
|
|
|
|
|
B |
|
|
|
|
C |
|
|
|
|
D |
|
|
|
|
E |
|
|
|
|
F |
|
|
|
Questions and Conclusion:
Directions:
Answer these questions below and then write a one-paragraph summary of what
occurred in the lab.
1.
What subatomic particle is responsible for the production of colored light?
2.
Why do different salts emit different colors of light?
3.
Why do you think the salts have to be heated in a flame before the color is
emitted?
4.
What is the characteristic flame color for Sodium? Lithium? Copper? Strontium?
5.
Strontium and Lithium have similar colors how could the colors be further
analyzed?
Applications
to Everyday life:
a.
Lighting-Sodium lamps appear yellowish. Tungsten in incandescent bulbs emits
white light. Neon emits orange-red light. Xenon in the new car headlights emits
a bluish light.
b.
Fireworks-The color of fireworks is determined by the element or molecule it
contains. For example, red colored explosions are due to Strontium or Lithium
salts.
c.
Astronomy-Astronomers use light and other electromagnetic waves to view the
universe. For example, astronomers use atomic spectra to identify the chemical
elements in stars and planets.