CHEM 132 Lab
Western Carolina University
Name __________________________
Chemistry 132 Lab 03
Lab Section______________
Flame Test and Electron Configuration
Prelaboratory Exercise
Answer the questions below on a separate sheet of paper and turn in the paper at the start of lab.
Reading over the lab handout will help you find the answers.
1. What color of light does a low-pressure sodium street lamp give off?
2. What color of light does a true neon light give off?
3. What element on the periodic table has the electron configuration 1s2 2s2 2p6 3s2 3p5?
Introduction
Flame Tests
Atoms for each element on the periodic table have their own characteristic spectrum, which are
colored lines separated by dark areas. An atomic spectrum is produced when light emitted from
heated (high-energy) atoms is passed through a prism. When electrons in these hot atoms absorb
energy, they can attain higher energy levels. In order to return to the lower, more stable energy
levels, electrons release energy. If the energy released is the same frequency as visible light, the
element produces a characteristic color, which can be used in identifying that element.
An example of such a phenomenon is the difference in the light given off from a neon light and a
low-pressure sodium street lamp. Think back to the street lights lining the roads of a city. These
lamps tend to give off a warm yellowish glow. Now think about the lights declaring a local
restaurant as OPEN, usually showing up as bright red or blue. The red light given off is a true neon
light, since the atoms inside the glass tube are atoms of neon gas. Blue lights, while often called
neon signs, don’t actually have neon gas inside the tubes that light up. (A different element is used
to produce blue light.)
When an electric current is passed through the gas in one of these lights, the atoms in the tube
absorb energy, and the electrons are raised to a higher energy level. When the electrons fall back to
their original level they give off the extra energy, and light of a characteristic color is produced.
Electron Configuration
Electron configuration shows how electrons in an atom are arranged by shells and subshells, starting
with the lowest energy level and counting up. The number of electrons in each subshell is written
as a superscript.
Think of the electron configuration of an element (or exact position on the periodic table an element
holds) as if it were directions from your house to another city. When leaving home, you always
start from your driveway and take the route that gets you to your proper destination.
1
CHEM 132 Lab
Western Carolina University
Writing an electron configuration of an element can be done by following these simple steps:
1. Locate the element on the periodic table.
2. Write the filled sublevels in order going across each period (left to right) starting at the lowest
energy level and smallest subshell.
Energy levels: 1 < 2 < 3 < 4 < 5 < 6 < 7
Subshells: s < p < d < f
3. Count the number of electrons in the sublevel for the element and complete the configuration.
The following is an example of figuring out the electron configuration for chlorine (Cl), using the
periodic table. Remember that the main shell is given by the period (row) number of the periodic
table.
Period
Sublevel
Sublevel Blocks Filled
1
1s sublevel (H → He)
1s2
2
2s sublevel (Li → Be)
2p sublevel (B → Ne)
2s2
2p6
3
3s sublevel (Na → Mg)
3p sublevel (Al→Cl)
3s2
3p5
Final electron configuration for chlorine: Cl : 1s2 2s2 2p6 3s2 3p5
Abbreviated electron configuration for chlorine: Cl: [Ne] 3s2 3p5
The total number of electrons found in an atom of chlorine is 17, while the number of valence
electrons for chlorine is 7. Valence electrons are the electrons in the s and p sublevels with the
highest energy level (or all electrons after the previous noble gas in the main groups).
Figure 1 - Electron Configuration and the Periodic Table
In today’s lab, flame tests will be used to see how the valence electrons of an atom are excited by
the energy of the flame, and then release that energy by giving off a characteristic color of light.
2
CHEM 132 Lab
Western Carolina University
Procedure
Flame Tests
Materials: Bunsen burner, spot plate, flame-test (nichrome) wire, cork, 100mL beaker, 1 M HCl,
0.1 M solutions (dropper bottles) of: CaCl2, KCl, BaCl2, SrCl2, CuCl2, NaCl, and unknown
solutions.
CAUTION! 1 M HCl is corrosive! Use gloves and be careful when you handling it. Wash off
any HCl spills on the skin with tap water immediately after they occur for 10 minutes. Then
wash area with soap and water.
Obtain a spot plate, flame-test wire, and cork stopper from your equipment bin. One end of the
flame-test wire should be bent into a small loop, so the other end can be secured into a cork stopper.
Pour a small amount (about 10-15 mL) of 1 M HCl into the 100 mL beaker. Wash and then rinse
the spot plate in distilled water. Place 6-8 drops of each test solution into separate wells of the spot
plate. Label the spot plate diagram below to match the solutions. Make sure the different solutions
don’t become cross contaminated!
Spot plate diagram
Adjust the flame of the Bunsen burner until it has a blue cone flame. Clean the test wire by dipping
the loop into the HCl beaker and then placing it into the flame of the Bunsen burner. After this,
rinse with de-ionized water and then dry in the flame. If you see a strong color in the flame while
heating the wire, repeat the steps above until only a slight coloration appears when the wire is in the
flame.
Observing Flame Colors for Known Solutions
Allow the cleaned wire to cool and then dip it into one of the solutions on the spot plate. Make sure
that a thin film of the solution adheres to the loop. Put the loop into the top of the blue cone flame
and record the color you observe in Table 1. For each solution, it is the first element (the metallic
element) in the formula that is responsible for the color.
Notes:
Make sure you properly clean the wire loop between each color test! Record the color for each
flame test in the blanks below.
The color of potassium in the KCl flame is short-lived. Be sure to observe the color of the flame
from the KCl solution within the first few seconds of heating. Repeat each flame test until you can
describe the color of the flame produced.
3
CHEM 132 Lab
Table I
Solution
Western Carolina University
Flame Colors for Known Solutions
Element
Color of Flame
CaCl2
Ca
__________________________
KCl
K
__________________________
BaCl2
Ba
__________________________
SrCl2
Sr
__________________________
CuCl2
Cu
__________________________
NaCl
Na
__________________________
Identifying Unknowns by Flame Color
Follow the same procedure above for your three solutions containing unknown metallic elements,
and record the data in Table 2. Be sure to record the ID number for your unknown solutions.
Table 2
Flame Colors for Known Solutions
Unknown ID
Color of Flame
Element
__________
_________________
____________
__________
_________________
____________
__________
_________________
____________
4
Figure 2
Use this periodic table to write the electron configurations for the problems on the next page.
4
CHEM 132 Lab
Western Carolina University
Electron Configuration of Neutral Atoms
Atom
O
Na
Ca
F
C
Li
K
Sr
Br
Cu
S
Electron Configuration
Abbreviated Electron
Configuration
# of Valence
Electrons
Electron Configuration for Ions
Ion
O2Na+
FLi+
Sr2+
Electron Configuration
Abbreviated Electron
Configuration
# of Valence
Electrons
Questions:
1. Why is the electron configuration for the oxygen atom different than the electron configuration
for the oxygen ion?
2. How many valence electrons are found in an atom of chlorine?
3. How many valence electrons are found in a chloride ion (Cl –1)?
5