Lab: Electrons and Emission Line Spectra
Name: _______________
Background
Bohr proposed that an electron is found only in specific circular paths, or orbits, around the
nucleus. As a result, each orbit has a fixed energy called an energy level. These energy levels are
like the rungs of a ladder. The electrons cannot be found in between these energy levels, just like
a person cannot stand in between the rungs. (See Figure A) Electrons must gain energy (become
excited) to move up energy levels. Electrons can become excited by heat, light, electricity etc.
Once at the higher energy level the electrons are said to be in an excited state. These excited
electrons are unstable and eventually fall back down to their lower energy levels (ground states)
releasing the energy that they had gained when they were initially excited. This energy is released
in the form of light and is what Bohr observed.
Figure A
White light will produce a continuous spectrum when viewed using a prism or
spectroscope. Different colors of light have different energies. (See Figure B)
When electrons of an atom are excited they will release different colors of
light as they fall back to ground state (this is called emission line spectra. The
colors of light correspond to the amount of energy released (See Figure C).
Using a spectroscope you can view the emission line spectra. Different
elements produce different spectra that are unique enough to be considered
a “fingerprint” of the element.
C
Figure B
Which arrow demonstrates when energy is being absorbed? ___________
Y
Which arrow demonstrates when energy is being emitted? ____________
Z
Which arrow demonstrates when light would be given off by the atom?
_________________
Why do electrons move to higher energy levels? _____________________
_____________________________________________________________
Emission Spectra
Element
Color:
http://chemistry.bd.psu.edu/jircitano/periodic4.html
R
O
Y
G
B
I
V
Sodium
Calcium
Copper
Barium
Potassium
Strontium
Energy: Low
High
Demonstration Objective:
In this demonstration you will:
1. Observe the emission spectra for various compounds.
2. Use a flame test to observe the color produced when metal ions are heated.
Part A. Teacher Demonstration with student helpers:
The chart below will be completed as a class.
Metallic Ion
Group prediction for what the Color
of Flame will be
1.
Sodium chloride
2.
Calcium chloride
3.
Copper Chloride
4.
Barium Chloride
5.
Potassium chloride
6.
Strontium Nitrate
Actual Color of Flame
Part B. Atomic Model Drawing
* When drawing atomic models, you start filling electrons into the 1st energy level and cannot add electrons in the
next level until the previous energy level has been completely filled.
What is the maximum # of electrons found in each energy level?
1st _____
Element
2nd _____
3rd _____
Ground State Atomic Drawing
4th _____
Element
Sodium
Atomic# _____
Barium
Atomic# _____
Calcium
Atomic# _____
Potassium
Atomic# _____
Chlorine
Atomic# _____
Strontium
Atomic# _____
Copper
Atomic# _____
Nitrogen
Atomic# _____
Lithium
Atomic# _____
Oxygen
Atomic# _____
Ground State Atomic Drawing
Questions:
1. How is an emission spectra of an atom produced?
2. Explain how colors in the flame test are produced.
3. What does it mean when the electrons are “excited”?
4. How are the electrons “excited” in this experiment?
5. Draw a Bohr diagram for Sodium (Atomic # 11) and Chlorine (Atomic # 17) in the ground state.
Na
Cl
6. Draw a Bohr diagram for Sodium (Atomic # 11) and Chlorine (Atomic # 17) when an electron has
been excited to the 5th energy level from the third energy level.
Na
Cl