Lab – Spectral Analysis of Excited Elements
Name: ______Period: ______Today’s Date: ______Due Date: ______
Prelab Discussion: Annotate as you go (Underline Vocabulary words we’ve had in class)
The electrons of an atom, as described by Neils Bohr, travel around the nucleus in discrete Energy Levels (AKA: Shells). These resemble satellites orbiting the earth at various distances and are often illustrated using an atom’s Electron Configuration.
When the electrons are in their lowest energy level(s) permitted, they are said to be in GROUND STATE. There are however situations whereby the electrons absorb energy and leave their original location. They move to a higher energy level(s). At this point they are in the EXCITED STATE.
This situation is very short lived. When the electrons fall back down to their original location (GROUND STATE) the energy that they had absorbed is now given off as Electromagnetic radiation. Of which, some of this energy may be a blend of various colors of visible light. (see FIGURE 1)
FIGURE 1
In this Bohr diagram on an atom, a Photon represents a measureable “packet” of energy. Initially it is absorbed by electrons, causing them to achieve the “EXCITED STATE”. This is them followed by a Photon of energy (sometimes visible light) being released to achieve “GROUND STATE” once again.
This light can better be understood by separating out the individual colors that are blended to form the color your eye detects. This is accomplished by using a Prism to separate the colors of light similar to how the colors of a rainbow are separated from sunlight when it passes through a window. (see FIGURE 2)
FIGURE 2
This picture shows a “Light Bulb” (Discharge Tube) filled with Hydrogen gas. As the “EXCITED” electrons fall back to “GROUND STATE”, light exits the bulb. This light is a mixture of many individual colors. The prism separates these colors to form a “SPECTRUM” that is unique for Hydrogen and every element in existence.
Each element will have its own unique blend of colors. Using the technique mentioned above, we can record them for comparison. In general, this is the method used to understand the elements that make up our sun and distant stars. (see FIGURE 3)
FIGURE 3
This illustration shows the spectral lines created for Carbon, Helium and Hydrogen. In reality, they would have color too, but printing that would be costly. Take notice of the unique pattern for each element. In a way, this can be considered an element’s SPECTRAL FINGER PRINT.
These lines can be used to identify an element present in an unknown sample.
PreLab Questions: Before you can begin your work, you must understand the basic concepts:
1. What is the benefit of the Bohr Diagram?
2. What is responsible for making an electron jump up an energy level?
3. What happens immediately after that?
4. How are Spectral Lines formed?
5. Predict the purpose of this lab.
Objective: In this lab I will
Ø Compare the electron configuration of atoms in their GROUND STATE vs. EXCITED STATE
Ø Identify the source of the light emitted from the elements trapped within a Discharge Tube
Ø Witness and draw spectral lines of elements after their electrons are excited.
Ø Compare spectral lines of various elements
Ø Predict the identity of an element based on its spectral lines
Materials: High-voltage power supply
Discharge Tubes with various elements in them
Spectroscope
Crayons
Safety Do NOT touch the high-voltage power supply.
Do NOT touch the Discharge Tubes (light bulbs).
No Horseplay
Procedures: Emission Spectra of Gaseous Elements
1. The teacher will load various spectrum tubes into the high-voltage power supplies.
2. Aim your spectroscope at the glowing tube. While looking through the devise you will notice the sides have many colorful columns of light. You may have to rotate the eyepiece to visualize it more clearly.
3. In the data section below (and later in your lab report), sketch the appearance of the emission spectrum and record the colors of the predominant spectrum lines. (Use crayons)
Data: Use your observations to sketch the spectral lines you witness in your spectra analysis of the various Discharge Tubes
Hydrogen
Oxygen
Water Vapor
Nitrogen
Neon
QUESTIONS:
1. For each of the samples used in this lab (except for Water Vapor), complete the chart to illustrate the electron configuration of the atoms in GROUND STATE and what they may resemble when they are in the EXCITED STATE.
Element / Electron Configuration – GROUND STATE / Possible Electron Configuration – EXCITED STATEHydrogen
Oxygen
Nitrogen
Neon
2. What is the source of the light emitted from the elements trapped within a Discharge Tube?
3. Why do the line spectra of the various elements differ?
4. How are you able to use the spectrum of unknown substances to establish their identity?
5. Why did each gas only show a color when electricity was passed through it?
6. How does the Bohr model of the hydrogen atom explain the spectrum of hydrogen?
7. What is one practical application of passing an electrical charge through a gas?
8. Using the Data presented in the illustration below, predict which element(s) are present in the star spectrum on the bottom. Explain your answer.
Formal Lab Report Check-off list. Once you have completed all the tasks below, check them off.
o Title Page
o Objective
o Materials List
o Safety
o Procedures – In your own words
o Data
o Questions
o Conclusion
o The formatting looks NICE!