This activity is designed for students to build a scientific argument about the relationship between energy and spectral lines by exploring how light interacts with atoms. In the process, students will examine proposed models of the hydrogen atom and use collected data to analyze the proposed models. They will then select one of the models and write a scientific argument to support their choice. Students will then review additional data to support and/or refute their selection. Based on their analysis, students will revise their selected model and construct a new argument to support their revisions.
This activity will help prepare your students to meet the performance expectations in the following standards:
- HS-PS4-4: Evaluate the validity and reliability of claims in published materials of the effects that different frequencies of electromagnetic radiation have when absorbed by matter.
- HS-PS4-5: Communicate technical information about how some technological devices use the principles of wave behavior and wave interactions with matter to transmit and capture information and energy.
- HS-ESS1-2: Construct an explanation of the Big Bang theory based on astronomical evidence of light spectra, motion of distant galaxies, and composition of matter in the universe.
Science & Engineering Practices
- Developing and using models
- Analyzing and interpreting data
- Constructing explanations (for science) and designing solutions (for engineering)
- Engaging in argument from evidence
- Obtaining, evaluating, and communicating information
- Cause and effect: Mechanism and explanation.
- Energy and matter: Flows, cycles, and conservation.
AP Chemistry Curriculum Framework
- Big Idea 1: The chemical elements are fundamental building materials of
matter, and all matter can be understood in terms of arrangements of atoms.
These atoms retain their identity in chemical reactions.
- 1.5 The student is able to explain the distribution of electrons
in an atom or ion based upon data.
- 1.6 The student is able to analyze data relating to electron
energies for patterns and relationships.
- 1.12 The
student is able to explain why a given set of data suggests, or does not
suggest, the need to refine the atomic model from a classical shell model with
the quantum mechanical model.
- 1.13 Given
information about a particular model of the atom, the student is able to determine
if the model is consistent with specified evidence.
- 1.15 The student can justify the selection of a particular type of
spectroscopy to measure properties associated with vibrational or electronic
motions of molecules.
RST .11-12.7: Integrate and evaluate multiple sources of information presented in diverse formats and media (e.g., quantitative data, video, multimedia) in order to address a question or solve a problem.
RST .11-12.8: Evaluate the hypotheses, data, analysis, and conclusions in a science or technical text, verifying the data when possible and corroborating or challenging conclusions with other sources of information.
- 1.5 The student is able to explain the distribution of electrons in an atom or ion based upon data.
- 1.6 The student is able to analyze data relating to electron energies for patterns and relationships.
- 1.12 The student is able to explain why a given set of data suggests, or does not suggest, the need to refine the atomic model from a classical shell model with the quantum mechanical model.
- 1.13 Given information about a particular model of the atom, the student is able to determine if the model is consistent with specified evidence.
- 1.15 The student can justify the selection of a particular type of spectroscopy to measure properties associated with vibrational or electronic motions of molecules.
By the end of this lesson, students should be able to
- Analyze data from the emission spectra of a hydrogen atom to refine their model of electrons within the atom.
- Analyze student models of electrons within the atom to create and revise a scientific argument of the location of electrons within the atom.
This lesson supports students’ understanding of
- Atomic Emission Spectrum
- Atomic Structure
- Model Based Reasoning
Teacher Preparation: 20-30 minutes
Lesson: 100 minutes
- Hydrogen discharge tube
- Power source
- Diffraction gratings or spectroscopes
- Colored pencils
- Always wear safety goggles when handling chemicals in the lab.
- Students should wash their hands thoroughly before leaving the lab.
- Follow the teacher’s instructions for cleanup and disposal of materials.
- Background Information for Teachers: Since Democritus described the first idea of “atoms” in Ancient Greece, scientists have been investigating the underlying structure of the atom. This task is particularly challenging due to the incredibly small size of atoms and subatomic particles. Since direct observations cannot be made, scientists must make inferences about the properties and structure of the atom based upon observations of energy. Thomson, for example, used his observations of his famous cathode ray experiments to make the connection that the negative charge of the cathode ray was caused by the negatively charged electrons within the atom. The next step of the puzzle was found through Rutherford’s alpha radiation experiments. His results indicated the electrons were found on the outside of the atom, contradicting the previous “plum-pudding model.” At this point, Niels Bohr used his observations of atomic light emissions to further revise atomic models.
In his experiments, Bohr knew that light acts both as a wave and a particle. When observations are made of continuous light spectra, like natural sunlight or incandescent light bulbs, scientists can see every wavelength of visible light. Discontinuous spectra contain only spectral lines of specific wavelengths. Such spectra are produced by elements when sufficient energy is added. Each element releases a characteristic spectrum; these spectral lines observed from an elements emitting light is called an emission spectrum. Since these spectra are unique to each element, scientists can use the observed spectral lines to identify an unknown sample, even to identify the elemental composition of distant stars. Bohr applied his knowledge of spectral lines to establish his model of the atom. When Bohr analyzed the hydrogen atom, which contains only a single electron, he observed only four spectral lines of visible light. Since each color is determined by a specific wavelength of light, he calculated the exact energies being emitted by the hydrogen atom. Bohr then inferred that the electrons surrounding the nucleus within an atom can only be in specific energy levels. Since only four specific colors are visible with hydrogen, instead of random colors or the entire visible light spectrum, Bohr argued there must be some underlying structure which determines the colors emitted. In his model, the electrons were held at these energy levels due to the electrostatic attraction between the positively charged nucleus and the negatively charged electrons. If sufficient energy is added to the atom, the electrons can absorb the additional energy. This extra energy allows the electron to overcome the attractive electrostatic force of the nucleus and move further away to a higher energy level. At these higher energy levels, electrons are said to be “excited.” This arrangement is only temporary, however, and the electron eventually falls back to a lower energy level. Which level it falls to determines which type of electromagnetic radiation is released. When electrons release radiation of high levels of energy, it is considered ultraviolet radiation which is not visible by the human eye. Likewise small emissions of energy release infrared radiation which has too little energy to be seen by the human eye. Only when electrons fall between particular energy levels can visible light be released.
Bohr’s model was the first to place electrons in specific places outside the nucleus. Additional research has further revised his model. Instead of electrons moving around specific “orbits” around the nucleus, subsequent research implies the electrons are found within particular regions around the nucleus in which electrons have a high probability of being found.
- Student Prerequisite Information:
- Parts of the atom (proton, electrons, neutrons) and their properties.
- Properties of a wave: wavelength, amplitude, crest, trough (students should already have an understanding of the inverse relationship between wavelength and frequency).
- Conservation of energy.
- Experimental design and control of variables.
- A basic understanding of direct and inverse relationships (although the terminology is not necessary).
- Light behaves like a particle and a wave.
- Historical models of the atom: billiard model, plum pudding model, and planetary model.
- Experience using and revising scientific models.
For the Student
Part I: Warm Up
- Consider the following questions individually:
a. What do you know about the structure of the atom?
b. Draw what you think an atom looks like. Label the different parts of the atom.
c. What do you think happens to matter (atoms) when you add energy?
Part 2: Exploration
Step 1: Look at the lights in the room or an incandescent light bulb through the spectrophotometer or diffraction grating.
- What do you notice about the incandescent light bulb as seen with the “naked eye,” and observations using the spectroscope or diffraction grating?
a. Observations – eyes only:
b.Observations – spectrophotometer/diffraction grating:
- Using colored pencils, draw what you see from the incandescent light bulb through the spectroscope or diffraction grating.
Step 2: Your instructor will show a gas tube filled with hydrogen gas (hydrogen spectral tube) in a power source. The power source runs an electrical current through the tube at a high voltage. Make observations of the hydrogen gas with your eyes only and then through the spectrophotometer or diffraction grating.
- What do you notice about the tube of hydrogen gas as seen with the “naked eye,” and observations using the spectrophotometer or diffraction grating?
a. Observations – eyes only:
b. Observations – spectrophotometer/diffraction grating:
- Using colored pencils, draw what you see from the hydrogen gas through the spectrophotometer or diffraction grating:
- Compare and contrast your observations of the incandescent light with your observations of the hydrogen spectral tube.
- Which subatomic particle do you think is affected when energy is added to the atom? Explain.
- What do you think happens to this subatomic particle when it absorbs energy?
- What do you think happens to this subatomic particle when it releases energy? Where does this energy go?
- Two students are discussing the following questions: What does the observation of specific colored lines (spectral lines) tell us about how the electrons are organized outside the nucleus? Examine the responses of the two students below.
Download the Student Activity to view the rest of this lesson.