The Emission Specturm of Hydrogen Gas

The Emission Specturm of Hydrogen gas Lesson Materials and Resources: • • • Powerpoint presentation reviewing models of the atom and introducing light and the electromagnetic spectrum. Several different gas discharge tubes and power supplies. Hand held spectroscopes: image from: http://chem.wisc.edu/deptfiles/genchem/lab/labdocs/modules/spectro/spectrodesc.htm • • • • • A classroom with a window and an overhead light. Vernier probe software: Vernier Spectrometers, computers with Logger Pro 3 software installed, fiber Optic accessory, hydrogen gas discharge tube, dischare tube power supply. Ryberg Constant lab: http://www2.vernier.com/sample_labs/VSPEC-08-COMP-rydberg_constant.pdf Light CalculationsWorksheet (example available below) for practice with mathematics involved. Applet: http://phet.colorado.edu/en/simulation/hydrogen-atom Technology Tools and Materials: • Vernier probe software: Vernier Spectrometers, computers with Logger Pro 3 software installed, fiber Optic accessory, hydrogen gas discharge tube, dischare tube power supply. Background Information (prior knowledge): Students should come into this unit with a strong understanding of the subatomic particles that make up an atom (protons, neutrons, and especially electrons, relative sizes and charge, etc.). Although the lesson begins with a quick review of the early models of the atoms, student should have learned the basics of the Bohr model before beginning this lesson (i.e. nucleus = protons + nuetrons, electrons ‘orbiting’ around, etc.). Students should have strong algebraic skills (completed Algebra 1 at the least). Students should have a basic understanding of element symbols, atomic number, atomic mass. Useful Vocabulary: New Vocabulary Word Electromagnetic Spectrum Visible light Wavelength Meaning All wavelengths of the radiation emitted from the sun. EM radiation with wavelengths between 400nm – 700nm. ROY G BIV The distance from crest to crest of a wave. The wavelength indicates the type of EM radiation (ex. microwave, infrared, UV, visible). Knowing the wavelenth of visible light tells you the color the light. Amplitude Speed of light ( c ) Frequency The height of the wave. Related to the intensity (strength) of the light. 2.99x108 m/s All EM radiation travels at this speed. How many waves pass through a given point per second. Measured in Hertz (1Hz= 1s-1). A ‘particle’ of light. A photon has no mass, but carries a quantum of energy. An ‘energy packet.’ Photon Quantum Essential Questions to be answered (Grand Challenges): How is the emission spectrum of Hydrogen gas explained by Bohr’s model of the atom? Misconceptions: There are very few misconceptions, because students rarely come into chemistry with any knowledge of what an atom is at all – aside from just something small that looks kind of like the solar system. They do not usually know anything about the connection between light and electrons, and they know very little about how that model was derived. • Electrons are so small we cannot observe them in any way in a classroom setting. Lesson Procedures: CLASS 1: 1. Set up different gas tubes around the room and turn out the lights so students walk in to what looks like a little light show. Introduce lesson by asking the essential question (i.e. ‘how do these tubes, particulary the hydrogen gas tube, relate to our understanding of the atomic model?’). 2. Ask the students to help you make a list of what they might need to know to understand this. Put this list on the whiteboard. Hopefully it will look something like this: What is light? What is in these tubes? Why are different tubes emitting different colors of light? What are the models of the atoms that we know? 3. Review the atomic models they have learned so far: Dalton’s Billiard Ball, JJ Thomson’s Plum Pudding, Rutherford’s Gold Foil, Bohr’s Planetary Model (see Powerpoint for images). 4. Hand out handheld spectroscopes. Have students look at white light and then a few different discharge tubes. What do they notice? 5. Lecture/discuss light and the electromagnetic spectrum with students (again see Powerpoint). If there is time have students break into groups of 3-4 and each investigate a type of electromagnetic radiation for 15 minutes – then present what they found informally to the class. 6. Discuss/do example problems relating the energy (E) of a photon, the wavelength (λ) if the light, the color of the light, and the frequency (ν) of the radiation. 7. HW: Practice problems relating the energy (E) of a photon, the wavelength (λ) if the light, the color of the light, and the frequency (ν) of the radiation. An example HW worksheet is at the end of this lesson. CLASS 2: 8. Give students time to compare their work with a partner. Take questions / go over problems. 9. Review essential question. Review what we have learned so far: light, models of the atom (i.e address which of the things on the whiteboard list we have covered). 10. Perform Vernier Lab: The Ryberg Constant – this lab includes a prelab exercise the students should have to submit in teams before moving on to doing the lab itself. 11. At the end of the lab discuss with Powerpoint slides how what they did relates to the Bohr model. 12. As students finish the lab have them play around with the following applet to reinforce the knowledge they just gained from lab: http://phet.colorado.edu/en/simulation/hydrogen-atom 13. Have students each write a quick paragraph to hand in (or email) summarizing the lesson using at least 4 new vocabulary words. Assessment Procedures: Formal Assessments: • The HW due at the beginning of class 2 should be graded. • The pre-lab exercise at the beginning of the lab should be graded. • The paragraphs written at the end of class 2 should be collected and graded. • The lab data-analysis should be collected the day after the lab is performed and graded. • All of the material in this lesson should appear on the unit exam at the end of the entire Atomic Models, Light, and Electrons Unit. (*this exam is not included as every teacher might have a different entire unit). Informal Assessments: • Every ‘lecture’ should be more of a discussion where the appropriate vocabulary is used by both teacher and students. • • Students presenting their information on the electromagnetic spectrum. At the beginning of class 2 the teacher should gain a strong idea of how well students are grasping the problems. If they are having trouble on calculations do more practice problems and lengthen the amount of time spent on class1 material before moving on to the Vernier Lab. Accommodations/Modifications: • Students who are not as strong in math can look at the several different gas discharge tubes and use colored pencils to draw the emission spectrum of each gas. Have students make hypothesis as to why each spectrum is different. Walk students through the hydrogen emission spectrum and Bohr’s model of an atom rather than have them do the calculations. Reproducible Materials: • Light Calculations Worksheet (example included at end of this lesson) Explorations and Extensions: There are several ways to extend this lesson. Lesson Development Resources: The following resources were drawn upon to design this lesson. 1. 2. The Ryberg Constant Lab, 2010 Vernier Software & Technology My fellow RET teachers at the NSF RET at BU 2012 Reflections: (to be filled in upon teaching this lesson) Useful Information: E=hv R = 2.18 x 10-18J c=λv h = 6.63 x 10-34Js c = 3.00 x 108 m/s PUT ANSWERS TO MATH PROBLEMS ON LINE AT RIGHT; SHOW YOUR WORK; UNITS COUNT 1. What  is  the  frequency  of  light  with  a  wavelength  of  700nm? 1. ___________________ 2. What  color  is  the  light  in  question  1? 2. ___________________ 3. How  much  energy  is  released  when  an  electron  fall’s  from  n=5  to  n=2? 3. __________________ 4. What  is  the  frequency  of  the  light  in  question  3? 4. __________________ 5. What  is  the  wavelength  of  the  light  in  question  3? 5. __________________ 6. What  color  is  the  light  in  question  3? 6. ___________________