Mr. Sexton's Science Outpost

Nature is worth knowing.

Tag: CHS

Chemistry Students Explore Atomic Emission Spectra

    According to the Bohr model of the atom, electrons are confined to orbits with fixed distances around the nucleus that correspond to specific levels of energy.  Higher energy levels are located farther from the nucleus. When atoms are bombarded with energy, each electron can only absorb the precise quantum of energy needed to move from its ground state to a higher energy level (excited state).  When electrons fall back to the ground state, this quantum of energy is released as a photon of light.  Each element has a unique set of electrons, and therefore, will emit a unique spectrum of photons.  These emission spectra can be used like a fingerprint to identify an element!  Here’s an animated video that I made of the phenomenon.

For Teachers

What makes this argument-driven inquiry lab unique and challenging for most students is the authentic nature of  the inquiry.  Students were given a question and shown the proper use of laboratory tools, but they were not given a procedure, nor a data table.  By considering what data they would need for their argument, and how they would produce and record their data, they gained a deeper understanding of the subject matter, as well as their skill in the science and engineering practices.

After their plans were approved, students began to energize atoms in a bunsen burner flame and analyze the light with a spectroscope.  The spectroscope separates the photons by diffraction and allows each wavelength to be measured for comparison.  In the photo above you can see by the scale that the bright yellow spectral line has a wavelength of 604 nanometers.  Students collected spectral emissions from a variety of known substances, The Bohr Modeland then unknown substances.  Most were able to use a cell phone to capture images through the spectroscopes.  They collaborated by sharing the data via uploads to Google Drive.  In their notebooks their lab reports will include a scannable QR code that will open the link to their shared photos.  Here is a QR code example that will direct you to the section of my website where resources for this lab are located. There are many websites for generating QR codes. This one was done at QR Stuff

After gathering their evidence, each lab group worked together on a whiteboard to create and share an argument that consists of the following:

  • Their claim – They will answer the question, What are the identities of the unknown substances?
  • Their evidence – They will present their photographs of the emission spectra and measurements of prominent lines.
  • Their Reasoning – They will justify their claim by explaining the significance of their evidence by relating it to the principles and theory they have studied.

After sharing and revising their arguments with other lab groups, each student typed an individual report. Their reports were then edited after a double-blind group peer review.  They submitted their edited final draft through Turnitin.


For Students

Here are a few questions for further consideration. Please feel free to comment (extra credit?).

  • In this lab we studied emission spectra.  So what are the differences and similarities between an emission spectrum and an absorption spectrum?
  • We use emission and absorption spectra to study nature at the atomic scale (which is unimaginably small), so how do astronomers use the same phenomena to study the vast universe?
  • What is the relationship between the wavelengths of the spectral lines and their frequency? Can you calculate the frequency for one of the lines in the helium emission spectrum above?
  • What is the relationship between the frequency of the photons and their energy?  Can you calculate the energy for one of the lines in the helium emission spectrum above?
  • What’s up with Planck’s Constant? What does it reveal about the quantum nature of the atom, and the wave-particle duality of light?



Cartoon drawing of Mr. Sexton feverishly writing notes with a test-tube of purple liquid in one hand, and a chalkboard full of equations in the background.







Updated: February 2, 2015 — 3:15 pm


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Interactive Chemistry Notebook

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Table of Contents for the current unit of study (scroll down for prior units):

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Course Calendar


Completed Units – Tables of Contents

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Updated: February 27, 2017 — 12:21 pm

About Mr. Sexton

Photograph of Mr. Sexton

 Joshua Sexton

Curiosity and the delight of Nature led me to study science. The convictions that Nature is worth knowing, and that science benefits humanity, are what drive me to teach.


I began teaching science at Coalinga High School in 2000 and have taught the following course titles: Lab Biology 1, Chemistry, Physics, AP Biology, Earth Science, Integrated Science, and Physical Science. Currently, I teach Biology and Chemistry. I also serve as the Science Department Chairperson, work on the CHS Leadership Team.   I have served at the county level as a presenter for the statewide rollouts of the Next Generation Science Standards.  I have also developed and presented workshops for the annual California Science Education Conference.


  • Teacher of the Year
    Coalinga High School – June 2014
    Named Coalinga High School’s Teacher of the Year for 2013-14
  • 2013 Region VII Educator of the Year Finalist
    California League of High Schools – November 2013
    Selected as one of seven Educator of the Year finalists for Region VII of the California League of High Schools which encompasses Fresno, Kern, Kings, Madera, Mariposa, Merced, and Tulare counties. Congratulations to Region VII winner, Paul Lake who went on to be named the overall CLHS California Educator of the Year!


I began my higher education at Cuesta Community College where I completed general education requirements and worked as a tutor, grader, and lab technician. I was especially inspired by my instructors Joe Brundage (chemistry), and Nancy Mann (biology). After transfer to Humboldt State University, I was invited by Dr. Jacob Varkey to do genetic research with a Howard Hughes fellowship and an HSU grant. In Dr. Varkey’s lab we worked to map and characterize the genes responsible for male-specific meiosis in the nematode C. elegans. I received my Bachelor of Science degree in biological sciences with an emphasis in molecular biology from Humboldt State University. Also at HSU, I completed the year long credentialing program for teachers while student-teaching at McKinleyville High School. During this time, I received significant support and guidance from teacher/mentors Sheila Rocker-Heppe and Dr. Casey Lu. I received my California Single Subject Credential in Life Science in 1999 and later added a chemistry credential by CCET examination.


I am a deeply in love with my wife Rebecca and our three children, Clover, Leela, and Sage. I enjoy guitar, cooking, gardening, surfing, hiking/backpacking, camping, word games, my pets, fantasy football, teaching and learning.

“The scientist does not study nature because it is useful; he studies it because he delights in it, and he delights in it because it is beautiful. If nature were not beautiful, it would not be worth knowing, and if nature were not worth knowing, life would not be worth living.” ― Henri Poincaré

Cartoon drawing of Mr. Sexton feverishly writing notes with a test-tube of purple liquid in one hand, and a chalkboard full of equations in the background.

Updated: September 23, 2016 — 3:01 pm
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