Lesson 2: 1.2 Mass Spectra of Elements
Duration of Days: 1
Lesson Objective
Explain the quantitative relationship between the mass spectrum of an element and the masses of the element's isotopes.
How does a mass spectrometer separate particles, and what does this tell us about an element's isotopic abundance?
Why are atomic masses on the periodic table rarely whole numbers?
Isotope
Mass Spectrometry
Relative Abundance
Weighted Average
Monatomic Ion
Learning Objective 1.2.A; Suggested Skill 5.D (Mathematical Routines/Graphical Analysis)
Students learn to analyze graphical data from mass spectrometry to identify an element and calculate its average atomic mass based on fractional natural abundance. Note: This is strictly limited to singly charged monatomic ions.
Mass spectrometry is widely used in forensic science for drug testing, carbon dating archeological artifacts, and analyzing soil samples on Mars rovers.
Support: Use a physical simulation (e.g., rolling steel ball bearings of different weights past a magnet) to conceptually illustrate how a magnetic field deflects masses differently.
Extension: Provide a mass spectrum of an unknown element with missing baseline values and have students mathematically deduce the identity of the element using the weighted average.
AP-style multiple-choice questions presenting a mass spectrum graph where students must estimate or calculate the average atomic mass and identify the element. This is located on AP Classroom.