Mass Spectrometry of Elements
▶︎ Watch it animatedinteractive step-through · ~3 min · optionalA mass spectrometer sorts the atoms of a sample by mass and counts how many land at each mass. Run an element through one and you get its isotopes and their relative abundances: a spectrum of peaks where position is mass and height is how common that isotope is. The periodic table's average atomic mass is built directly from that spectrum.
The one idea to hold onto is that the average atomic mass is a weighted average, not a midpoint. It is pulled toward whichever isotope is most abundant, so it usually sits nowhere near halfway between the lightest and heaviest peak.
The work
3 ways in · any order
Lesson
Mass Spectrometry
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A mass spectrum encodes isotope masses and abundances as peaks. The lesson reads spectra both ways, from peaks to the weighted-average atomic mass and back, and closes with a ten-scenario check on what each peak's position and height actually mean.
Diagnostic
10-item topic check
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Ten items on reading a mass spectrum: matching peaks to isotopes, telling a peak's position (mass) from its height (abundance), and computing the weighted-average atomic mass rather than a simple midpoint.
Targeted Practice
Drill a single misconception
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Pick one of the failure modes you missed and drill it on its own. The round is adaptive: two correct in a row clears the misconception and moves you to the next.