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Chadwick and the Neutron | When Neon's Mass Didn't Add Up

2025-07-21

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Learn what lead up to James Chadwick's discovery of the neutron: Confusion over 2 masses of neon, JJ Thomson and Francis Aston's early mass spectrometry (mass spectrograph), and Chadwick's groundbreaking radioactive experiments to discover the neutron.

0:00 Early Mass Spec (Mass Spectrograph) Experiments

2:10 Puzzle of Neon's 2 Masses

2:47 What We Already Knew About Atomic Structure

3:18 Mysterious Gamma Radiation

4:26 Chadwick's Experimental Set-Up

6:35 Discovery of the Neutron

7:20 Neon's 2 Masses Explained

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Citations:

https://theanalyticalscientist.com/issues/2013/articles/sep/the-origins-of-mass-spectrometry

https://openstax.org/books/chemistry-2e/pages/2-2-evolution-of-atomic-theory

Images:

By Not Mentioned - First World War.com, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2969861

By Unknown author - http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1922/aston.html, Public Domain, https://commons.wikimedia.org/w/index.php?curid=18253663

By Francis William Aston - "Positive Ray Parabolas". Isotopes. London, England: Edward Arnold Publishers Ltd, 1922. Digital file made available by Science History Institute, at https://digital.sciencehistory.org/works/79407z32j, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2976526

By The original uploader was Den fjättrade ankan at Swedish Wikipedia. - Källa:Dmitrij Ivanovitj Mendelejev (1834 - 1907). Originally from sv.wikipedia; description page is/was here., Public Domain, https://commons.wikimedia.org/w/index.php?curid=1574857

James Chadwick Photo, https://commons.wikimedia.org/wiki/File:Groves_and_Chadwick_830308.tif: Unless otherwise indicated, this information has been authored by an employee or employees of the Los Alamos National Security, LLC (LANS), operator of the Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396 with the U.S. Department of Energy. The U.S. Government has rights to use, reproduce, and distribute this information. The public may copy and use this information without charge, provided that this Notice and any statement of authorship are reproduced on all copies. Neither the Government nor LANS makes any warranty, express or implied, or assumes any liability or responsibility for the use of this information.

Periodic Table used with permission from https://sciencenotes.org/printable-periodic-table/

Music:

Music by Anastasia Chubarova from https://pixabay.com https://pixabay.com/users/music_for_videos-26992513/?utm_source=link-attribution&utm_medium=referral&utm_campaign=music&utm_content=161569


Early Mass Spec (Mass Spectrograph) Experiments
/youtube/video/qPm051Qo8s0?t=0
Puzzle of Neon's 2 Masses
/youtube/video/qPm051Qo8s0?t=130
What We Already Knew About Atomic Structure
/youtube/video/qPm051Qo8s0?t=167
Mysterious Gamma Radiation
/youtube/video/qPm051Qo8s0?t=198
Chadwick's Experimental Set-Up
/youtube/video/qPm051Qo8s0?t=266
Discovery of the Neutron
/youtube/video/qPm051Qo8s0?t=395
Neon's 2 Masses Explained
/youtube/video/qPm051Qo8s0?t=440
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