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Courses on Khan Academy are always 100% free. Start practicing—and saving your progress—now! https://www.khanacademy.org/science/hs-chemistry/x2613d8165d88df5e:atoms-elements-and-the-periodic-table/x2613d8165d88df5e:atomic-structure/v/elements-and-atomic-number

Want to explore more? Check out the full Atoms, isotopes, and ions playlist here: https://youtube.com/playlist?list=PLSQl0a2vh4HBSf5CVmr7BQ-DAayIsE71N&si=n5y_agsm1Gc3CdM-

Atoms come in a variety of types, called elements, each with a unique set of physical and chemical properties. An element is defined by the number of protons in its atoms, known as its atomic number. The periodic table organizes the elements by atomic number and provides other key information about them such as their names and chemical symbols.

Sections:
00:00 - What are elements?
00:32 - Atomic number and protons
01:03 - Electrons in neutral atoms
01:33 - Introduction to the periodic table
01:59 - Chemical symbols of elements
02:45 - Understanding an element's box
03:34 - Using the periodic table
03:36 - Example: Phosphorus
03:55 - Example: Mercury
04:16 - Conclusion: Elements in the universe

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Credits:
“Galaxy Cluster Abell 2218” by NASA, licensed under a Creative Commons Attribution License (CC BY 2.0):
https://www.flickr.com/photos/144614754@N02/45981024214/
https://creativecommons.org/licenses/by/2.0/

“Liquid oxygen in a beaker (cropped and retouched)” by Nika Glover [Public domain], accessed via Wikimedia Commons:
https://commons.wikimedia.org/wiki/File:Liquid_oxygen_in_a_beaker_(cropped_and_retouched).jpg

“Oxygen Tanks” by Todd Van Hoosear, licensed under a Creative Commons Attribution License (CC BY-SA 2.0):
https://www.flickr.com/photos/92787319@N00/7557054698
https://creativecommons.org/licenses/by-sa/2.0/

“Graphite-and-diamond-with-scale” by Robert M. Lavinsky, licensed under a Creative Commons Attribution License (CC BY-SA 3.0):
https://commons.wikimedia.org/wiki/File:Graphite-and-diamond-with-scale.jpg
https://creativecommons.org/licenses/by-sa/3.0/deed.en

“Gold nugget (placer gold) 1 (17001285916)” by James St. John, licensed under a Creative Commons Attribution License (CC BY 2.0):
https://commons.wikimedia.org/wiki/File:Gold_nugget_(placer_gold)_1_(17001285916).jpg
https://creativecommons.org/licenses/by/2.0/deed.en

“Gold necklace with coin pendants MET DP107044” by the Metropolitan Museum of Art [Public domain], accessed via Wikimedia Commons:
https://commons.wikimedia.org/wiki/File:Gold_necklace_with_coin_pendants_MET_DP107044.jpg

“Bismuth crystal macro” by Dschwen, licensed under a Creative Commons Attribution License (CC BY-SA 3.0):
https://commons.wikimedia.org/wiki/File:Bismuth_crystal_macro.jpg
https://creativecommons.org/licenses/by-sa/3.0/deed.en

“Xenon-glow” by Jurii, licensed under a Creative Commons Attribution License (CC BY 3.0):
https://commons.wikimedia.org/wiki/File:Xenon-glow.jpg
https://creativecommons.org/licenses/by/3.0/deed.en

“Osmium crystals (cropped)” by Alchemist-hp, licensed under a Free Art License (FAL 1.3):
https://commons.wikimedia.org/wiki/File:Osmium_crystals_(cropped).jpg
http://artlibre.org/licence/lal/en/

“Congrats bqt” by Pioneer Balloon Company [Public domain], accessed via Wikimedia Commons:
https://commons.wikimedia.org/wiki/File:Congrats_bqt.jpg

“Iron electrolytic and 1cm3 cube” by Alchemist-hp, licensed under a Creative Commons Attribution License (CC BY-NC-ND 3.0):
https://commons.wikimedia.org/wiki/File:Iron_electrolytic_and_1cm3_cube.jpg
https://creativecommons.org/licenses/by-nc-nd/3.0/