https://www.khanacademy.org/science/hs-chemistry/x2613d8165d88df5e:atoms-isotopes-and-ions/x2613d8165d88df5e:atomic-structure/v/elements-and-atomic-number 2025-12-03T14:30:51.007256483Z Elements and atomic number 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. Wieteke Holthuijzen video https://cdn.kastatic.org/ka_thumbnails_cache/f9b78e3a-4de0-46ed-a0cb-3e36d84fa21b_1280_720_base.png Elements and atomic number 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. https://cdn.kastatic.org/ka-youtube-converted/OQi8FwPSu5o.mp4/OQi8FwPSu5o.mp4 274 Atomic number and atomic mass https://www.khanacademy.org/science/cambridge-o-level-chemistry-cie/x8bc8fb44369617ed:atoms-elements-and-compounds/x8bc8fb44369617ed:atomic-structure-and-the-periodic-table/v/atomic-number-mass-number-and-isotopes-ur 2025-08-08T00:24:37.843818748Z Atomic number, mass number Created by Khan Academy video https://cdn.kastatic.org/googleusercontent/ZCdwTudJg6e6n-P2gsaUborP4izvMsGo71pvEVlX9dNYWcLXcP7VHkWpn2grt4TUP1KoJLQP9NswyHBuBLSFTBw Atomic number, mass number Created by Khan Academy https://cdn.kastatic.org/ka-youtube-converted/-F0KbgYuyhI.mp4/-F0KbgYuyhI.mp4 432 Atomic number and atomic mass https://www.khanacademy.org/science/bridge-course-class-11th-chemistry/x426c9d2c554669cb:basic-concepts-of-chemistry/x426c9d2c554669cb:structure-of-an-atom/e/atomic-and-mass-number 2023-08-13T07:34:46.711956309Z Atomic and mass number Let's solve some questions! vibhor exercise https://www.khanacademy.org/science/cambridge-o-level-chemistry-cie/x8bc8fb44369617ed:atoms-elements-and-compounds/x8bc8fb44369617ed:isotopes/v/atomic-number-mass-number-and-isotopes 2021-03-23T09:46:01Z Atomic number, mass number, and isotopes Each atom has a charged sub-structure consisting of a nucleus, which is made of protons and neutrons, surrounded by electrons. The number of protons and the mass number of an atom define the type of atom. Atoms of the same element with different mass numbers are called isotopes.  Jay video https://cdn.kastatic.org/googleusercontent/m8DpxjtEI4cOeDd6Gev17fgG0-R-_Dir4VamMrT-s7rq9Wq9o0yQ7b9BfwIJHrXVykAe-uwgygdKTkvsUuu6lLXfhQ Atomic number, mass number, and isotopes Each atom has a charged sub-structure consisting of a nucleus, which is made of protons and neutrons, surrounded by electrons. The number of protons and the mass number of an atom define the type of atom. Atoms of the same element with different mass numbers are called isotopes.  https://cdn.kastatic.org/ka-youtube-converted/I-Or4bUAIfo.mp4/I-Or4bUAIfo.mp4 584 Atomic number and atomic mass https://www.khanacademy.org/science/hs-chemistry/x2613d8165d88df5e:atoms-isotopes-and-ions/x2613d8165d88df5e:isotopes-and-ions/v/worked-example-using-the-mass-number-equation 2025-12-03T14:30:51.007256483Z Worked example: using the mass number equation The sum of the number of neutrons and protons in an atom is called its mass number. If we know the mass number of an atom, we can determine the number of neutrons in its nucleus. Wieteke Holthuijzen video https://cdn.kastatic.org/ka_thumbnails_cache/6e21f6d7-2d25-4628-866c-a2a94729826f_1280_720_base.png Worked example: using the mass number equation The sum of the number of neutrons and protons in an atom is called its mass number. If we know the mass number of an atom, we can determine the number of neutrons in its nucleus. https://cdn.kastatic.org/ka-youtube-converted/T9UH12HdFdo.mp4/T9UH12HdFdo.mp4 121 Atomic number and atomic mass https://www.khanacademy.org/science/cambridge-o-level-chemistry-cie/x8bc8fb44369617ed:atoms-elements-and-compounds/x8bc8fb44369617ed:atomic-structure-and-the-periodic-table/e/lo-2-3-atomic-number-and-mass-number 2026-04-28T11:00:37.315336883Z Atomic number and mass number Let's solve some problems to better understand atomic and mass numbers. Aakash Bagga exercise https://www.khanacademy.org/science/hs-chemistry/x2613d8165d88df5e:atoms-isotopes-and-ions/x2613d8165d88df5e:atomic-structure/e/understand-atomic-structure 2026-04-26T16:30:39.382257956Z Understand: Atomic structure Check your understanding of atomic structure in this set of free practice questions. Megan Cohn exercise https://www.khanacademy.org/science/hs-chemistry/x2613d8165d88df5e:atoms-isotopes-and-ions/x2613d8165d88df5e:atomic-structure/e/apply-atomic-structure 2026-04-26T16:30:39.382257956Z Apply: Atomic structure Apply your understanding of atomic structure in this set of free practice questions. Megan Cohn exercise https://www.khanacademy.org/science/cambridge-o-level-chemistry-cie/x8bc8fb44369617ed:atoms-elements-and-compounds/x8bc8fb44369617ed:elements-compounds-and-mixtures/e/apply-elements-and-atoms 2025-12-18T18:00:52.364814749Z Apply: elements and atoms Apply your understanding of elements and atoms in this set of free, standards-aligned practice questions. donna exercise