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 Symbols of Elements, Their Atomic Number and Mass Number https://www.khanacademy.org/science/cambridge-o-level-physics-cie/x0e04e0cb682fb793:nuclear-physics/x0e04e0cb682fb793:the-atom/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 Symbols of Elements, Their Atomic Number and Mass Number 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/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