https://www.khanacademy.org/science/grade-11-chemistry-snc-aligned/x203b0fc81a964b2d:atomic-structure/x203b0fc81a964b2d:untitled-83/v/introduction-to-the-atom 2021-03-18T10:33:22Z Introduction to the atom Learn how atoms are made up of protons, neutrons, and electrons. Elements are defined by the atomic number, the number of protons in the nucleus. The mass of an atom is determined by the total number of protons and neutrons.  Sal Khan video https://cdn.kastatic.org/googleusercontent/Njmwm-XqkUEUaIUunvEoRCwM2nvwARZsykcUj2_FxWGG2qNU7u245UgzKsRdWANkgHALQB0iqj0Q3YGllGSQpOBN Introduction to the atom Learn how atoms are made up of protons, neutrons, and electrons. Elements are defined by the atomic number, the number of protons in the nucleus. The mass of an atom is determined by the total number of protons and neutrons.  https://cdn.kastatic.org/ka-youtube-converted/1xSQlwWGT8M.mp4/1xSQlwWGT8M.mp4 1265 Atomic structure https://www.khanacademy.org/science/hs-chemistry/x2613d8165d88df5e:atoms-isotopes-and-ions/x2613d8165d88df5e:atomic-structure/v/protons-neutrons-and-electrons-in-atoms 2025-11-01T06:31:04.963641538Z Protons, neutrons, and electrons in atoms Atoms are made up of three types of subatomic particles: protons, neutrons, and electrons. Protons and neutrons are found in the nucleus, the dense region at the center of an atom. Electrons are found outside the nucleus. Protons are positively charged and have a mass of about 1 u. Neutrons are neutral (have no charge) and also have a mass of about 1 u. Electrons are negatively charged and have a much smaller mass of about 0.0005 u. Wieteke Holthuijzen video https://cdn.kastatic.org/ka_thumbnails_cache/b0e49086-7776-4d8b-8b13-7afbfd62b856_1280_720_base.png Protons, neutrons, and electrons in atoms Atoms are made up of three types of subatomic particles: protons, neutrons, and electrons. Protons and neutrons are found in the nucleus, the dense region at the center of an atom. Electrons are found outside the nucleus. Protons are positively charged and have a mass of about 1 u. Neutrons are neutral (have no charge) and also have a mass of about 1 u. Electrons are negatively charged and have a much smaller mass of about 0.0005 u. https://cdn.kastatic.org/ka-youtube-converted/lz_gMkQr7YE.mp4/lz_gMkQr7YE.mp4 151 Atomic structure https://www.khanacademy.org/science/hs-chemistry/x2613d8165d88df5e:atoms-isotopes-and-ions/x2613d8165d88df5e:atomic-structure/e/understand-atomic-structure 2026-04-07T22:59:30.107127435Z Understand: atomic structure Check your understanding of atomic structure in this set of free practice questions. Megan Cohn exercise https://www.khanacademy.org/science/mh-grade-8-science/x0f256b8de9c7cf34:inside-the-atom/x0f256b8de9c7cf34:atomic-number-and-mass-number/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 structure https://www.khanacademy.org/science/biology/history-of-life-on-earth/radiometric-dating/a/atomic-number-atomic-mass-and-isotopes-article 2021-04-29T07:51:16Z Atomic number, atomic mass, and isotopes Fundamental properties of atoms including atomic number and atomic mass. The atomic number is the number of protons in an atom, and isotopes have the same atomic number but differ in the number of neutrons. article https://www.khanacademy.org/science/mh-grade-8-science/x0f256b8de9c7cf34:inside-the-atom/x0f256b8de9c7cf34:atomic-number-and-mass-number/e/lo-2-3-atomic-number-and-mass-number 2025-08-05T18:56:35.058002345Z Atomic number and mass number Let's solve some problems to better understand atomic and mass numbers. Aakash Bagga exercise