atom: Quick Facts

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Nov. 8, 2026

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Photos and Videos

Bohr model diagram of a hydrogen atom showing a green nucleus labeled H, a single electron orbit, and text with atomic mass 1.008 and electron configuration 1.

Diagram of the shell atomic model for a neon atom, showing electrons orbiting in two shells around a central nucleus. An inset details the nucleus, depicting clustered protons and neutrons.

isotopes of hydrogen

Diagram of the Millikan oil-drop experiment showing a chamber with oil droplets sprayed from an atomizer, falling between two charged metal plates. A light source and viewing microscope are used to observe the droplets, which are influenced by electric and ionizing radiation to measure their charge.

Diagram of the Bohr atomic model showing an electron moving in circular orbits with quantized energy levels around a central nucleus, alongside an energy level diagram illustrating electron transitions.

A diagram showing atomic energy levels and electron orbitals, with labeled boxes for s, p, d, and f orbitals from levels 1 to 7, and arrows indicating the order of electron filling. Some higher orbitals are shaded to show they are not occupied by ground-state electrons.

Diagram of the periodic table with each element's position marked by boxes and labeled with electron subshells, using arrows to indicate the order in which valence shells fill with electrons.

Diagram showing the formation of an ionic bond between sodium (Na) and chlorine (Cl) atoms. Sodium loses an electron to become Na+, chlorine gains an electron to become Cl-, resulting in sodium chloride (NaCl), or table salt.

Diagram showing the formation of a polar covalent bond in a water molecule, with two hydrogen atoms bonding to one oxygen atom to form H2O, illustrating shared electrons and chemical reaction.

A scientific graph plots average nuclear binding energy per nucleon (in MeV) against atomic mass number, showing a sharp rise at low mass numbers, peaking near iron (Fe), then gradually declining for heavier elements. Key isotopes are labeled along the curve.

Illustration of an atom showing a central nucleus with multiple electrons orbiting in concentric shells, representing electron arrangement in atoms.

The Structure of an Atom Explained

Robert Millikan's method for measuring the charge of an electron

Fission of a uranium nucleus by a neutron

How scientists discovered atoms

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Topics

subatomic particle particle radiation allotrope atomic nucleus line spectrum atomic particle radioactivity Atomism isotope periodic table Star Universe Planet molecule Astronomy radiation chemical bonding principles of physical science electricity liquid

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Key People

Ernest Rutherford

Ernest Rutherford

British physicist

Neils Bohr

Niels Bohr

Danish physicist

Lev Davidovich Landau

Lev Davidovich Landau

Russian physicist

Steven Chu.

Steven Chu

American physicist

Phillips, William D.

William D. Phillips

American physicist

Kastler, 1966

Alfred Kastler

French physicist

Condon, Edward U.

Edward U. Condon

American physicist

Claude Cohen-Tannoudji, 2007

Claude Cohen-Tannoudji

French physicist

Periodic Table of the elements concept image (chemistry)

Facts You Should Know: The Periodic Table Quiz