Atom definition

ătəm
Frequency:
The smallest unit of an element, consisting of at least one proton and (for all elements except hydrogen) one or more neutrons in a dense central nucleus, surrounded by one or more shells of electrons. In electrically neutral atoms, the number of protons equals the number of electrons. Atoms remain intact in chemical reactions except for the removal, transfer, or exchange of certain electrons.
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(obs.) Any of the indivisible particles postulated by philosophers as the basic component of all matter.
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The smallest, indivisible constituent part or unit of something. (Now generally interpreted as a figurative use of the physics sense, above.) [from 17th c.]
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The smallest unit of an element, having all the characteristics of that element and consisting of a very small and dense central nucleus containing protons and neutrons, surrounded by one or more shells of orbiting electrons. Atoms remain undivided in chemical reactions except for the donation, acceptance, or exchange of valence electrons.
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The irreducible, indestructible material unit postulated by ancient atomism.
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This unit regarded as a source of nuclear energy.
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(history of science) A hypothetical particle posited by Greek philosophers as an ultimate and indivisible component of matter. [from 15th c.]
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A very small amount (of something immaterial); a whit. [from 17th c.]
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(mathematics) A non-zero member of a Boolean algebra that is not a union of any other elements. [from 20th c.]
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(computing, programming, Lisp) An individual number or symbol, as opposed to a list. A scalar value.
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(chem., physics) Any of the smallest particles of an element that combine with similar particles of other elements to produce compounds: atoms combine to form molecules, and consist of a complex arrangement of electrons revolving about a positively charged nucleus containing (except for hydrogen) protons and neutrons and other particles.
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An atom includes a nucleus, and then a series of orbital circles that surround this nucleus similar to the solar system structure.
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The protons and the neutrons reside in the nucleus.
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The electrons are in the orbitals.
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The amount of protons in the nucleus of an atom determines its atomic number.

Hydrogen and helium are examples of elements that have an atom.

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An extremely small part, quantity, or amount.
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A part or particle considered to be an irreducible constituent of a specified system.
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(now historical) The smallest medieval unit of time, equal to fifteen ninety-fourths of a second. [from 10th c.]
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(physics, chemistry) The smallest possible amount of matter which still retains its identity as a chemical element, now known to consist of a nucleus surrounded by electrons. [from 16th c.]

A molecule is a close combination of atoms.

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A mote of dust in a sunbeam. [from 16th c.]
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A tiny particle of anything; jot.
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The definition of an atom is the smallest component of an element, characterized by a sharing of the chemical properties of the element and a nucleus with neutrons, protons and electrons.
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the atom
  • nuclear energy
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Other Word Forms

Noun

Singular:
atom
Plural:
atoms

Idioms and Phrasal Verbs

the atom

Origin of atom

  • Middle English attome from Latin atomus from Greek atomos indivisible, atom a- not a–1 tomos cutting (from temnein to cut tem- in Indo-European roots)

    From American Heritage Dictionary of the English Language, 5th Edition

  • From Middle French atome, from Latin atomus (“smallest particle”), from Ancient Greek ἄτομος (atomos, “indivisible”), from ἀ- (a-, “not”) + τέμνω (temnō, “I cut”).

    From Wiktionary