atom

atom — noun

1. the basic unit in chemistry that keeps the character of one element and may join

1.nounB2
Definition

the basic unit in chemistry that keeps the character of one element and may join to other units

Example

A hydrogen atom has only one electron around its center.

pattern: an atom of [element]

In the model, each carbon atom touched four small white balls.

collocation: carbon atom

Common collocations
  • hydrogen atom
  • carbon atom
  • split an atom
  • atomic structure
  • lose an electron
Synonyms
  • particle

    broader scientific word that can refer to many kinds of very small pieces

  • unit

    very general and does not specifically suggest chemistry

  • building block

    an explanatory phrase rather than a precise scientific term

Grammar Patterns

an atom of hydrogen

atoms combine to form molecules

an atom loses an electron

Usage Note

Common in chemistry and physics. Distinguish from noun/2 TINY AMOUNT, which means a very small piece or quantity. Also distinguish atom from molecule: a molecule is made from two or more atoms joined together.

Common Mistakes

Water has three atoms in one atom.
Water has three atoms in one molecule.
an atom is one unit of an element; a molecule is a group of atoms joined together.

2. a very small piece or amount of something

2.noun
Definition

a very small piece or amount of something

Example

There was not an atom of sugar left in the tea.

not an atom of + noun

Without an atom of shame, the thief asked for more money.

without an atom of + abstract noun

Common collocations
  • not an atom of
  • every atom of
  • an atom of dust
  • an atom of fear
  • an atom of sugar
Synonyms
  • bit

    the most general everyday word for a small amount or piece

  • speck

    usually a tiny visible mark or grain, especially of dust or dirt

  • trace

    often means a very small amount that is just enough to notice

  • particle

    can sound more scientific or formal than everyday bit

Grammar Patterns

an atom of dust

not an atom of pity

every atom of something

Usage Note

Usually appears with of, especially in phrases such as not an atom of, without an atom of, or every atom of. It is much less common than ordinary words like bit, speck, or trace.

Common Mistakes

There wasn't atom of milk in the cup.
There wasn't an atom of milk in the cup.
use an before atom in this pattern.

Word family

Synonym discussion

Sense: noun/1

For this science sense, atom means one basic unit of an element, such as one hydrogen atom or one gold atom. Molecule is different: it is a group of atoms joined together, like a water molecule. Element names the substance itself, not one single unit of it, so oxygen is an element but one oxygen atom is a single atom. Particle is broader and can mean any very small piece in science, so it is less exact than atom. Use atom when you want the chemistry meaning precisely. You can say Each water molecule contains hydrogen atoms, but not Each water atom contains hydrogen atoms.

atom ↗molecule ↗element ↗particle ↗

Etymology

GreekLatinFrenchEnglish

Atom came into English through Latin and French from Greek atomos, a word meaning not cut or indivisible. People first used it for the idea of the smallest possible piece of matter, and modern science later kept the word for the basic unit of an element.