Noun

(en noun)

(history of science) A hypothetical particle posited by Greek philosophers as an ultimate and indivisible component of matter.

(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.

* {{quote-magazine, year=2013, month=September-October, author= Katie L. Burke

, magazine=(American Scientist), title= In the News , passage=Oxygen levels on Earth skyrocketed 2.4 billion years ago, when cyanobacteria evolved photosynthesis:

A mote of dust in a sunbeam.

The smallest, indivisible constituent part or unit of something. (Now generally interpreted as a figurative use of the physics sense, above.)

* 1835 , Sir , Sir (James Clark Ross), Narrative of a Second Voyage in Search of a North-west Passage …'', Volume 1 , pp.284-5

Towards the following morning, the thermometer fell to 5°; and at daylight, there was not an atom of water to be seen in any direction.

A very small amount (of something immaterial); a whit.

* 1873 , (Isabella Macdonald Alden) (as "Pansy"), Three People , Western Tract and Book Society (1873), page 325:

"I have hardly the faintest atom of hope," answered this honest, earnest man.

*

those of us who are capable of it are forced to work to the last atom of our strength

(mathematics) A non-zero member of a (Boolean algebra) that is not a union of any other elements.

(computing, programming, Lisp) An individual number or symbol, as opposed to a list. A scalar value.

Noun

(en noun)

(chemistry) An cation, consisting of a large cluster of atoms, in which the positive charge is spread over many atoms