atomic theory

noun

1

: a theory of the nature of matter: all material substances are composed of minute particles or atoms of a comparatively small number of kinds and all the atoms of the same kind are uniform in size, weight, and other properties

2

: any of several theories of the structure of the atom

especially : one based on experimentation and theoretical considerations holding that the atom is composed essentially of a small positively charged comparatively heavy nucleus surrounded by a comparatively large arrangement of electrons

Examples of atomic theory in a Sentence

Recent Examples on the Web

The most famous text influenced by Democritus is De rerum natura (On the Nature of Things), the didactic poem in six books by Titus Lucretius Carus (99 BCE–55 BCE), a poet of the late Roman Republic and a follower of the Greek philosopher Epicurus, who had taken up Democritus’s atomic theory. —Priyamvada Natarajan, The New York Review of Books, 15 June 2021

The sprawling tale begins in ancient Greece, with the origin of atomic theory. —Alex Orlando, Discover Magazine, 16 May 2021

Before atomic theory—which states that all matter is made up of tiny particles called atoms—people didn’t have a good idea of what matter really was. —Caroline Delbert, Popular Mechanics, 24 Feb. 2022

But Rovelli says that the degree of confirmation of atomic theory shouldn’t even be measured in the same units as that of string theory. —Quanta Magazine, 16 Dec. 2015

String theory is not, say, 10 percent as confirmed as atomic theory; the two have different statuses entirely. —Quanta Magazine, 16 Dec. 2015

Word History

First Known Use

1738, in the meaning defined at sense 1

Kids Definition

atomic theory

noun

1

: a theory of the nature of matter: all material substances consist of very tiny particles or atoms of not really many kinds and all the atoms of the same kind are uniform in size, weight, and other properties

2

: any of several theories of the structure of the atom

especially : one saying that the atom consists essentially of a small positively charged heavy nucleus in relation to a large arrangement of electrons that surround the nucleus

Medical Definition

atomic theory

noun

1

: a theory of the nature of matter: all material substances are composed of minute particles or atoms of a comparatively small number of kinds and all the atoms of the same kind are uniform in size, weight, and other properties

called also atomic hypothesis

2

: any of several theories of the structure of the atom

especially : one based on experimentation and theoretical considerations holding that the atom is composed essentially of a small positively charged comparatively heavy nucleus surrounded by a comparatively large arrangement of electrons