4.1. Atoms http://www.ck12.org
4.1 Atoms
Lesson Objectives
- Explain the law of conservation of mass, the law of definite proportions, and the law of multiple proportions.
- Describe John Dalton’s atomic theory.
Lesson Vocabulary
- atom
- law of conservation of mass
- law of definite proportions
- law of multiple proportions
Early Atomic Models
Democritus was a Greek philosopher who lived from 460 B.C. until 370 B.C. He was among the first known
individuals to suggest the idea of the atom as the basic unit of matter. The word atom comes from the Greek
wordatomos, meaning “indivisible.” Democritus (Figure4.1) was indeed ahead of his time, but his ideas were not
useful at that time in describing chemical behavior because there was no experimental evidence to support it. His
approach was a philosophical one rather than a truly scientific one. Many centuries would pass before the notion of
atoms was merged with modern scientific experimentation and thought.
FIGURE 4.1
Democritus believed that all matter consisted of tiny, indestructible parti-
cles called atoms.