Atomic Structure. Chapter 4 Lesson 1. Early Models of the Atom. First: A definition: An atom is the smallest particle of an element that retains its identity in a chemical reaction. (p101). Early Models of the Atom. Democritis (before 370 BC): Atoms are indivisible
What happens to atoms in a chemical reaction according to Dalton’s Theory?
2.4 x 1022 atoms (the human population in the universe is 6 x 109 people