Atoms: The Building Blocks of Matter

The Atom: From Philosophical Idea to Scientific Theory

Opinion or Theory?

Young people should not smoke.

Smoking at an early age may make it more difficult to quit smoking later.

Early Views of Matter• Democritus (450 B.C.) – proposed that matter

was not infinitely divisible; that matter could be broken down into tiny particles, which were not divisible.

• These particles were referred to as atomos.

• Aristotle (~400 B.C.) – believed that matter was continuous.

Foundations of Atomic Theory• Antoine Lavoisier – (late 1700’s) used a balance to

show that matter was not created or destroyed during chemical reactions – Law of Conservation of Matter (Mass).

• Joseph Proust (1799)- showed that compounds always contain exactly the same proportion of elements by mass– Law of constant composition

a.k.a. Law of definite proportion

For example: The mass of water (H2O) always contains exactly 88.9 % oxygen and 11.1 % hydrogen.

Dalton’s Atomic Theory• John Dalton – (early 1800’s) proposed the

atomic theory of matter

• Compound 2 has exactly twice as much oxygen as Compound 1

Mass of oxygen that combines with 1 gram of Carbon

Compound 1 1.33 g

Compound 2 2.66 g

Dalton’s Atomic TheoryThis can be explained in terms of atoms.

Compound 1: CO (Carbon monoxide)

Compound 2: CO2 (Carbon dioxide)

Law of Multiple Proportions

If 2 or more elements form a series of compounds, the ratios of the masses of elements can be reduced to small whole #’s

Dalton’s Atomic Theory1. Matter is composed of tiny particles called atoms.

2. Atoms of a given element are identical in size, mass, and properties. Atoms of different elements are fundamentally different.

3. Atoms cannot be divided, created, or destroyed.

4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds.

5. In chemical reactions, atoms are combined, separated, or rearranged.