Atoms and Compounds

1. Atoms and Compounds Dalton’s Atomic Theory

2. 3.2Atoms and Compounds • 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. • Atom – smallest particle of an element that retains the chemical identity of that element.

3. 3.2 Atoms and Compounds 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.

4. 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

5. Dalton’s Atomic Theory This can be explained in terms of atoms. Compound 1: CO (Carbon monoxide) Compound 2: CO2 (Carbon dioxide) Law of Multiple Proportions When 2 or more elements form a series of compounds, the ratios of the masses of elements can be reduced to small whole #’s

6. Dalton’s Atomic Theory • Each element is made up of tiny particles called atoms. • The atoms of a given element are identical; the atoms of different elements are different in some fundamental way • Chemical compounds are formed when atoms of different elements combine with each other. A given compound always has the same relative numbers and types of atoms • Chemical reactions involve reorganization of the atoms – changes in the way they are bound together. Atoms are not changed, created, or destroyed in a chemical reaction.