Chemical Foundations: Elements, Atoms, and

Ions

Atoms & Compounds

Atoms and Compounds

Objectives: • Students will be able to identify 4 parts of Dalton’s

Atomic Theory.• Students will be able to write and interpret chemical

compound formulas

Atoms and CompoundsImportant milestones in the development of modern

atomic theory:

 • Democritus (450 BC)

• Proposed that matter was not infinitely divisible• Matter could be broken down into tiny particles he

called atomos.

Atoms and Compounds• Antoine Lavoisier (late 1700’s)

• Proposed the Law of Conservation of Matter• Matter is not created or destroyed during

chemical reactions

• Joseph Proust (1799)• Proposed the Law of constant composition• A given compound always contains the same

elements in the same proportions by mass• 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 matterMass of oxygen that

combines with 1 gram of Carbon

Compound 1 1.33 g

Compound 2 2.66 g

This can be explained in terms of atoms.

Compound 1: CO (Carbon monoxide)Compound 2: CO2 (Carbon dioxide)

Dalton’s Atomic TheoryLaw 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 TheoryDalton’s Atomic Theory (early 1800’s)• Elements are made up of tiny particles called atoms.• Atoms of a given element are identical. Atoms of

different elements are different in some fundamental way.

• Chemical compounds from when different elements combine. A given compound always contains the same elements in the same proportions.

• Chemical reactions involve reorganization of atoms. Atoms are not created or destroyed in chemical reactions.

 

Formulas of Compounds

Compound- combination of two or more elements in a fixed proportion.

H2O

Element Symbols

# of H atoms

Subscript of one is not included.