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 Compounds
Important 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 matter
Mass 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 Theory
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 Theory
Dalton’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.
H2 O
Subscript of one
is not included.
# of H atoms
Element Symbols