Download Introduction to Atomic Theory

Applied Chemistry
Mr. Gensits
Class Notes: September 30, 2014
Matter Is Made Up of Atoms
Introduction to Atomic Theory
Some early Greek philosophers believed that there were four
elements: air, earth, fire, and water.
Democritus
(4th Century B.C.)
Suggested the existence of tiny indestructible particles
(atoms) that made up all matter
Development of the Modern Atomic Theory
Lavoisier (1782)
Noted that the masses of the reactants before a chemical
reaction was equal to the masses of the products after the
reaction was completed.
This became known as the Law of Conservation of Matter
(Mass)
Joseph Proust (1799)
Observed that the composition of water was always 11%
hydrogen and 89% oxygen.
Law of Definite Composition
The elements that compose a compound are always in a
certain percentage by mass.
John Dalton –first formulated the main principles of modern
atomic theory
Dalton’s Atomic Theory (1803)
1. All elements are composed of tiny indivisible particles
called atoms.
2. Atoms of the same element are identical. The atoms of
any one element are different from those of any other
element.
3. Atoms of different elements can combine with one another
in single whole number ratios to form compounds.
4. Chemical reactions occur when atoms are separated,
joined, or rearranged.
Atomic Particles
Electrons
negatively charged particles
discovered first (1897) by J. J. Thomson
travels around the nucleus
found in the electron cloud
Nucleus - central part of the atom
discovered in 1911 by Ernest Rutherford
Protons
positively charged
discovered 1918 (Rutherford)?
1840 times more massive than electron
found in the nucleus
it is believed that protons are composed
of three smaller particles called quarks
Neutrons
Have no charge.
discovered in 1932 by James Chadwick
in the nucleus
it is believed that a neutron is also composed of three quarks
Review of Atomic Models
Dalton Model
Thomson Model
Rutherford Model