Evolution of the Atomic Theory: from 400 B.C to late-20th century

Nazli Suyolcu9D – Hisar Okullari

Timeline for the Atomic Theories

Democritus- 442 B.C.

Lavoisier-1789

Proust-1799

Dalton-1803 Faraday-1832

Stoney-1894

Thomson-1897

Rutherford-1898

Bohr-1922

Milikan-1909 Chadwick-

1932

Descriptions of the Atomic Theories

Democritus (460 B.C.-375 B.C.)

Atomus=indivisibleEvery matter is composed of constantly moving invisible particles called atomsIndestructible, solid, different for any particular matter

Solids -> small pointy Liquids-> large, round

Antoine Laurent Lavoisier (1743-

1794) “Father of Modern Chemistry”

By evaporating and condensing rain water and weighing the solid residue, he found The Law of Conservation of Masses.Clarified the notion of elements being indivisible even by chemical analysisHe added 11 more elements to the Periodic tableHe developed the first compound nomenclature after their consisting elements which is still in use.

Joseph Proust (1754 – 1826)

He experimented with Hydrogen Sulfide by using it as a reagent and noted his observations and data

He found the Law of Definite Proportions: every compound is made up of elements in the same particular ratio which built the base of stoichiometry

John Dalton (1766-1844)

He made additions to Democritus’ theory:Compounds are hard to break into its elements

It’s called The Billiard Model

Different elements consist of different atoms

“Atoms can be neither created nor destroyed.”

Michael Faraday (1791-1867)

Faraday split molecules with electricity what he called “electrolysis” and later Laws of Electrolysis

He got the idea that atoms had an electrical parts in them (later on which got called electrons)

George J. Stoney (1826-1911)

He introduced the term electron as a subparticle ->Dalton’s theory got disproved

J.J.Thomson (1856-1940)

He found the so called ‘electron’ by showing the negatively charged particles in cathode rays.

He invented the Plum Pudding Model:The atom is positively charged (pudding)

It contains electrons in it (plums)

This model also explained the atom electroneutrality

Ernest Rutherford (1871-1937)

He proposed the Nuclear Model by doing his known Gold Foil experiment. The atom has:

a dens +-charged nucleus (proton)

Multiple very-small electrons orbit the nucleus

Niels Bohr (1885-1962)Bohr discovered the Planetary Model:

The nucleus is surrounded by electrons on orbitals having different energy levels

The orbitals have integer numbers (n)

The orbitals are circular and have different radii

This is the introduction to ‘Quantum’ in chemistry

Robert A. Millikan (1868-1953 Millikan worked on oil droplets and ionized air to observe electrons. He found out that:

Electrons had a charge of and integral multiple of 1.59 x 10-19 C (Planck’s constant)

It’s mass is at least 1000 times smaller than the whole atom.

James Chadwick 1891-1974

He discovered the neutron(neutral particles) by using the data from Marie Curie’s hydrogen experiment.

Neutrons and protons have the same mass

In short, the models mentioned throughout the presentation are..

SourcesTOUPADAKIS, Andreas, Chemistry Reader 2A

http://pages.uoregon.edu/ch111/L5.htm

http://science.howstuffworks.com/dictionary/famous-scientists/chemists/joseph-louis-proust-info.htm

http://www.livescience.com/32016-niels-bohr-atomic-theory.html

http://www.chalkbored.com/lessons/chemistry-11/atomic-models-handout.pdf

https://prezi.com/esib9acdwyva/atomic-structure-timeline/