History of the Atom Picture Timeline By Enrique Martinez

Aristotle

340

• Suggested that matter was made up of atoms, and that it will always exist
• Developed methods for gathering scientific facts; which other scientists used as an example/ guide for all scientific work

Aristotle atom model

340

Democritus atom model

440

Democritus

440

• Beleived that if you kept cutting a substance in half, you would eventually reach an uncuttable part he called particles
• Suggested that atoms were hard & small particles that were put together into a particular shape, also thought that they were always moving and combine w/ each other
• stated that the universe is made up of empty space & an infinite number of particles

Antoine Lavoisier

Oct 13, 1777

• His experiments led to 1 of the fundamental laws of chemical behavior; law of conservation of matter; matter is conserved in a chemical reaction
• B/c of this we now understand why atoms are neither created or destroyed in a chemical reaction

John Dalton

Oct 13, 1803

• Formed Atomic theory: states that all matter is made up of invisible particles called atoms; couldn't be destroyed
• Also said that even though atoms of an element are the same; different elements had different sized atoms and masses

John Dalton atom model

Oct 13, 1803

Henri Becquerel

Oct 13, 1896

• Accidentally discovered that some atoms are radioactive

Henri Becquerel atom model

Oct 13, 1896

J. J. Thomson

Oct 13, 1897

• 1st person to discover the electron
• Developed pudding model of the atom, which desrcibes the atom as a positive sphere w/ small electrons inside
• Developed a method for spreading different kinds of atoms & molecules

J. J. Thomson atom model

Oct 13, 1898

Marie & Pierre Curie

Oct 13, 1898

• Stated that radioactive materials cause atoms to break down spontaneously; which then releases radiation in the form of energy and polonium
• Discovered Radium and Polonium

Max Plack

Oct 13, 1900

Max Planck

Oct 13, 1900

• Made the Quantum theory of energy ; proposed that energy is radiated in very small amounts instead of an unbroken continuous wave
• Einstein used his theory to describe the particle properties of light

Robert Millikan

Oct 13, 1908

• Discovered the charge of an electron
• Specified the sir of the electron charge

Robert Millikan Oil drop experiment

Oct 13, 1908

Ernest Rutherford

Oct 13, 1911

• Eplained natural radioactivity
• Determined the structure of the atom
• Changed 1 element into another by splitting its nucleus
• Discovered concept of radioactive half life
• Protons in core of atom
• Electrons surrounded core

Ernest Rutherford atom model

Oct 13, 1911

Niels Bohr

Oct 13, 1913

• Suggested electrons travel around the nucleus in definite paths; when they jump from one path to another, a light quantum is released
• Created Bohr model

Bohr atom model

Oct 13, 1913

Henry Moseley

Oct 13, 1914

• Mentor was Rutherford
• Developed the application of x rays to study atomic structure
• Discoveries led to a more accurate placement of elements in the periodic table b/c of the closer determination of atomic #s

Henry Moseley atom model

Oct 13, 1914

Erwin shrodinger

Oct 13, 1926

• Quantum mechanical model of the atom (electron cloud)
• Used mathematical equations to describe the likelihood of finding an electro in a certain position
• Developed idea of sub energy levels

Erwin Shrodinger atom model

Oct 13, 1926

Werner Heisenberg

Oct 13, 1927

• Used quantum mechanics to interpret the behavior of elementary particles & atoms ( position and velocity )

Werner Heisenberg atom model

Oct 13, 1927

James Chadwick

Oct 13, 1932

• Discovered the neutron
• Inspired the US government to begin serious atomic bomb research efforts

James Chadwick atom model

Oct 13, 1932