ATOMIC THEORY TIMELINE

DEMOCRITUS

• He was a Greek Philosopher
• First to suggest the existance of atoms
• Said that atoms are indivisible and indestructible
• He did not use the scientific method, so he did not have experimental support

JOHN DALTON

• He was an English chemist and teacher
• He expiremented with atoms and came up with three parts of his Atomic Theory:
• 1. Elements are composed of atoms
• 2. All atoms in an element are identical
• 3. Atoms combine in whole-number ratios that form compounds and molecules

JJ THOMSON

• He was an English physicist
• He discovered the electron
• He did this by using an electrode and bending the electricity using magnets
• This proved that atoms have a negative charge, thus explaining the electron
• His findings changed Dalton's first statement in his Atomic Theory

JJ THOMSON

• His findings stated that:
• 1. Atoms are breakable
• 2. The electrons are suspended in a positively charged field
• 3. The atom must have a great amount of empty space
• The new model of this atom is called the Plum Pudding Model

EUGNE GOLDSTINE

• He observed cathode rays
• His observations showed that atoms also have a positively charged particle
• He called these Protons

ERNST RUTHERFORD

• He was a former student of Thomson and worked at the University of Manchester
• He tested the theory of the Plum Pudding Model using his Gold-Foil Expirement
• His results did not prove the plum pudding model, but rather disproved it
• In his experiment resulted in:
• 98% of particles going stright through, 2% were deflected, and 0.01% bounced back

ERNST RUTHERFORD

• His results made him conclude that:
• An atom has a nucleus with a positive charge
• It also contains most of the weight
• This is called the atomic model

NIELS BOHR

• He was a student of Rutherford
• He changed the atomic model to include how an atom changes due to light and energy
• His Model is only accurate for Hydrogen, an element with only one electron, due to the mathematics

NIELS BOHR

• His theory is that electrons are in energy levels
• Once a quantum amount of energy is released, the electron moves up to a higher energy level
• He stated that the further from the nucleus an electron is, the more energy it has

ERWIN SCHRÖDINGER

• He was an Australian physicist
• He created the Quantum-Mechanical Model of the atom
• He created an equation that predicted the probability of an electron being in a certain orbital
• He explained that each orbital closest to the electron has the most probability of containing an electron
• He proceeded to explain how each orbital contains shells and each shell contains subshells that can hold a certin number of electrons

JAMES CHADWICK

• He was an English physicist
• He confirmed the existence of Neutrons