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307
Democritus
307 BC: stated that all matter is made up of atoms. He also stated that atoms are eternal and invisible and so small that they can’t be divided, and they entirely fill up the space they’re in. -
400
Aristotle
400 BC: He didn't think atoms could be in constant motion in a void. Aristotle also said there were only four elements (earth, air, fire, water) and that these had some smallest unit that made up all matter. -
Antoine Lavoisier
Did not himself think of matter in terms of atoms, but whose work laid organization groundwork for thinking about elements. He distinguished between an element and a compound. -
John Dalton
All matter is made of atoms. Atoms are indivisible and indestructible. Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. -
Max Planck
Planck's work in thermodynamics led to the formulations of his quantum theory. To explain the colors of hot glowing matter, he proposed that energy is radiated in very minute and discrete quantized amounts or packets, rather than in a continuous unbroken wave. -
James Maxwell
Proposed electric and magnetic fields filled the void. -
Marie Curie
She created of a theory of radioactivity and also the discovery of two new elements, radium and polonium. -
JJ Thomson
His atomic theory identified that atoms were not invisible.
Thomson suggested that the model of an atom as a sphere of positively charged matter with negatively charged electrons surrounding them. He stated that electrons were positioned by electrostatic forces. -
Robert Millikan
Discovered the calculation of the mass of the electron and the positively charged atoms. -
Ernest Rutherford
He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus. -
Henery Moseley
Using x-ray tubes, determined the charges on the nuclei of most atoms.This work was used to reorganize the periodic table based upon atomic number instead of atomic mass. -
Niels Bohr
Discovered that electrons orbit around the nucleus. -
Werner Heisenberg
Described atoms by means of formula connected to the frequencies of spectral lines. Proposed Principle of Indeterminancy - you can not know both the position and velocity of a particle. -
Erwin Schrodinger
Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom. -
James Chadwick
Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron. -
Modern Electron Cloud Model
The electron cloud model shows electrons moving in a cloud around the nucleus. In this covalent bond, two H atoms "share" their single electrons, to form a pair of shared electrons.
