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400 BCE
Democritus
He believed that you could only split matter in half a certain amount of times and eventually you would get to what he called an atom. This he claimed was the smallest thing in the world and could not be split in half. -
John Dalton
He was the first to recognized the existence of atoms and elements and gave atomic weigh to some of them. He also proposed atomic theory in 1803 -
Solid Sphere Model
Created by John Dalton, Illustrated an atom as a solid sphere of mass. -
Henri Becquerel
He discovered radioactivity that allowed later scientist to perfect the atomic model and worked with magnetism of atoms. -
JJ Thomson
He discovered the existence of the electron and created the plum pudding model where the atom was positive and had negative charges wondering around. -
Max Planck
He developed quantum theory and stated that energy is given off in little packets -
Plum Model
Created by JJ Thomson, it suggested atoms were made up of positive and negative charges and that the negative electrons were a lot smaller than positive protons, like plum pudding. -
Albert Einstein
He discovered the theory of relativity and that light was made of different particles. -
Hans Geiger
He developed an electrical device the clicked when it hit alpha particles named the Geiger counter. -
Robert Millikan
He did the oil drop experiment discovering a way to determine the mass and unit of charge of the electron. -
Ernest Rutherford
Created a nuclear model after his gold foil experiment his model had a positive charged middle and negatively charged electrons around the protons as well as a lot of empty space. -
Rutherfords Model
Created by Rutherford, it shows that the atom is mostly made up of empty space. -
Henry Mosely
Used X-rays to find frequency of elements and determined the number of protons correlates with the atomic number. -
Niels Bohr
Decided to make a new model, he created energy levels in atoms and only a certain amount of electrons could be on each level. -
Planetary or solar system Model
Created by Neils Bohr, it illustrated the negatively charged electrons orbiting the positively charged nucleus like the planets. -
Electron Cloud Model
Created by Erwin Schrotinger, His model illustrated the electrons orbiting the nucleus in a cloud. -
Erwin Schrodinger
He built off of Bohr's atomic model and believed it was unlikely that an electron would stay in one position. -
James Chadwick
Chadwick discovered the existence of the neutron. -
Bibliography
“Atomic Structure Timeline.” Homepage, atomictimeline.net/. Brown, Theodore L., and Michael W. Lufaso. Chemistry: the Central Science. Pearson, 2019. Johnson, Rebecca L. Atomic Structure. Twenty-First Century Books, 2008. Models Of The Atom. www.siyavula.com/read/science/grade-10/the-atom/04-the-atom-02.
