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Democritus
Democritus hypothosized that all matter was made of atoms. The popular belief at the time was Aristotle's theory that all matter was made of four elements- fire, water, earth, and air. -
John Dalton
Dalton descibed atoms as "spherical solid masses in motion." He said that each element is composed of atoms, that all the atoms in one element are the same, that atoms of different elements are different, that atoms are rearanged, not changed, by chemical reactions, that compounds are formed when atoms of different elements combine, and that a compound is defined by the number, type, and proportion of the elements that make it up. His model of the atom was a sphere that is the same throughout. -
JJ Thomson
Thomson discovered the electron. He discribed atoms as a ball of positive chage containing electrons. He experimented with cathode ray tubes. Different gasses placed in the tubes generated streams of particles and conducted current. His model of the atom is often called the chocolate-chip cookie model. -
Ernest Rutherford
Rutherford used the "gold foil" experiment to determine that the nucleus of the atom is dense and had a positive charge, thus discovering the proton. He assumed that the electrons are outside the nucleus. He also discovered that the atom is mostly empty space. -
Neils Bohr
Bohr explained the structure of the atom as orbital shells of electrons. This model is known as the Bohr planetary model. He said the electrons moving around the atoms hace a set amount of energy. -
Schrodinger
Schrodinger identified the electron cloud as a probable location of moving electrons using a mathmatical description. -
Chadwick
Chadwick discovered a particle within the nucleus with a similar mass to the proton but with no charge, called the neutron. -
John Cockroft & Ernest Walton
Cockroft and Walton began to work on the acceleration of protons. They bombarded lithium with high energy protons and succeeded in transmuting it into helium. This was one of the earliest experiments to change the atomic nucleus of one element to a different nucleus by artificial means. This feat was popularly – if somewhat inaccurately – known as "splitting the atom." -
Atomic bomb
The first atomic bomb was created by using Uranium and splitting the atom. It was tested on this day.
