-
400
Democritus
Postulated the theory of atoms and void; the universe is made
up of empty space and a nearly infinite number or invisible
particles differing in arrangement, form, and position. He
stated that all all matter is composed of indivisible atoms. -
Isaac Newton
Isaac Newton theorized a mechanical universe with small, solid masses in motion. Newton also suggested that atoms were held together by attractions that we call forces. -
John Dalton
John Dalton proposed that elements consisted of atoms that were identical and had the same mass and that compounds were atoms from different elements combined together. He also proposed an atomic theory with spherical solid atoms based upon measurable properties of mass. -
George Johnstone Stoney
Stoney is most famous for introducing the term electron as the fundamental unit quantity of electricity. He proposed that electricity was made of discrete negative particles he called electrons. -
Joseph John Thomson
J.J. Thomson determined the charge to mass ratio of electrons. Developed the plum-pudding model of the atom. Describes the atom as a slightly positive sphere with small electrons inside. -
Ernest Rutherford
Ernest Rutherford publishes his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. Rutherford came to this conclusion following the results of his famous gold foil experiment. Rutherford also discovered alpha, beta, and gamma rays in radiation. -
Niels Bohr
Niels Bohr proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit. -
Louis de Broglie
Broglie proposed that electrons could behave as waves under some conditions, a finding that helped scientists understand that the atom didn't behave like the solar system because electrons do not move in regular orbits. -
Quantum Mechanical Model
Shows different orbits of electrons surrounding the nucleus in different energy levels. -
Erwin Schrodinger
Schrodinger used mathematical equations to describe the location and energy level of an electron. He developed the quantum mechanics model (the widely accepted atomic model today). -
Aristotle
Aristotle’s theory made a great generalization off all matter being made of the four elements: fire, water, earth, and air. He also believed that there were four qualities to these elements: dryness, hotness, coldness, and moistness.
