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450
Aristotle (around 460 B.C.)
Aristotle believed that all matter came from only four elements - earth, wind, fire, and water. He paid no mind to Democritus's theory, and provided the method of gathering scientific facts, which proved as the basis for all scientific work. He also thought that the validity of an argument was based on its structure: thesis. Aristotle wouldn't have known what the atom looked like because he didn't believe in Democritus's theory of atoms. -
450
Democritus (around 460 B.C.)
Democritus came up with the theory that matter could not possibly be divided forever and ever, that after a certain point matter became indivisible. The method he used to discover this was simple- all he had to do was ask himself: how many times can matter be cut into before it is too small to be divided any more? Democritus also came up with the theory that all atoms are such small, external particles, that you cannot see them. He thought they took up the space that contained them, entirely. -
John Dalton
John Dalton formed the atomic theory, which states that all matter is comprised of tiny, indestructible particles called atoms, which are all alike and have the same atomic weight. "Absortion of Gases" , an essay written by Dalton, is one of the earliest indications of his ideas about the Atomic Theory. he came up with the idea that all atoms are identical, and retain their indentity in chemical reactions. Another discovery made by this scientist is the formation of compounds by atoms. -
JJ Thomson
JJ Thomson was responsible for the discovery of electrons. His theory suggested that the atom is not indivisible, because it is made of smaller things, which he named protons and electrons. The Plum Pudding model is a famous model conducted by Thomson, displaying the idea that an atom consists of a sphere of positive charges with negatively charged electrons embedded in it.He also concluded that the positive and negative charges in an atom are equal in magnitude,so atoms are electrically neutral -
Ernest Rutherford
Rutherford stated that all the mass of an atom is in a positively -charged ball at the center of the atom, His invention of the Gold Foil Experiment is what aided his discovery that the atom has all of its mass concentrated in its center, a nucleus, with the majority of the atom consisting of empty space. While the nucleus contains virtualy all of the mass of the atom,it only takes up one-billionth of the volume of the atom, a very tiny amount. Electrons orbit the nucleus according to Rutherford -
Neils Bohr
Bohr proposed that electrons orbit the nucleus without losing energy, could only move in fixed orbits of specific energy, and that electrons with low energy would orbit closer to the nucleus while electrons with high energy orbit farther form the nucleus. Bohr came up with his model as a refined version of Rutherford's model. The Bohr Atomic Model suggests that atoms absorb or emit radiation only when the electrons abruptly jump between stationary states. -
Werner Eisenburg and Erwin Schrodinger
Heisenburg thought taht in order to view an electron in its orbit, you must shine a wavelength of light that is smaller than the electron's wavelength (this has a high energy). The electron would then absorb the energy which would change the electron's position. Schrodinger invented a derived set of equations, called "Schrodinger's Equation", the wave equation of non-realistic quantum mechanics. This showed that waves can be used to describe electrons in atoms.