-
450 BCE
The idea of atoms are discovered.
Democritus, a Greek philosopher, took an apple and cut it as small as he could. He kept cutting and cutting until he reached the point where he determined that his pieces could not get any smaller. He called these "atomos". Aristotle, a much more famous philosopher, denied Democritus's theorem and the idea of "atomos" was dismissed for 2000 years. -
The atom bounces back.
John Dalton, a british chemist, noted observations in gases which led him to believe atoms were true. His atomic theory states three things: All substances are made of atoms, all same atoms have same masses, and atoms join together to form compounds. His theory was widely accepted. He displayed his research through hooks and wooden balls. -
Knowledge increases through research.
JJ Thompson had heavy influence on the idea of atoms through his own research. His experiments consisted of vaccum tube experiments which led him to believe that there was electricity in the atoms. Therefore, Thompson found what are called "electrons" and denounced the theory that atoms were pure matter. His "plum pudding model" displayed an atom that resembles plum pudding, electrons in a pool of positivity. -
The nucleus was found.
Ernest Rutherford was influential in the idea of the atom because he was the one who discovered the nucleus. He expected in his "Gold Foil Experiment" that alpha particles would be reflected off of gold foil due to both their positive charge, backed by Thomson's theories. However, he discovered that the alpha particles actually went straight through the foil. This led him to believe that the positively charged nucleus was very small and packed together. -
Line emissions and alpha particles change the game.
Danish scientist Niels Bohr discovered electrons revolve (orbit) around the nucleus. He found that if an electron were to jump from one orbit to another, a light would be emitted, otherwise known as the Line Emission Spectrum. He conducted an experiment where electricity running through a glass tube caused electrons to gain energy. This causes a different light to be emitted for each and every element. -
But do they orbit?
Erwin Schrodinger discovered that electrons don't necessarily orbit, and that it's not very important to know where they are. It's not possible to calculate the exact position of an electron but it is estimable based on energy levels which determine its distance from the nucleus. -
Welcome to neutrons.
James Chadwick discovered neutrons which accounted for the heavy mass and low proton count in the atom. He theorized that neutrons were just neutral particles that contributed to an atom's atomic mass and concluded that neutrons, along with protons, are part of the nucleus. His experiments with alpha particles being shot at beryllium produced an unexpected radiation. This was when he discovered a neutral electricity. -
Sources
Information:
-Chem Packets A1, A2, A3
-CK-12 History of the Atom Photographs:
-United States Library of Congress's Prints and Photographs
