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600 BCE
Thales Of Miletus
Discovered that a piece of amber, after rubbing it with fur, attracts bits of hair feathers and other light objects. -
460 BCE
Greek Philosopher, Democritus
Developed the idea of atoms. He asked this question: If you break a peice of matter in half, and then break in half again, how many breaks will you have to make before you can break it further? DEmocritus thought that it ended at some point, a smalleest possible bit of matter. He alled thse basic matter particles, atoms. -
An English Chemist, John Dalton
Performed experiments with various chemicals that showed that matter, indeed, seem to consist of elementary lumpy particles (atoms). -
The English Physicist J.J Thompson
Discovered the electron and proposed a model for the structure of the atom. https://cdn.britannica.com/72/22472-050-5A467F43.jpg -
Max Planck a Professor of Theoretical Physics in Berlin
Showed that when you vibrate atoms strong enough, such as when you heat an object until it glows, you can measure the energy only in discrete unites. He called these energy packets, "quanta". https://theatomictheoryproject1.weebly.com/uploads/9/9/0/5/9905782/6514949_orig.gif -
Albert Einstein
Wrote a ground-breaking paper that explained that light absorption can release electrons from atom, a phenomenon called the photoelectric effect. https://assets.sutori.com/user-uploads/image/e756ccaa-007d-4841-83f5-ab45c69ff09d/fc3559cbc8a0988795e6419823a2c375.jpeg -
A New England Physicist Ernest Rutherford
Thought it would prove interesting to bombard atoms with these alpha rays, figuring that this experiment could investigate the inside of the atom (sort of like a probe). He used Radium as the source of the alpha particles and shinned them onto the atoms on gold foil. Behind the foil sat a fluorescent screen for which he could observe the alpha particles impact. https://d2jmvrsizmvf4x.cloudfront.net/ZRKfN5N6QwqHxGm6oH5l_RutherfordGoilFoil.jpg -
A Danish Physicist Niels Bohr
Came up with a theory that said the electrons do not spiral into the nucleus and came up with some rules for what does happen. Rule
1. Electrons can orbit only at certain allowed distances from the nucleus.
2. Atoms radiate energy when an electron jumps from a higher-energy orbit to a lower-energy orbit. Also, an atom absorbs energy when electron gets boosted from a low-energy orbit to a high-energy orbit. -
Rutherford's Atom
Wasn't until that Rutherford knew that atoms consist of a compact positively charged nucleus , around which circulate negative electrons at a relatively large distance. Rutherford finally identify the particles of the nucleus as discrete positive charges of matter. -
Bohr's & Sommerfeld
Further experiments showed that Bohr's model of the atoms had some troubles. Bohr's atom seemed too simple to describe the heavier elements. The special lines did not appear correct when a strong magnetic field influenced the atoms. Bohr & German Physicist Arnold Sommerfield expanded the original Bohr model to explain these variations. Bohr-Sommerfield model, not only do electrons travel in certain orbits but have different shapes and the orbits could tilt in the presence of a magnetic field. -
An Austrian Physicist Wolfgang Pauli
predicted that an electron should spin (kind of like a top) while it orbits around the nucleus. https://www.thoughtco.com/thmb/kbjhrxOMEikDFDewPl_HlTs4Oec=/768x0/filters:no_upscale():max_bytes(150000):strip_icc()/475158087-56a12f553df78cf772683a63.jpg -
English Physicist James Chadwick
Finally discovered the neutrons. He fund it to measure slightly heavier than the proton with ta mass of 1840 electrons and with no charge (neutral)
http://chadwicksphysics.weebly.com/uploads/1/7/3/4/17347989/5970964_orig.jpg -
Ancient Greek Until Today
The visual concepts of the atom has proved elusive and obscure, yet the mathematical concepts have grown stronger. ALthough nothing has yet proven absolute, humans can now predict the behavior of atoms with great accuracy.
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