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450 BCE
Democritus discovers the atom
He took a seashell and broke it in half then took that half and broke it in half over and over and over and over again until he was finally left with a fine powder, he then took the smallest piece from the powder and tried to break that but could not. He created the atomic theory which is something can only be broken down so far and what you have left is an atom -
Dalton brings back the atom
Experiments he did was;studied the pressure of gases,concluded that gases must consist of tiny particles in constant motion,researched properties of compounds,showed a compound always consists of the same elements in the same ratio,different compounds always consist of different elements or ratios.can happen only if elements are made of tiny particles that can combine in a variety of ways.Created the atomic theory which states that atoms are the smallest things and cannot be broken down anymore -
Thomson Adds Electrons
He did a vacuum tube experiment:when connected to a power source one end is negative and the other positive,the electric current flowed through the tube from the negative to positive end.Showed that electric current is negative in charge,observed that the positive and negative plates along the sides caused the electric current to bend toward the positive side showed that the charge is carried by particles of matter.Said that an atom is like a plum pudding,which has plums scattered through it -
Rutherford Finds the Nucleus
The Gold Foil Experiment proved the existance of a small massive center to atoms, which would later be known as the nucleus of an atom. Discovered that some elements give off positively charged particles,named them alpha particles,in 1911 he used them to study atoms.He aimed a beam of alpha particles at a very thin sheet of gold foil.Outside the foil,he placed a screen of material that glowed when alpha particles struck it. -
Bohr creates the Bohr model
Proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted. Bohr's theory could explain why atoms emitted light in fixed wavelengths.
