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Period: 400 to
Timespan
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442
Aristotle and Democritus
First early scientist from 350BC and 442BC. Aristotle believed in the existance of tiny geometric atoms but Democritus created a basic atomic theory. This theory was all logically based because experiments were not necessary. The theory said that all matter was seperated into indivisible particles, atoms (atomos). -
Antoine Lavoisier
Lavoisier was an early scientist who discovered the law of conservation of mass. This law states that mass cannot be created or destroyed. In other words, this means that in the beginning of a chemical reaction the mass combined will equal the mass after the reaction. -
John Dalton
Dalton was a British scientist best known for his modern atomic theory and his creation of the spherical model. His atomic theory stated that 1) all elements are composed of small indivisible particles called atoms. 2) Atoms of the same element are identical and those of different element are different. 3) Atoms of different elements can mix together to form compounds. 4) Chemical reactions occur when atoms are separated, joined, or rearranged. -
John Dalton (Continued)
The Spherical Model created by Dalton was simply a small dense sphere which could not be broken into smaller parts. This was a very simple and easy model of the atom which was formulated early. -
Joseph Proust
Proust had a great contribution to the Law of Definite Proportions. This law stated that a chemical compound always contains the exact same amount of elements by mass. This law was stated in 1806. -
J.J. Thomson
Thomson is most known for his discovery of electrons and his "plum pudding" model. His discovery of the electron was due to his experiments with the cathode ray tube. Thomson sent electricity through a cathode ray tube and observed the gases at low pressure glowing. This led him to discover the negatively, small, massless, electron. -
J.J. Thomson (continued)
Thomson's model of the atom represented a plum pudding because of the positive "pudding" base and the negative "plums" on top. This was a simple design of the atom and also an early representation. -
Max Planck
Planck was a German scientist who is known to be the founder of the Quantum Theory. The Quantum Theory explains the nature of matter and energy at a in atomic and subatomic particles. The theory now states that energy occurs in units and not in waves as previously thought. -
Robert Millikan
American scientist who made many discoveries in the field of electricity. he determined the charge of the electron by completing the "falling-drop method". He also proved that quantity of electrons was constant in 1910. -
Ernest Rutherford
Rutherford's contributions to society included his discovery of the nucleus by the gold foil experiment, and his nuclear model of the atom. Rutherford completed an experiment where he shot alpha particles at gold foil. Most particles passed right through, but a few bounced back, proving the existence of small nuclei. -
Ernest Rutherford (continued)
Rutherford created the nuclear model of the atom. This model included a small dense nucleus with electrons orbiting around it. Most of this model is empty space, showing why most alpha particles passed right through. -
Niels Bohr
Danish scientist who contributed by his creation of the Bohr model of the atom. The Bohr model is a small dense nucleus with electrons orbiting just like the nuclear model, but the electrons are specifically distanced. There is an amount of fixed energy to distance the electrons. Bohr brought up the idea of orbits around the nucleus, much like planets. -
Louis De Broglie
De Broglie's contribution as a scientist was the proposal that moving particles such as electron have properties like waves. With a few years, De Broglie's proposals were proven correct and are used today. De Broglie is also credited for the founding of the proton, subatomic particle. -
Werner Heisenberg
Heisenberg is accurately associated with the uncertainty principle because he was the main founder of it. The uncertainty principle states that you can never know the exact position of an atom or any parts of the atom just like you would with larger objects with velocity. -
Quantum Mechanical Model
The Quantum Mechanical Model was introduced and credited by Erwin Schrodinger. This is the most modern model of the atom. The model shows a small dense nucleus, surrounded by multiple scattered electrons in a "cloud". This model is also called the electron cloud model.
