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300
Aristotle
Aristotle is credited for discovering the four "elements", which he named air, fire, water, and earth. He believed in reasoning in substitution of scientific experiments. -
400
Democritus Atomic model
- Democritus of Adbera is credited for the term atomos, meaning indivisible. He was the first to identify the possibility of an atom and deem it as the smallest piece of matter.
- To Democritus, atoms were small, hard particles that were all made of the same material but were different shapes and sizes. Atoms were infinite in number, always moving and capable of joining together.
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Antoine Lavoisier
- Antoine Lavoisier formulated the theory of conservation of mass. This showed that atoms couldn’t be created or destroyed, which supported the theory of Democritus.
- Lavoisier also showed that compounds are simply combinations of different types of atoms, further supporting the idea that atoms are indivisible.
- Provided crucial information for John Dalton’s model.
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Dalton Atomic Theory
- Pictured atoms as tiny, indestructible particles, with no internal structure.
- All matter is composed of atoms Atoms cannot be made or destroyed All atoms of the same element are identical Different elements have different types of atoms Chemical reactions occur when atoms are rearranged Compounds are formed from atoms of the constituent elements.
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Henri Becquerel
- Henri Becquerel discovered radioactivity in his research of uranium and other materials. This helped to show what happened when atoms were affected and observed.
- Becquerel shared a Nobel Prize with the Curies.
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J.J. Thomson Model
- Joseph John Thomson is credited with describing the nature of cathode rays. He also created the plum pudding model of the atom and discovered the electron.
- pictures electorns embedded in a sphere of positive electrical charges.
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Max Planck
- discovered an equation E=Nhf, with E=energy, N=integer, h=constant, f=frequency. In determining this equation, Planck came up with the constant (h), which is now known as "Planck's constant."
- Planck's discovery was that energy, which appears to be emitted in wavelengths, is actually discharged in small packets (quanta). This new theory of energy revolutionized physics and opened the way for Albert Einstein's theory of relativity.
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Hantaro Nagaoka
- In 1904, Hantaro Nagaoka developed an early but incorrect planetary model of the atom. He based his model of the atom around the rings of the planet saturn. however his model was not created properly. He explained that the rings are held there due to its massive orbit. although this model was wrong it still allowed for the discovery of the atoms rings.
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Robert Millikan
- He performed the oil drop experiment, which he completed with JJ Thomson.
- The oil drop experiment was meant to measure the charge of electrons. It involved balancing gravitational force with the upward buoyant forces on oil suspended between two metal electrodes. Through this experiment, Millkian and his partner deemed the approximate value of the electron as 1.5924(17)x10^-19C, which is within 1% of the present-day accepted value.
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Ernest Rutherford
- Ernest Rutherford is credited with the gold foil experiment. He stated that atoms have a small positively charged nucleus, and the remainder is empty space. He also predicted the existence of neutrons.
- discovered that atoms have a small,dense, positively charged nucleus, electrons move around the nucleus.
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Niels Bohr
electrons: proposed that electrons:
- orbit the nucleus without losing energy;
- could move only in fixed orbits of specific energies.
- Electrons with low energy would orbit closer to the nucleus while electrons with high energy orbit further from the nucleus. -
Louis deBrogile
- proposed that moving particles like electrons have some properties of waves and particles.
- introduced his theory of electron waves. This included the wave-particle duality theory of matter, based on the work of Max Planck and Albert Einstein on light. The thesis examiners, unsure of the material, passed his thesis to Einstein for evaluation
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Erwin Schrodinger
- developed mathematical equations to describe the motion of electrons in atoms. his work leads to the electron cloud method.
- after de Broglie had put forward his ideas, Schrodinger used them to write a wave equation to describe this new mechanics of particles. Schrodinger's model of the atom is not a physical model (where an object has size, shape and boundaries) but is a mathematical model. this is useful to predict some properties of objects (or atoms), but is not able to describe the atom.
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Werner Heisenburg quantum mechanics
- Werner Heisenburg is credited with the "uncertainty principle", which states it is impossible to determine the position and momentum of a particle at the same time. He is also credited with the "cloud" model, also known as the quantum mechanical model.
- The uncertainty principle states that there is a fundamental limit on the accuracy with which certain properties of a particle, how fast it's going or where it is, can't be exactly determined. It was a key discovery in early quantum theory.
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James Chadwick
- Chadwick smashed alpha particles into beryllium, a rare metallic element, and allowed the radiation that was released to hit another target: paraffin wax. When the beryllium radiation hit hydrogen atoms in the wax, the atoms were sent into a detecting chamber. In physics it is known that a particle having almost the same mass as a hydrogen atom could effect hydrogen in that matter.The experiment results showed a collision with beryllium atoms would release massive neutral particles,(neutrons).
