Mid 300's BC (After Democritus)
* He did not believe in scientific experiments, but instead believed in reasoning
* He dismissed Democritus' atom idea as "worthless"
23rd Oct, 0300
Aristotle ~ 300 BC
Mid 300's BC (After Democritus)
* He had the opinion that four basic qualities determine the constitution of a substance
* the four "elements": earth, fire, air, and water
21st Oct, 0400
Democritus of Adbera ~400 BC
* was the first to identify the possibility of an atom and that the atom was the smallest piece of matter
* the atom was named after the Greek word atomos, which means indivisible
* Known as the Father of the Modern Atomic Theory
* Had 5 parts to his theory
1.All matter is composed of called atoms.
2.All atoms of a given element are identical.
3.Atoms cannot be created, destroyed, or subdivided.
4.In chemical reactions, atoms combine with or separate from other atoms.
5.In chemical reactions, atoms combine with each other in simple, whole-number ratios to form combined atoms
* Part of his theory includes that elements are composed of atoms and that the atoms of elements are identical in mass
Joseph John (J.J.) Thomson
discovers the electron
described the nature of cathode rays
plum pudding model of the atom
* measured the charge of an electron
* performed the oil drop experiment
* completed with Thompson
Rutherford discovered alpha, beta, and gamma rays in radiation.
Max Planck proposed the idea of quantization to explain how a hot, glowing object emitted light.
determined atoms can emit "quants"
Einstein used his work to study photons
Conducted the gold foil experiment:
Rutherford fired tiny alpha particles at solid objects such as gold foil. He found that while most of the alpha particles passed right through the gold foil, a small number of alpha particles passed through at an angle (as if they had bumped up against something) and some bounced straight back like a tennis ball hitting a wall. Rutherford's experiments suggested that gold foil, and matter in general, had holes in it!
discovers electrons travel in specified energy levels; and spectrum lines are produced when electrons move.
He comes up with his planetary model of the atom
Determined the atom has a small nucleus, and the remainder is empty space
predicted the existence of neutrons
Niels Bohr proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit.
Louis de Broglie
added to Bohr's model of the atom by reasoning that, since light could act like a particle, an electron could act like a wave.
Determined that electrons have properties of both waves and particles
this group of waves is named after this scientist
* showed that waves can be used to describe electrons in atoms by using mathematics
* He determined the probability location of electrons in atoms
* creator of the "Uncertainty Principle" which says the more precisely the position is determined, the less precisely the momentum is known
* found it impossible to determine the position and the momentum of a particle at the same time
* had the "cloud" model aka the quantum mechanical model
*Quantum mechanics describes the time evolution of physical systems via the wave function
*The wave function encapsulates the probability that the system is to be found in a given state at a given time
discovered neutrons, particles whose mass was close to that of a proton.
helped with the development of the nuclear model