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450 BCE
Empedocles
Theory of 4 classical elements, Fire, Water, Earth, Air. -
Period: 450 BCE to
4 Elements Theory
Theory of 4 classical elements, Earth, Fire, Water and Air -
400 BCE
Leucippus & Democritus
Atom (uncuttable). This two philosophers thought that atoms were infinite, uncreated and eternal, also that the qualities of an object were based on the qualities of the atoms that compose it. -
350 BCE
Aristotle
He supports the idea of the 4 elements of Empedocles, This idea thanks to Aristotle's importance will last for almost 2000 years. -
Antoine Laurent de Lavoisier
"Matter is neither created nor destroyed, it just changes form" -
John Dalton
His model was result of a series of experiments he realized with gases, and based on the law of mass conservation.
All the matter is made of atoms.
The atoms are indivisible and indestructible.
All the atoms of an specific element are all identical.
The atoms of different element have different mass and properties.
The compounds are formed by a combination of two or more kinds of different atoms.
A chemical reaction is a reorganization of atoms.
He also guessed the atomic mass of some elements. -
Period: to
John Dalton's Atomic Model
First atomic model with scientific bases. -
Amedeo Avogadro
He made the first difference between atoms and molecules.
He discovered that a gas in specific temperature, pressure and volume, always has the same number of particles. It doesn't matter if they are atoms or molecules. -
Dmitri Ivanovich Mendeleev
He was the precursor of the Periodic Table, when he decided to organize the chemical elements in increasing order of their atomic mass. -
Joseph John Thomson (Cathode Ray Tube Experiment) (Electron)
Discover of the Electron.
Thomson discovered the electron while doing an experiment with the cathode ray tube. He put the tube between two plaques with opposite charges, the ray was moving away of the negative one and going closer to the positive, from this fact he discovered that the ray had a negative charge.
He did the following statements:
The cathodic ray is formed of negative particles
The particles are part of the atom, because their mass is 1/2000 of the atom's mass
They are in each atom -
Joseph John Thomson
The Plum Pudding Model
In this model the atom is formed by electrons of negative charge set in a positive atom, as if they were plums in a pudding.
In this model the number of negative charges was the appropriate for neutralize the positive charge. If the atom loses an electron, the structure will be positive, in the other hand if it wins an electron, it will be negative. In this way he explained the formation of iones, but he didn't explain the other kinds of radiations. -
Period: to
Joseph John Thomson's Atomic Model
The Plum Pudding Model -
Ernest Rutherford (Metal/Gold Foil Experiment) (Proton) + Hans Geiger & Ernest Marsden
In this experiment they discovered that each atom has a nucleus where all the positive particles and the majority of its mass is found.
They measured how an alpha particle beam (+) is scattered when it strikes a thin metal foil.
With it they proved that Thomson's model was wrong, based on his model, all the alpha particles should have passed through the foil with minimal scattering, but most of the particles went straight through the foil, some were slightly moved and a few were rejected back. -
Ernest Rutherford
This new atomic model is based on Rutherford's experiments and is the first one telling that the atoms have a nucleus, in this nucleus is where he said that all the positive charge and almost all they mass was found. He proposed that the electrons where in an orbit around the empty space surrounding the nucleus.
His estimations suggested that half of the nucleus was empty, this is the reason why in 1920 he predicted the existence of neutrons. -
Period: to
Ernest Rutherford's Atomic Model
Electrons in orbits around the nucleus formed by protons. -
Niels Bohr
This atomic model tries to solve Rutherford's model problems
Bohr starts with Rutherford's atomic model and tries to incorporate the absorption phenomena and the gas emission, also the new quantum theory by Max Planck and the phenomenon of the photoelectric effect by Albert Einstein.
Each orbit has a different energy, more energy as far far from the nucleus
Electron don't emit light while being in a stable orbit.
Electrons can jump from one orbit to other absorbing (-+) or emitting (+-) energy. -
Period: to
Niels Bohr's Atomic Model
Electrons in orbits around the nucleus formed by protons, the electrons can jump from one orbit to other. -
Erwin Schrödinger
Schrödinger changes the way of represent atoms, the electrons instead of being in orbits around the nucleus are now in orbitals, which means that they are represented in the most likely zone where they are going to be find. -
Period: to
Erwin Schrödinger's Atomic Model + Modifications
Electrons are found in orbitals instead of orbits. Nucleus formed by protons and neutrons. -
Werner Heisenberg
He is known for his uncertainly principle, this principle says that is imposible to measure the position and the linear movement of a particle at the same time. -
James Chadwick (Beryllium Foil Experiment) (Neutron)
Chadwick bombarded beryllium with alpha particles (+), he observed an emission of high radiation coming from the metal, this radiation was similar to gamma radiation. After the experiment he arrived to the conclusion that this radiation was formed by neutral particles with a mass slightly bigger then protons.
