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400 BCE
Democritus Atomic Model
The model stated that matter consists of invisible particles called atoms and also void. He knew that if cutting a stone in half each piece had the same properties. he contribute that help understand atom is that it is an indestructible and unchangeable. He's theory is relevant today because in his time he din't have enought instruments. all his theories are "mind experiments". -
Daltons Model Of Atom
Dalton's theory has 5 main points : everything is composed of atoms, all atoms of element are identical, the atoms of elements vary in size and mass, compounds are composed by combinated atoms and a chemical reaction results in the rearrangement of atom. His theory was revised to incorporate the existence of atomic isotopes .his importance has been recognized by designating the atomic mass unit as a Dalton. -
Thomson Atomic model: Plum pudding model
The model consists in the sea of uniform positive charge with the electron distributed in all the parts. He conducted experiment using a cathode ray tube. He observed that these rays could defect the magnetic fields. the main contribution is the electrons. the problem was demonstrated that the atom had a uniform positive charge, five years later in would come to known as the gold foil experiment. -
Rutherford atomic model: Gold foil experiment
His model shows that an atom is mostly empty spaces . for this he performs an experiment shooting a beam of alpha particles at a sheet of gold foil . He found that the atom consists mostly of empty space with its mass concentrated in a central positively charged nucleus. the problem with the model was that it could explain why negative charged electrons remain in orbit when they should fall into positive charged nucleus . -
Bohr atomic model: Planetary Model of the Hydrogen Atom
The model shows the atom as a small positive charge nucleus surrounded by orbiting electrons. the main problem with the Bohr's model is that it works very well for atoms with only one electron; it breaks down when applied to multi-electron atoms. The main contribution was the discover that electrons travel separate orbits around the nucleus and the number of electrons determine the properties of an element. -
Schrödinger atomic model: Quantum Mechanics Model
He accounted for the electrons wave and particle properties. provides equation relating the distance an electron could be found. main contribution where the energy level are divided into sublevels and this into orbits, and we can't know for sure an electron atual location. the disadvantage of this model it that it is difficult to imagine a physical model of electron as waves.
