Democritus' modelDemocritus' mentor, Leucippus, originally came up with the atomic theory, but it was then adopted by Democritus. The atomic theory stated that “The universe is composed of two elements: the atoms and the void in which they exist and move.” According to Democritus atoms were miniscule quantities of matter. Democritus hypothesized that atoms cannot be destroyed, differ in size, shape and temperature, are always moving, and are invisible. He believed that there are an infinite number of atoms.
Dalton's ModelElements are made of extremely small particles called atoms.
Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
Atoms cannot be subdivided, created, or destroyed.
Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
In chemical reactions, atoms are combined, separated, or rearranged.
Thompson's ModelThomson's atomic model was proposed in 1904 and was called the plum pudding model. It was introduced right after Thomson's 1897 discovery of the electron, then called corpuscles. He said that no matter where matter came from, it contained particles that were the same and are smaller than the atoms that matter is formed from. The model was a round thick liquidy substance whose total charge canceled out the charge of the electrons.He came to this conclusion by using a cathode ray scope.
Rutherford's modelThese deflections were not consistent with Thomson's model. Rutherford was forced to discard the Plum Pudding model and reasoned that the only way the alpha particles could be deflected backwards was if most of the mass in an atom was concentrated in a nucleus. He thus developed the planetary model of the atom which put all the protons in the nucleus and the electrons orbited around the nucleus like planets around the sun.
Electron Cloud ModelThe electron cloud model is an atom model wherein electrons are no longer depicted as particles moving around the nucleus in a fixed orbit. Instead, as a quantum mechanically-influenced model, we shouldn’t know exactly where they are, and hence describe their probable location around the nucleus only as an arbitrary ‘cloud’.
Bohr ModelThe Bohr Model has an atom consisting of a small, positively-charged nucleus orbited by negatively-charged electrons. Here's a closer look at the Bohr Model, which is sometimes called the Rutherford-Bohr Model.