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460 BCE
Democritus (Democritus Model)
Democritus's model stated that matter consists of invisible particles called atoms and a void (empty space). He stated that atoms are indestructible and unchangeable. Also that they are homogenous, meaning they have no internal structure. How was the model wrong?
Democritus believed that the atoms differed in size and shape, were in constant motion in a void, collided with each other; and during these collisions, could rebound or stick together. -
400 BCE
Democritus (Democritus Model)
Democritus’s model stated that matter consists of invisible particles called atoms and a void (empty space). He stated that atoms are indestructible and unchangeable. Also that they are homogenous, meaning they have no internal structure. His atomic model was solid, and stated all atoms differ in size, shape, mass, position and arrangement, with a void exists between them. -
Dalton (Billiard Ball Model)
Dalton's atomic theory proposed that all matter was composed of atoms, indivisible and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass. -
Dalton (Billiard Ball Model)
The indivisibility of an atom was proved wrong: an atom can be further subdivided into protons, neutrons and electrons.According to Dalton, the atoms of same element are similar in all respects. -
Thompson (Plum-Puddin Model)
Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup." Rutherford's gold foil experiment showed that the atom is mostly empty space with a tiny, dense, positively-charged nucleus. -
Thompson (Plum-Puddin Model)
He argued that the plum pudding model was incorrect. The symmetrical distribution of charge would allow all the α particles to pass through with no deflection. Rutherford proposed that the atom is mostly empty space. The electrons revolve in circular orbits about a massive positive charge at the centre. -
Rutherford Model
Rutherford, described the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun. -
Rutherford Model
He couldn't tell why negatively charged electrons remain in orbit when they should instantly fall into the positively charged nucleus. Then in 1913, Neils Bohr solved it. -
Bohr (Planetary Model)
He described the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the center. -
Bohr (Planetary Model)
Discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element.
The problem is that it works very well for atoms with only one electron, but not at all for multi-electron atoms. -
Schrödinger (Cloud Model)
Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. -
Schrödinger (Cloud Model)
The disadvantage is that it is difficult to imagine a physical model of electrons as waves. The Schrödinger model assumes that the electron is a wave and tries to describe the regions in space, or orbitals, where electrons are most likely to be found
