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442 BCE
Democritus
Democritus’s model stated that matter consists of invisible particles called atoms and a void (empty space). His atomic model was solid, and stated all atoms differ in size, shape, mass, position and arrangement, with a void exists between them.
Democritus called these infinitesimally small pieces of matter atomos, meaning "indivisible" and he used the term for the first time.. Even though he was right, some of its postulates were not; now we know the existence of subatomic particles . -
400 BCE
ATOMIC MODELS
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John Dalton "BILLIARD BALL MODEL"
Based on all his observations, Dalton proposed his model of an atom. It is often referred to as the billiard ball model. He defined an atom to be a ball-like structure, solid and indestructible . If you asked Dalton to draw the diagram of an atom, he would've simply drawn a circle. Even thought his ideas were advanced, he didn´t count on the existence of electrons, protons and neutrons. -
Dalton´s model representation
He also used the cathode ray experiment -
J. Thomson "PLUM PUDDING MODEL"
He discovered electrons and stated that atoms are positive solid spheres with negartive electrons on their surface, so it was made most of empty space. It resembles a plum pudding because the electrons in the model look like the dry fruits embedded in a sphere of positive charge just like a spherical plum pudding. He used the cathode ray experiment. Thomson's error was the visualization of the atom, since this was not exactly a mass -
Thomson´s model representation
PLUM PUDDING MODEL
He discovered the electrons, also said that atoms are positive solid spheres with electrons on their surface. Thomson used the Cathode ray experiment: build a cathode ray tube with a metal cylinder on the end. This cylinder had two slits in it, leading to electrometers, which could measure small electric charges. -
Rutherford "NUCLEAR ATOM"
The model 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. He discovered protons and stated that atoms are mostly empty space. -
Rutherford´s model representation
NUCLEAR ATOM
He discovered protons, also said that atoms have a small positive
nucleus with electrons moving around and that atoms are mostly empty space. Rutherford established the nuclear theory of the atom with his gold-foil experiment. When he shot a beam of alpha particles at a sheet of gold foil, a few of the particles were deflected. He concluded that a tiny, dense nucleus was causing the deflections. -
Bohr "SOLAR SYSTEM MODEL"
The Bohr model and all of its successors describe the properties of atomic electrons in terms of a set of allowed (possible) values. Atoms absorb or emit radiation only when the electrons abruptly jump between allowed, or stationary, states. He stated that electrons moved around the nucleus in circular orbits energy levels. -
Bohr´s model representation
SOLAR SYSTEM
In this Bohr explained that electrons move around the nucleus in circular orbits, he also discovered the energy levels -
Schrödinger "QUANTUM MECHANICS/ELECTRON CLOUD"
The quantum mechanical model does not define the exact path of an electron, but rather, predicts the odds of the location of the electron. This model can be portrayed as a nucleus surrounded by an electron cloud. Where the cloud is most dense, the probability of finding the electron is greatest, and conversely, the electron is less likely to be in a less dense area of the cloud. Thus, this model introduced the concept of sub-energy levels. -
Schrödinger "ATOMIC MODEL"
-The schrodinger model does not take into account the quantum number of the spin
-It does not explain why an electron in a quantum state decays to a lower state if there is some free
-Explain only the electronic structure of the atom and its interaction with the structure of other atoms
-Unaware of the relativistic effects that fast electrons have, this error is also repaired in the equation created by Dirac, in which it includes a description of the electronic spin. -
Schrödinger´s model representation
QUANTUM MECHANICS / ELECTRON CLOUD
He divided the energy levels in sublevels and the sublevels in orbitals, he also said that we cannot know the exactly location of an electron just an approximately.
