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450 BCE
Democritus
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, as well as homogenous. -
Dalton
His theory stated that the atoms are indivisible, and that atoms are identical. One of its main contributions was that Dalton based his theory on the law of conversation mass and the law of constant composition. His model was incorrect because the indivisibility of an atom was proved wrong: an atom can be further subdivided into protons, neutrons and electrons. -
Thomson
In this model, the atom is composed of electrons
surrounded by a soup of positive charge electrons,
One of the main contributions of this model was that Thomson's experiments with cathode ray tubes showed that
all atoms contain tiny negatively charged subatomic particles
or electrons. This model failed to explain how the positive charge holds on the electrons inside the atom. It also failed to explain an atom's stability. The theory did not mention anything about the nucleus of an atom. -
Rutherford
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. This model, however, used classical physics and not quantum mechanics. meaning that an electron circling the nucleus would give off electromagnetic radiation. The electron would lose energy and fall into the nucleus. -
Bohr
The Bohr Model is a planetary model in which the negatively charged electrons orbit a small, positively charged nucleus similar to the planets orbiting the sun. In 1913, Bohr's theory could explain why atoms emitted light in fixed wavelengths. Some of the reasons why it was wrong are that It violates the Heisenberg Uncertainty Principle because it considers electrons to have both a known radius and orbit, and it provides an incorrect value for the ground state orbital angular momentum. -
Schrödinger
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. An example of its contributions is electrons have an intrinsic property called spin, and an electron can have one of two possible spin values: spin-up or spin-down. Any two electrons occupying the same orbital must have opposite spins. To this day, it has not been proven to be wrong.