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400
Democritus of Abdera: Atomic Theory of the Universe.
Essential points of his theory:
- Atoms are eternal, indivisible, homogeneous, incompressible, and invisible.
- Atoms differ only in shape and size, but not in internal qualities.
- The properties of matter vary according to the grouping of atoms.
Democritus started with a stone, which explained that if you cut it in half, you would get two pieces of the same stone and if you repeated the operation continuously, you would arrive at a piece inside the stone that could no longer be broken. -
400
Democritus of Abdera: Atomic Theory of the Universe.
“Matter was made up tiny individual particles called atoms. Atoms could not be created, destroyed or further divided".
It was not based on experiments, but on logical reasoning. Democritus is considered the father of the atom, he was a close contribution to what we currently consider correct.
Aristotle rejected it, he claimed that matter was continuous or seen as a whole, contrasting with the idea that matter was made up of tiny indivisible particles. -
John Dalton: Solid Sphere Model
This model provided the first insight into why chemicals react in fixed stoichiometric ratios and why two or more types of atoms come together to form compounds.
It was wrong for... Atoms aren´t indivisible, they are composed from subatomic particles. -
John Dalton: Solid Sphere Model
"Atoms are indivisible, those of a given element are identical, and compounds are combinations of different atoms" -
J.J. Thomson: The Plum Pudding Model
Thomson's conclusions were bold: cathode rays were made of particles he called "corpuscles," and these came from inside the atoms at the electrodes, meaning that the atoms are divisible.
However, his model made incorrect predictions about the distribution of positive charge within atoms and left the regularity of Mendeleev's periodic table unexplained. -
J.J. Thomson: The Plum Pudding Model
A spherical-shaped atom composed of a uniformly distributed positive charge on which individual negatively charged electrons resided; atoms are neutral, so the sphere contains equal amounts of positive and negative charges.
Three experiments were carried out using cathode ray tubes, in the first instance it was shown that electric fields were capable of generating the deflection of these.
Following the same studies and experiments, in 1897, Thomson discovered a new particle called an electron. -
Ernest Rutherford: Nuclear Model
The planetary model of the atom failed to explain why individual atoms produce discrete line spectra. In fact, according to Rutherford's model, each individual atom should produce a continuous line spectrum. Also, the electrons orbit the nucleus in a circular fashion. If this was true, then as electrons accelerate around the nucleus, which would imply that the electron would continually lose energy. -
Ernest Rutherford: Nuclear Model
The atom, as described by Ernest Rutherford, has a tiny, massive core called the nucleus. The nucleus has a positive charge. Electrons are particles with a negative charge. Electrons orbit the nucleus. The neutron had not been discovered when Rutherford proposed his model, which had a nucleus consisting only of protons. James Chadwick noted that because the neutrons had no charge, they penetrated much further into a target than protons would. -
Niels Bohr: Bohr Model of the Atom
The model was wrong because...
• Since electrons are very fast, they must require not only in classical physics but also in relativity theory.
• The Bohr atomic model can only explain the spectra of single-electron atoms.
• The wave-particle duality was not taken into account in Bohr's atomic model.
• The concept of "orbit" is wrong.
• It doesn't mention neutrons. -
Niels Bohr: Bohr Model of the Atom
The Bohr model states that atoms have different electronic configurations in which the electrons move in circular orbits around the nucleus.
In 1913, Niels Bohr highlights Bohr's theory using the spectral lines of the hydrogen atom and Planck's quantum theory.
His quantized model of the atom explained how electrons can have stable orbits around the nucleus. Besides that, he realized that to build a satisfactory atomic model he had to somehow include the Planck-Einstein quantum of energy. -
Erwin Schrödinger: Quantum Mechanics
The model was wrong because...
-It does not consider the relativistic effects of fast electrons.
-The model also does not consider electronic spin.
-Finally, this model cannot explain why an electron in an excited quantum state can decay to a lower energy level if there is one free. -
Erwin Schrödinger: Quantum Mechanics
It is the quantum mechanical model of the atom based on the Schrödinger equation. With this formula, the probability of finding an electron at a certain point in an atom could be known. Schrödinger claimed that electrons could also rotate in more complex elliptical orbits and calculated relativistic effects. Currently, there is no more precise model of the structure of the atom, which is why we also refer to it as the current atomic model.