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400 BCE
Democritus
Description of the model: stated that matter consists of invisible particles called atoms and a void. His atomic model was solid, and stated that all atoms differ in size, shape, mass, position and arrangement, with a void between them.
Experiment: Democritus knew that if you took a stone and cut it in half, each half had the same properties as the original stone. -
400 BCE
Democritus atomic model
Contributions: he used the word atom for the first time, everything is composed of atoms, which are physically but not geometrically indivisible and between atoms and empty space.
How was it wrong?: it was not specific, and he did not discovered that there were subatomic particles like protons, electrons and neutrons. -
Jhon Dalton
Description of the model: he defined an atom to be a ball- like structure, as the concepts of atomic nucleus and electrons were unknown at the time. His model was the result of the conclusions of several experiments they performed with gases.
Contributions: Matter is made up of atoms that are indivisible and indestructible. All atoms of an element are identical. Atoms of different elements have different weights and different chemical properties. -
Dalton's Model
Atoms of different elements combine in simple whole numbers to form compounds. Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged.
In Dalton's model, different atoms should be different in all respect which was proved wrong by isobars.
How it was wrong?: According to this model, all the atoms of a given element are of same mass and density which was also proved wrong with the discovery of isotopes. -
J.J. Thomson
Description of the model: Showed an atom that had a positively charged medium, or space with negatively charged atoms inside de medium. -
Plum pudding model
Contribution: Tried to explain two properties of atoms then known.
How was it wrong: Thomson argued that there was empty space between the electrons.
How it was wrong?: Thomson argued that there was empty space between the electrons. -
Rutherford model
Contributions: discovered alpha and beta rays, set forth the laws of radioactive decay, and identified alpha particles as helium nuclei. Most importantly, he postulated the nuclear structure of the atom.
How it was wrong?: he couldn't explain why negatively charged electrons remain in orbit when they should instantly fall into the positively charged nucleus. -
Ernest Rutherford
Describe of the model: shows that an atom is mostly empty space, with electrons orbiting a fixed, positively charged nucleus in set, predictable paths. -
Niels Bohr
Description of the model: Niels Bohr proposed the Bohr Model of the Atom in 1915. The Bohr Model has an atom consisting of a small, positively charged nucleus orbited by negatively charged electrons.
Contributions: Bohr was the first to 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.
Radiation is absorbed or emitted when an electron moves from one orbit to another. -
Rutherford-Bohr Model.
How was it wrong?: The Bohr Model contains some errors, but it is important because it describes most of the accepted features of atomic theory without all of the high-level math of the modern version. It violates the Heisenberg Uncertainty Principle because it considers electrons to have both a known radius and orbit. -
Quantum mechanical model
Contributions: He was awarded the 1933 Nobel Prize in Physics, along with British physicist P.A.M. Dirac, and later became a director at Ireland's Institute for Advanced Studies.
How it was wrong?: it is according to quantum theory, and it's impossible to know the exact position and momentum of an electron at the same time. -
Erwin Schrödinger
Description of the model: the atom was believed to be composed of a positively charged nucleus surrounded by negatively charged electrons.
