Evolution of the Atom Model

Democritus

400 BCE

First atomic model.
Stated that the universe was composed of two elements: the atoms and the void in which they exist and move.
Stated there was an infinite number of atoms and that they can’t be destroyed, they differ in size, size, and temperature, are always moving and are invisible.

Dalton

1803

It was proposed by John Dalton.
It proposed that all matter was composed of atoms, indivisible and indestructible.
Atoms of the same element were identical but atoms of different elements had atoms differing in size and mass.
All compounds were composed of combinations of these atoms, and chemical reactions resulted in the rearrangement of the reacting atoms.

Thomson Experiment

1897

In 1897 JJ Thomson discovered the electron using the cathode ray experiment. This experiment consists on turning the power on and letting the particles pass through the tube. Thomson used a fluorescent screen so he could see the beam. Knowing the a magnet has a positive and a negative side as he drew it closer to the tube with the negative side it repealed and as he drew it closer with the positive it attracted. With this he discovered there were negative particles called electrons.

Thomson Publication

1904

In 1897 Thomson made his discovery using the previous shown experiment. In 1904 he published his discovery and model the atom. He stated that atoms were made of electrons that were surrounded by a positive charge. That means that electrons were negatively charged but were floating on a positive charge.

Rutherford

1911

Ernest Rutherford proposed his model in 1911 using the "Gold Foil Experiment". This experiment consists of shooting alpha particles which are positive onto a gold foil and they expected the particles to go straight through the gold foil. He saw the particles were all over the place that led him to the conclusion that there is a positively charged particle in the middle of the atom which he called nucleus. He stated that the atom was mostly empty space with electrons orbiting the nucleus.

Rutherford-Bohr

1913

Niels Bohr proposed his model in 1913. It was a modification of the Rutherford model, he agreed in everything with Rutherford but added some things. He proposed that electrons orbited the nucleus on separate orbits that had a set size and energy for the electrons, and that the lowest orbit is the one with the lesser energy. He added also that the number of electrons orbiting an atom determine the properties of an element.

Quantum Mechanical

1926

It was proposed in 1926 by Erwin Schrödinger. This model was based on mathematics. It was based on the quantum theory which proposed that matter has properties associated with waves. It used complex shaped of orbitals in which they might be an electron. Schrödinger said that you couldn't know the exact position of an electron, this theory consists in predicting the location of the electron without being exact.