In the year 1913, Niels Bohr tried to explain the Bohr atom model through an electron concept which follows an orbit circling the atom core which contains protons and neutrons. According to Bohr, there is only an orbit with a certain number, and the difference between one orbit and the other is the orbit distance from the atom core. The existence of electrons in the low as well as the high fully depends on the electron energy level. Therefore the electron in the low orbit will possess a smaller level of energy compared to the electrons in the higher orbit.
In the year 1910, Ernest Rutherford conducted an experiment to the truth of this model by conducting what is now known as the Rutherford scattering experiment.
Rutherford found the alpha particle, a particle emitted by a radioactive atom, in the year 1909. This particle possesses a positive charge, and the fact is that we now know that α-particle like the helium atom is released from its electron, giving a charge of 2+.
In this scattering experiment, the flow of α-particle is directed to the gold film. This gold film is selected by Rutherford because it could be made very thin—only as thick as several gold atoms. At the time the α-particle passes the gold film, Rutherford could measure how many α-particles would be scattered by the gold atoms by observing the sparks of light of the α-particle hitting the scintillator screen. Under the atom theory of Thomson, Rutherford had the hypotheses that the α-particle would be a little diverted, at the time the gold proton repelled the high positive charged α-particle.
In the early 1900s, J.J. Thomson proposed a new atom model which also takes in the presence of the electron and proton particles. Because the experiment shows that protons possess a mass far greater compared to the electron, the Thomson model therefore pictures the atom as a large single atom. In the proton particle, Thomson inserted electrons which neutralize the presence of the positive charge of the proton.
According to Thomson, the atom consists of a a positively charged sphere with an even charge density. In this positive charge are electrons spread out with negative charge with the same amount as the positive charge. The popular way in illustrating this model is to consider the electron as plumb raisons in a proton pudding , therefore the model was given the name plumb-pudding model.
In the year 1803, John Dalton an English physicist developed the concept of the first modern atom. The Dalton model gave its main attention to the chemical characteristics of the atom, on how the atom forms compounds, instead of trying to explain the physical characteristics of the atom.
The main concept of the Dalton model is as follows:
The basic concept of the atom actually has long been known by man. The concept among others originated from the thoughts of the old Greeks pioneered by Democritus who lived at the end of the 4th century and early 5th century Before Christ. According to the theory put forth, an object could be divided into very small pieces which finally could be divided no more which is called the atom. The word atom comes from the Greek word ”atomos” which means ”cannot be divided”.
