The 2,400-year search for the atom

Not until around 440 BCE, Democritus coined that each and everything in the world is made up of some sort of particles. These particles are surrounded by empty spaces and are known to be of different size and shape. The shape and size is entirely based on the substance that they uniquely compose. Democritus thus called these particles as atomos which is a Greek word meaning indivisible.


John Dalton And Aristotle

Aristotle declined Democritus theory. He said that matter is oriented from earth, water, wind and fire. Later to this theory of Aristotle, John Dalton who was a Quaker teacher challenged it. Unlike Democritus’ theoretical theory, Johns Dalton showed that those with common substances always break down into the same elements and that too in the same proportion.

He stated that the number of compounds is just the combination of atoms of various elements with each having a particular mass and a size. These masses and size could neither be created nor destroyed.

Discovery of Electron By J. J Thompson

After a century, a physicist, J.J Thompson discovered the electron. In the model of atom, J.J Thompson showed the atoms as uniformly packed spheres of positive matter which were filled with negatively charged electrons. This led Thompson to win the Nobel Prize. Later, his students made certain discoveries.

Ernest Rutherford-

Ernest Rutherford was one of Thompson’s students who later came to be known as the father of the nuclear age. He showed that most of the atoms consist of large empty space by conducting the below mentioned experiment.

  • When he was studying the effect of X rays on gases, he thought of scanning atoms even more closely than usual. He did that by shooting minute positive charged alpha particles at a sheet that is made up of a golden foil.
  • Talking about Thompson’s model, the atom’s thinly dispersed positive charge will not be as required so that the particles can be deflected at any one place. Here most of the particles pass through while some bounce back.

This suggested that the foil is a thick net like structure with a mesh. This led to Rutherford’s conclusion of an atom consisting of large empty space having few electrons. There was mass that was centered and was later known as the nucleus where the alpha particles bounced back.

Neils Bohr

Bohr decided on an expansion on Rutherford’s model. He drew on work conducted earlier by Max Planck and Albert Einstein; Bohr suggested that electrons orbit the nucleus at fixed distances and energies. They are capable of jumping from one place to another but they are not ought to exist in the space in between.

Werner Heisenberg Contradiction To Neil Bohr’s Theory

Later this theory of Bohr faced some complications implying that electrons behave like electromagnetic waves instead of being discrete particles. Thus they were not confined to a particular point in space. Further, Werner Heisenberg showed that supposing the exact position and speed of electrons is impossible. This gave rise to the current quantum model of the atom.

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