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A brief look at the history of the atom

Updated on September 20, 2011

If you break a piece of matter in half, and then break it in half again, how many breaks will you have to make before you can break it no further? This is the question Democritus, a Greek philosopher, asked back in 460 B.C. He thought that there must be a smallest bit of matter. So Democritus called these particles of basic matter atoms.

Due to no other Greek philosophers taking it up and being interested in what Democritus had discovered, it was then more than 2000 years before anyone decided to carry on and explore this matter. It then wasn’t until the start of the 19th century, that John Dalton, an English chemist, put forward his ideas to do with atoms. From Dalton’s observations and experiments he believed that atoms were like tiny hard balls. In chemical reactions he also discovered that the atoms would combine with other atoms and rearrange themselves.
He said that all matter is composed of atoms, along with each chemical element having it’s own atoms that differed from each other in mass. With Darlton also finding out many other rules about atoms.

J.J Thomson's 'Plum pudding' model
J.J Thomson's 'Plum pudding' model

J.J Thompson

Then during the 19th century Thomson discovered electrons, this negatively charged particle turned out to be much smaller than any atom, as it would take 2000 electrons to weigh the same as the lightest element hydrogen.Thomson knew that electrons had a negative charge and thought that matter must have a positive charge. So he made a model of an atom called ‘plum pudding’ model, as it looks like pudding with raisins stuck in it. His model shows the negative electrons and positive matter, which he discovered.

Rutherford's atom
Rutherford's atom

Ernest Rutherford

Unexpectedly in 1911, Rutherford’s results became interesting when he bombarded atoms with alpha rays. He shined them onto atoms of gold foil and found that some particles bounced off the foil and back in a different direction and some going straight through the foil. Rutherford then concluded and thought that like the planets in our solar system the electrons must be orbiting around the dense nucleus, which is the centre of the atom. He found that the nucleus had a positive charge with the negatively charged electrons orbiting around the outside.

Niels Bohr diagram
Niels Bohr diagram

Niels Bohr

In 1914 Bohr came up with the next big discovery and came up with two big important rules:

  • Electrons can orbit only at certain allowed distances from the nucleus.
  • Atoms radiate energy when an electron jumps from a higher-energy orbit to a lower-energy orbit. Also, an atom absorbs energy when an electron gets boosted from a low-energy orbit to a high-energy orbit.

He then quoted ‘ that these rules seem impossible, but they describe the atoms operate. So lets pretend they are correct and use them.’

With no one being able to explain after some time of knowing that the light given out when atoms were heated always had specific amounts of energy, Bohr suggested that the electrons must be orbiting the nucleus in different energy levels called shells (As shown in diagram).This energy must be given out when 'excited' electrons fall from a high energy level to a low one.

Still today we use the these theories stated from these scientists and has been greatly investigated over the past two centuries and still investigated to this day.

Below is a cool video I found which is worth checking out showing you how sodium reacts when mixed with water!

Exploding sodium


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    • point2make profile image

      point2make 5 years ago

      An interesting look at the history of the atom. I enjoyed your hub and learned a few things as well. Thanks

    • marstoblog profile image

      marstoblog 5 years ago from Hitchin, England

      thank you I'm glad you learn't something!

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