By: Brian Pichardo & Jose Sanchez

 Atoms are fundamental building blocks of matter and they make up every physical object that exists. That idea has not changed for thousands of years. An idea concerning the subject has though. That is the idea concerning the structure of an atom. These different ideas have changed from Greek Atomism to the current Electron cloud model.

 During the 5 th century Leucippus and Democritus proposed that everything was made of a small indivisible object called an atom.  Democritus argued that atom were made of the same material and atoms made up four fundamental elements. The elements were fire, water, earth, and air. If those four elements were mixed then any substance in the world could be created. It was the only theory on the atom during that time because the  Greeks did not have the materials nor the resources in order to do any real scientific experiments so all of that theory was based only on thoughts and some vague observations.

 During the early 1800’s John Dalton proposed a different view of the atom. Dalton learned that different compounds were made of different elements in whole number ratios. He learned that what the Greeks were proposing had some truth behind it.  By using scientific experiments. He learned that elements were pure because the atoms that made them up were exactly the same in mass. What differentiated elements were the difference in mass between atoms from two different elements.  Dalton’s model was just a simple solid sphere that was completely indestructible.  According to Dalton there was nothing smaller than an atom. Scientists would soon prove him wrong.

 The cathode ray experiments were a series of experiments that deduced the existence of the electron particle. These experiments were first used by J.J. Thompson.

 The plum pudding model was created after J.J. Thompson’s work with Cathode rays led to the discovery of electrons. The model disproved a part of Dalton’s theory on the atom since it proved that there was a particle smaller than an atom.  The plum pudding model is basically negatively charged electrons in a puddle of positive charge to balance out the atom. The electrons were arranged in rotating rings.

 This model of the atom was created by Ernest Rutherford after the discovery of the nucleus.  The nucleus was discovered by the same man’s experiment when he fired alpha particles at gold foil. Rutherford placed a radioactive source inside a lead shield and cut open a small opening that allowed the radioactivity to shoot out in a beam. The beam shot at a gold foil that had some particles reflected. If an atom was made up of only electrons then the beam would have shot through the foil completely. This meant that the atom had a bigger particle. This led to the discovery of the nucleus. The model had a nucleus and was surrounded by electrons that surrounded the atom in an orbital pattern.  This model had some problems though. Scientists found out that if the nuclear model was true then the electrons would spiral towards the nucleus. After scientist Niels Bohr fixed most of those problems he created the Bohr model.

 The most current model is the quantum mechanical model. It’s different from the orbital model in that the electrons are more free moving.  In 1924, French scientist, Louis de Broglie proposed that, like light, electrons could be both particles or waves. After that was proven Austrian physicist derived a set of equations on with this work done he was able to create the electron cloud model.  The model has a nucleus surrounded by a cloud of electrons. The closer it gets to the nucleus, the darker the cloud part of the model gets. This means that the darker it gets on the model the denser it is on the actual atom. If it is denser then the odds of finding an electron intensifies.

 Over time the atomic model has varied greatly after a scientist or scientists have discovered and fixed some flaws from previous models. From Greek atomism to a quantum mechanical model. If compared the difference is severely large. Only the fundamental idea of the atom still exists without much change. Over time the model has changed from minor tweaks to major changes. Chances are that in the future scientists will do the same to refine the model. They might even discover a new component of an atom. This also could lead to proof for the string theory. All of that is in the future but for now we can just reflect on the flaws from past incarnations of the model and hope to get to the truth behind an atom.