For many years scientists all over the world have been wondering what the smallest things in our world are. In my essay I will be walking you through the evolution of the atomic model & the discovery of radioactivity.
One of the first atomic models was created by Democraticus at around 400BC. He created a theory of the atom which he called atomos, the Greek word for uncuttable, (a being prefix meaning not & tomos meaning cut), by reasoning logically that if you cut a stone in half, the two halves would still have the same property as the whole rock. Democritus also thought that there must be a limit to cutting in half the rock since at one point the pieces would be so small it would be impossible to cut them in half again, hence the name. Democritus speculated that atoms existed in many different shapes & sizes. Democritus was right on the points that atoms are small & have the same properties as the substance they are part of.
The atomic theory was later further developed by John Dalton, born in 1766 in Cumberland, England. John Dalton is often considered the resurrector of Democritus's model which he further developed into one of the first modern atomic theories. He published his atomic theory in 1808 . Dalton’s model states that all matter is made from atoms. Also Dalton said that all the atoms from any one element are identical in properties & mass. Just like Democritus, Dalton thought that atoms are not divisible & indestructible hence eternal. Dalton's theory states that when a chemical reaction is triggered atoms are combined, rearranged or split & that when combining two or more different types of atoms you create a compound. Dalton’s theory rightly stated that different elements have different atoms but was wrong about atoms being indivisible.
In the development of the atomic theory Joseph John Thomson, born on the 18th of December, 1856, played a very important role. He is known as the plum pudding scientist from the name of his atomic theory which states that electrons are imbedded in an atom like plums in a plum pudding. Thomson revolutionized the atomic theory thanks to the discovery of the electron, the first subatomic particle, while experimenting with a Crookes in 1897. Since atoms are neutrally charged but only the negative charges had been discovered by himself, Thomson wondered how the positive charges are distributed in an atom. Thomson speculated that the positive charges were located equally throughout the atom with the electrons inside the positive charge. Thomson’s model rightly recognized the electrons as part of the atom, with a highly complex structure. This proved the ideas of atoms being homogeneous wrong. Thomson failed to recognize that the positive charges in an atom are present as the nucleus.
Ernest Rutherford was born on August 30, 1871 in Brightwater New Zealand. Rutherford, a former student of J.J. Thomson, proved his own teachers’ plum pudding model wrong with the gold foil experiment which he carried out multiple times from 1909-1911 .In the experiment Rutherford pointed alpha particles (helium nuclei also often found in uranium containing rocks) at gold foil & recorded where the particles passed through the foil. Rutherford recorded that the alpha particles passed through most of the gold foil, some were deflected at an angle or ricocheted back bringing Rutherford to the conclusion that there must be a dense positively charge at the center of an atom: the nucleus. This contribution got Rutherford the nickname: the man who split the atom. Rutherford discovered that certain substances emit different types of radiation & called them alpha & beta. Rutherford was correct about there being a positive charge in the middle of an atom but didn’t explain why electrons move around the nucleus.
Niels Bohr was born on October 7 1885, in Copenhagen, Denmark Niels Bohr was a student of Ernest Rutherford & developed his own model of the atom in 1913 in which suggested the following points:
Electrons only move in certain orbits & move between orbits by jumping. For example, an electron that is in the ground state gets excited by energy, jumps from its ground to the higher energy orbital from which it then slowly falls back down as it loses energy due to gravity.
Each orbit has an energy that depends on how close the orbit is to the nucleus. The closest orbit to the nucleus is E1, then comes E2 & so on.
Energy is used when a jump from a lower state such as the ground state to the excited state happens energy is absorbed & as electron returns to its lower orbit the energy is released
The energy released as an electron returns to its lower orbit can be calculated.
Bohr's Model is also known as the planetary model due to the fact that just like the planets in our solar system in Bohr's model the electrons orbit around the nucleus of the atom. Bohr rightly proposed the orbits for the electrons movement around the nucleus but didn’t realize that energy could be emitted by moving electrons.
An important contribution to our knowledge about electrons movement was given by Erwin Schrodinger, born on August 12, 1887 in Vienna Austria. Schrodinger was inspired by the Heisenberg uncertainty principle to create a complex procedure that can be used to calculate where electrons are when the are exited with a certain amount of energy. He stated that electrons don’t move in paths that act like tracks for trains but rather in waves. According to his theory, the exact location of the electron is impossible to be defined. Schrodinger was certain that it was possible to calculate areas where the probability of finding an electron is higher. He called these areas clouds. Just like Bohr, Schrodinger said that electrons move between clouds by absorbing or releasing quantum energy. Schrodinger's’ theory is still widely recognized as the correct model of the atom.
Marie Skłodowska Curie was born on November 7, 1867 in Warsaw, Poland. In 1897 Marie decided to get a doctorate in physics for which she put her focus on learning more about the mysterious rays produced by the element uranium. Curie found out that the amount of rays produced by uranium were directly affected by the size of the sample she was working with. Furthermore she discovered that even the alteration of the uranium didn’t affect the rays emitted from it. Marie Curie later discovered that the amount of rays emitted are directly affected by a strong unknown element found inside the uranium. Together with her husband Pierre she identified two new elements which they called Polonium & Radium with radium being the element characterized by the higher strength energy rays than Polonium. Marie Curie was the person to name the high energy rays emitted from certain substances radioactive.
James Chadwick was born on October 20th, 1891 in Bollington, England. In 1932 James Chadwick found out that the beam discovered by Irene Curie, created when shooting alpha particles at beryllium was made out of particles that matched the size of protons. He also discovered that neither magnetic or electric fields could deflect or influence the trajectory of these particles. Chadwick deduced that the particles that made up the generated beam were made up of neutral particles which he named neutrons. Thanks to Chadwick today we know that neutrons & protons make up the nucleus of an atom.
Even thousands of years ago ancient scientists were trying to figure out what the earth was like on a microscopic level. This is a question that despite of our technological progress we are still not able to answer with 100% sureness. The accepted atomic theory will most likely still keep changing with new discoveries & the development of new technologies. It is key to understanding the small things in our universe since the changes they affect are big. This is what it was like in the past, as the theories of the scientists in my essay prove.