Atomic structure was originally devised by ancient Greek philosophers; However over recent years this theory has been modified and changed by many different scientists, such as Dalton, Thompson, Rutherford, Bohr and Chadwick.
In 1808 John Dalton in his book “new systems of chemical philosophy.” Proposed that elements are composed of many discrete and invisible particles which are called atoms, atoms of the same element have identical properties and atoms of different elements have different properties. Compounds are composed of atoms of more than one element and also that a chemical reaction involves the separation, combining or rearranging of atoms. He was also responsible for part of the periodic table, as it was he who introduced the idea of chemical symbols, being the first to discover carbon dioxide.
In the late 1800s and early 1900s J. J. Thomson conducted some experiments that did not agree with Dalton’s earlier atomic theory. He performed experiments using a Cathode ray tube. He conducted electricity through gases, causing a glow to be seen at the furthest end of the cathode tube. This proved that cathode rays must be made of something which has a negative charge. Thomson then concluded that atoms have tiny particles inside them called electrons which have a negative charge. He knew that on the whole atoms were neutral, so he came up with a theory that there must be a positive charge within the atom which would balance out the charge of the negative electrons. He suggested the “Plum pudding” model; the idea that negative electrons were spread at random throughout the atom which also contained a positive charge. This would make the atom electrically neutral.
In 1909 Ernest Rutherford and his colleague Ernest Marsden embarked on another experiment called the “Gold Foil Experiment” This consisted of a piece of gold foil which was placed directly in the