Understanding the Atom with Many Scientific Theories

Introduction

Our understanding of the atom has changed over many periods over time. Through experiments and observations, evidence over the years has supported scientists to create theories. A philosopher named Democritus made the first theory in 470-380 B.C. Following this first theory, many improved models where created. These are Dalton’s theory, Thomson’s theory, Rutherford’s theory, Bohr’s theory, Heisenberg’s theory and todays modern model. The current day atomic model that most scientists use is Bohr’s model. Throughout this report, I will be explaining how each atomic model works and showing a diagram of how it looks.

John Dalton’s Theory

John Dalton was an English chemistry teacher who laid the groundwork’s for todays atomic model. Dalton based his theory on two laws: the law of conservation of mass and the law of constant composition. The law of conservation of mass says that matter is not created or destroyed in a closed system. In 1808 he suggested four main ideas: First, he proposed that all matter is made of atoms and that atoms are indestructible. Secondly that the atoms of different elements vary in size and mass. Thirdly, combining atoms forms compounds. Furthermore, all atoms of the same element are identical and that atoms are indestructible. Dalton’s model has been discarded, as at that time he didn’t know about electrons and protons, he thought an atom just looked like a small, solid sphere. The modern atomic theory is a little more evolved but Dalton’s theory became the theoretical foundation for chemistry.

Thomson’s Theory

Thomson was an English physicist widely credited for his identification of the electron. It was evident that Thomson was extremely interested in the atomic structure. While living in America he discovered a method using positive through this method Thomson discovered electrons and noticed that an atom can be divided. He also concluded that atoms are made of positive cores and negatively charged particles (electrons) within it. Before the nucleus was discovered, Thomson called this the Plum Pudding Model. The model shows that a “pudding” of positive charges to balance the negative charges surrounds the electrons. Due to his great work at the time, Thomson was awarded a Nobel Prize in Physics and a Royal Medal.

Rutherford’s Theory

Ernest Rutherford was a New Zealand born English physicist. Today he is regarded as the father of nucleus physics. It all started with numerous tests and experiments in his lab at the University of Manchester. Rutherford and his team used a method that involved alpha particles. Rutherford directed the famous Geiger–Marsden experiment in 1909 that proposed (upon 1911 analysis), a new atomic model. This model has further developed our understanding of the atom. It suggests that the atom is a dense, tiny, positively charged core called a nucleus. In the nucleus are what he called protons (positively charged particle) and neutrons. and surrounding it are the electrons. They circulate at some distance, much like planets orbiting around the Sun. The discovery of electrons and nucleus was groundbreaking. In fact, the Rutherford model replaced the “plum-pudding” atomic model of J.J Thomson (paragraph above). In which the electrons were embedded in a positively charged atom like plums in a pudding.

Bohr’s Theory

Bohr was a physicist born in 1885. Unlike the previous physicists, Neils Bohr wasn’t an English man he was in fact Danish. Bohr believed in the idea of electrons existing around the nucleus (Rutherford’s model) but however at that time he was questioning why the orbiting electrons did not spiral towards the nucleus. He thought this especially since the nucleus is positive and the electrons are negative, they will attract to one another (due to the Coulomb force). He used experiments with different gases to create a new model. In 1913 he proposed that there are electron shells around the nucleus and they have different amounts of energy depending on their distance away from the nucleus. He tested this, as the atoms would emit light when the electrons jumped to different shells. Bohr also believes that there is a formation for the electron shells. This is shown in the diagram below. His model is revolutionary and is the most used and referred to diagram today. He was honored with a Nobel Prize for physics.

Heisenberg’s Theory

Werner Heisenberg was a German born, theoretical physicist. His profuse knowledge of quantum mechanics helped him produce a new theory. He went against Bohr’s theory, as he believed that the electrons surrounding the nucleus do not travel in orderly orbits. Heisenberg’s contribution to the atomic theory was made when he was calculating the behavior of electrons and the subatomic particles that make up an atom. At 23, in 1932, Heisenberg used mathematics into understanding the patterns of an atom's electrons. Werner's discovery helped clarify the modern view of the atom because scientists can compare the actually few numbers of atoms there are, by their movements of electrons, and how many electrons an atom contains. Surrounding the outside of the nucleus is what he called and pretty much invented the electron cloud, which is a name given to the electrons that are widely spreading and moving around.