The Physics Of The Atomic Theory

Democritus of Abdera was a greek philosopher born around 460 BC, a cheerful and blissful man. He was one of the two founding fathers of the Atomic Theory. His thought process on the theory, was that matter was comprised of tiny building particles called atoms. This theory was widely questionable at this time. As people were not very well accustomed with accepting new ideas, and/or new concepts of philosophy and science. This theory was only partially correct, and as scientist of the more modern age began to look deeper into Democritus’s work, they begin to make new theories and hypothesize new ideas about the atom. Which later on, would lead to the development of the atomic theory and the most accurate description of the atom with the work of Niels Bohr.

The history of the atomic theory is thoroughly extensive. It had all started around 400 BCE when few people believed in an atomic theory, that atoms are building blocks. Democratic believed matter was made up of tiny particles. He called them atomos. Democratic is Leucippus’ most infamous pupil Later in history, the law of definite proportions was discovered. Two samples of given compounds are made of the same elements in exactly same proportions by mass regardless of the size or sources of the samples. After this came the law of conservation of mass and law of multiple proportions. Around 1808, John Dalton came up with a different atomic theory. He used Greek concept of the atom and all of the laws previously mentioned to acquire his

He stated that this was a mysterious force but never continued his research on it. Then in 460 B.C. there was a philosopher named Democritus. Democritus and his mentor Leocippus posed the question that if he broke bread into multiple pieces how many would breaks would it take until there was no more bread. He then was able to make a few theories being all matter was created of atoms and atoms are solid but not invisible. However, there was a man named Aristotle and many other philosophers who disagreed with Democritus and said matter was composed of four main elements. Earth, fire, air, and water. For example, a liquid was made of water and a stone was made of rock. Therefore, Democritus’s theory “ was rejected by Aristotle, one of the most influential philosophers of Ancient Greece; and the atomic theory was ignored for nearly 2,000 years.”(

Throughout history, science has been evolving and changing in a variety of ways. A vast number of proclamations have been both proven and disproven over time. An example of an ever-changing statement is the Atomic Theory of Matter. This theory states that matter is composed of extremely small units called atoms, what those atoms are made of, and what they do. This theory dates back all the way to ancient Greece and was most recently updated in the 1920's. Five main scientists have had a part in shaping and evolving this theory. They are Democritus, John Dalton, Joseph John Thomson, Ernest Rutherford, and Neils Bohr.

Ernest Rutherford was a New Zealand born British physicist who is famously known for “splitting the atom.” His work on the gold foil experiment contributed greatly to the model of the atom and helped develop the standard model of the atom to what we now use today. Without his contributions we would still be using the Plum Pudding model, an out dated and incorrect model, and we would have less of an understanding of how atoms form the world around us.

Before the First World War, German scientists James Franck and Gustav Hertz conducted experiments where they added electrons to Mercury atoms. They traced the energy changes that the collision caused. That experiment led Nils Bohr to make a theory that an atom can absorb energy in precise and definite amounts. After that experiment, many other scientists conducted research on radioactive methods to chemical problems and conducted more experiments on how elements would react when elements

He was the first to find how much an atom weighed. Amedeos findings were completely ignored up until a scientist by the name of Stanislao Cannizzaro. Cannizzaro presented Avogadro's findings four years after amedeo's death. Even after he presented other scientists still rejected the

Thomson4 discovered the electron3 using a cathode ray4. In a cathode ray an electric current is passed through a discharge tube5 which causes a glowing light that, Thomson concluded, was made up of smaller particles. He then discovered that these particles had a negative charge and were actually electrons. Thomson knew that electrons had a negative charge and believed that matter must have a positive charge as well. From the knowledge he accumulated, he formed a model of what he believed the structure of the atom looked like. This model has come to be known as the Plum Pudding Model4. In 19004 a professor of theoretical physics, Max Planck4, discovered that when you vibrate atoms strong enough you can measure the energy. Planck called these packets of energy quanta. At the time, physicists believed that light consisted of waves. Albert Einstein4 concluded that the quanta behaved like discrete particles. For many years there was a controversy on whether light consisted of waves or particles. In 1911 Ernest Rutherford4 bombarded atoms with alpha rays. Rutherford used Radium as the alpha particles4 and shined them onto gold foil. This was called the Gold Foil Experiment4. The conclusion from this experiment was that positively charged matter scattered the alpha particles and that most of the space4 around these positively charged centers has nothing in it. Furthermore, Rutherford thought that electrons must exist somewhere within that empty space and that they orbited a positive center, like the planets orbit around the sun. Rutherford also speculated that atoms consisted of a compact positively charged nucleus4 as well as that most of the atom’s mass is contained in the nucleus. In 1919 Rutherford finally identified the particles of the nucleus as discrete positive charges of matter and named them protons4. He developed a model of the atom but, due to the theory of electricity and magnetism, it was predicted, according to this model,

In many ways, Niels Bhor’s model modified the atomic structure that was initially proposed by Rutherford. Rutherford had proposed that electrons circled the nucleus like planets around the sun,

- He also proposed that negatively charged electrons were scattered around the nucleus, and these electrons were held in orbit by the nucleus because of electrical forces

Niels Bohr was the individual who discovered atomic orbitals. Bohr proposed that electrons travelling around the nucleus could only occupy orbits that had fixed energy values. He also proposed that atoms do not emit or absorb energy (when in its stationary state). It was Bohr whose work led to the planetary model of the atom and who accurately predicted the line spectrum of the hydrogen atom. The planetary model of the atom shows electrons orbiting the atom’s nucleus in circular paths (fixed) - just as the planets do around the sun. Though Bohr’s model retained some features of Rutherford’s model, Bohr’s model imposed certain restrictions on where electrons moved (anywhere around the nucleus’

Niels Bohr greatly contributed to the modern atomic model. He provided great knowledge on the atom and physics. He is considered to be one of the greatest physicists of all time because of his contributions to the atomic model. This required the help from a few of his fellow physicists, such as Ernest Rutherford and J.J. Thomson. Niels Bohr created the Bohr model in which he built his ideas from Rutherford and Thomson to create what he thought the atom looked like. Bohr believed that the middle of an atom is a positively charged nucleus with electrons surrounding it. He also discovered that the electrons were not in a specific orbit around the nucleus instead, they jumped around depending on the amount of energy they had.

Bohr was called upon by a fellow colleague named Ernest Rutherford, to help him solve some problems with the Rutherford Planetary Model of the atom. Bohr quickly took the position to help and new that the problem had something to do with the discharge of hydrogen within an atom. After solving this problem and coming up with his own law and model of the atom. This advancement changed physics forever. Bohr’s model was made up of four ideas.

He learned that it is impossible to find out where the electron is in an atom, he also constructed a cloud of an atom.

During Marie's time, the atom was thought to be the smallest particle in existence. At first, Marie and Pierre Curie believed that perhaps the atom was covered with cosmic rays. Marie tested numerous elements to find if other ones than Uranium would make the air conduct electricity better.