Atomic Theories

Theories on the structure and behaviour of atoms have been evolving for more than two millennia. The following are key theories introduced by important individuals who have shaped the ideas of physical world to what they are today.

Democritus Postulates Atoms as "Indivisible Particles"
Around 400 BC, a Greek philosopher and early scientist by the name of Democritus theorized that all matter is made up of atoms. He described atoms as the smallest particles of an element that retain the chemical identity of that element. While this is only a conceptual view, it was one of the first to challenge the ancient perspective of all matter being composed of Earth, Wind, Fire and Water. It may have lacked certain scientific evidence but it acted as a base theory for following generations in science to build upon.


Antoine Lavoisier Pioneers the "Law of Conservation of Mass"

As the name of his theory suggests, the French nobleman suggested during the eighteenth century that mass is conserved in a chemical reaction. He explained that chemical reaction neither produce mass or destroy mass. Lavoisier's theory was later included in that of John Dalton's as described later on. 

Joseph Proust Form's "Proust's Law"

Another Frenchman, it was in the late eighteenth century that Proust created a Law of Constant Composition also known as the eponymous "Proust's Law." He theorized that a given compound always contains the same elements in the same proportion by mass. Essentially this law of definite proportions claims that water will always include 89% oxygen and 11% hydrogen regardless of the amount of molecules found in any sample. 

John Dalton's "Atomic Theory of Matter"

This monumental hypothesis of John Dalton borrowed from earlier theories to develop what was the most definite and conclusive postulation of the time. It was based in the following: 

• Each element is composed of extremely small particles called atoms. 
• All atoms of a given element are identical, but they differ from those of any other element. 
• Atoms are neither created or destroyed in any chemical reaction (Lavoisier's Law of Conservation of Mass) 
• A given compound always has the same relative numbers and kinds of atoms (Proust's Law of Constant Composition)  

J.J Thomson's "Raisin Bun" Model

In 1897, Thomson took John Dalton's ideas to a new level. He added an extra component in electrically charged particles. He implicated this into a "Raisin Bun" similar to atoms being solid spheres made-up of a solid positive mass (or core) with tiny negative particles embedded in the positive core. These positive particles became known as protons while the negative charged ones are called electrons.  

Ernest Rutherford's Planetary Model

Studying under J.J. Thomson, Rutherford became very familiar with the Raisin Bun model and used a famous experiment to make detail examinations on the composition of a atom. It was his "Gold-Leaf Experiment" which proved that the nucleus is a positively charged for core of the atom which holds protons and neutrons. Neutrons have no charge. Existing outside of this nucleus was a great deal of empty space housing spinning rings of electrons. 

Each of these theories have contributed to how we see the world today. They took us from conceptual knowledge of the physical to a tangible and scientific one. To learn more, and see a chart organizing the above information, feel free to click here.  

-Simon Sierra