In the history of chemistry and physics, there were (are) lot experiments to find what is atom, what is the atomic structure and what are elements. Different models such as Democritus's atomic theory, Plato and Aristotle's atomic theory, John Dalton's atomic theory (1808) for atomic structure were developed and introduced with time by scientists. Some of these models were rejected and modified by time and we will see the history of finding of atom in this tutorial.
In the beginning, humankind passed several ages. Hunting era, pastoral age, and agrarian age (3000BC-4000BC) respectively.
When humans entered the agrarian age, they had plenty of time to carefully think and observe the environment. Then humans began to think about how these environmental activities run and what and how these are made. And also they found some pure elements (2000BC) like Au, Fe, S, and Hg because this element is less reactive than others and exist naturally pure stage. And also they observed some of these things converted to other things.
These main things they called "elements". That's how the word element came. And converted things they called compounds.
The second thing is ancient Greeks believed that there were four elements that everything was made up of, earth, water, air, and fire. This theory was suggested around 450 BC.
He said that matter is made up of very fine substances that are invisible to the naked eye. He said this without any investigation but he observed some incidents and they are mentioned below.
And he also said as matter breaks down, it reaches a point where it cannot be further divided. That thing they called "ATOMOS".
They say matters can be divided until infinity. Because of this, Democritus' opinion about atoms was undermined.
He said that again matters consist of small particles which are invisible naked eye (Democritus theory). But also he said the size and type of elements vary from element to element. Furthermore, he said that combining elements with other elements do not change their nature. It's just like a solid sphere.
When touching the dolomite that rubs our hand, Dyes disperse through water.
He did several experiments by using a Cathode ray tube.
When applying a high voltage between the cathode and anode he observed a green color beam travel from cathode to anode. And also when a close magnet is to the cathode ray tube the green color beam reflates oppositely. Magnet repulsion is negatively charged and attracts positively charged, they already know this phenomenon.
Accordingly that Thomson decided that the Stanger beam which starts from the cathode consists of or holds a negative charge. This is the first recorded incident about subatomic particles called "electrons". And he introduces the "plum pudding model". He simply said that negatively charged electrons are embedded within a positively charged soup (solid sphere).
He introduces quite a different idea about atoms. He said that atoms are not like a solid spheres. Hans Geiger and Ernest Marsden practically conducted Rutherford’s idea. Accordingly, in this experiment, a thin gold foil exposes to an alpha particle beam. And also that area was covered by the fluorescent screen which is sensitive to alpha particles.
Here most alpha particles passed straight through the gold foil. And some of the alpha particles were deflected by small angles. Surprisingly one out of every 12,000 alpha particles appeared to rebound. Accordingly that he stated a few statements about atoms.
Accordingly, these statements arise big problems for the science community. They accepted this model but Rutherford was unable to answer that questions/ problems.
Above questions were somewhat resolved by using the Bohr model. He introduced a theoretical model for the hydrogen atom that explained its emission spectrum. A gas discharge tube was used for this and discharge light was transferred to a Prisma and get the line spectrum. According to the observation. he said,
However, at that time scientists also have some questions,
Schrodinger was known as the savior of science society at that time. Because he introduces the Schrodinger equation. Before he introduces this equation, they already know that electrons have both particle and wave behaviors (accordingly to the double slit experiment).
This equation simply said that, of the considered electron,
If someone solves the Schrodinger equation he or she can get / ψ /wave function.
We believe that wave function describes how to behave that consider electron in the atom. But this phenomenon is still a mystery. Because of how electrons behave as a particle and wave same time. Accordingly, double slit experiment we observed, we observed some electrons, that behave as a particle and if we do not observe that same electron they behave as a wave. Schrodinger was also unable to describe, what is the real meaning of ψ.
After that Max Born said that, if we square Y we can get a probability density function. That function describes the areas we can catch some considered electrons. However, it does not say what is ψ. So the entire science world is still waiting for the solutions to this.