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500 BCE
Democritus
Democritus believed that all matter is made up of imperishable things called atomos, which is where we get the word atom. -
500 BCE
Heraclitus
A philosopher names Heraclitus believed that everything was made up of fire. -
350 BCE
Aristotle
Aristotle believed that everything was made of four different elements. Those were fire, air, water, and earth. He was revolutionary in the way that he guided us to our beliefs today about the periodic table and its elements. -
Dalton
Dalton created an atomic theory composed of these ideas;
1. All matter is made up of microscopic particles called atoms.
2. All atoms of one elements are all the exact same, and atoms of different are the exact same. (not the same between different elements.
3. Atoms cannot be broken, created, or destroyed.
4. Atoms of different elements combine in simple ratios to make chemical compounds.
5. In chemical reactions, atoms are combined, separated, or rearranged. -
Thomson pt 1
Thomson created a called a cathode ray that pretty much shot electrons through a tube showing a light. When doing this, he added magnetic plates to the sides and the light bent towards the positive charge, meaning the light had a negative charge. At this time,we did not know what electrons were and he changed that. This was a dramatic change because they discovered the charges of atoms and how they worked. This added to Dalton's theory because it added that there were charged to atoms. -
Thomson & The Plum Pudding Model
With finding that there were negative charges in atoms, he knew there must be positive charges to balance the electrons out. This lead to Thomson to create the Plum Pudding Model which described that there were just electrons floating around in a soup of positive charge. He showed this by making a Plum Pudding Model which showed the electrons in a mass of positive charge and it was made named because it looked like a plum pudding desert. -
The effect of The Gold Foil Experiment
Before the experiment, we thought that the atom was negative charges in a positive charge soup. This changed our thought of the atom because it made them think that most mass is in the nucleus of an atom which is positively charged, and the rest of the atom is negative. This changed Thomson's theory because he believed that first, the atom was even and the atom was mostly positive but with small negative parts to cancel them out. -
Rutherford & The Gold Foil Experiment
In 1899, Ernest Rutherford tested an experiment called the Gold Foil Experiment. What he did was he had alpha particles that were shot at foil. He assumed that weight was distributed evenly throughout the atom. when he shot these alpha particles they all went past the foil other than a couple that bounced back. What this showed about the atom was that the weight was distributed unevenly throughout an atom. -
Bohr and the Bohr Model and Experiment pt 2
In this experiment, he realized that the color was only certain colors. Because they first assumed that electrons could move anywhere, then there could be any color, but there was not.He used a line emission spectrum to look further when the lights were on.He noticed that every single atom had a different spectrum. He found that the electrons were not just moving where ever they wanted, but they were actually in a cloud. Bohr changed Rutherford's findings that it was just a soup of negative. -
Bohr and the Bohr model
In 1913, Bohr did the Bohr experiment. What he did was he predicted that electrons could have any color or light because the electrons were just moving all around the atom. How he did this was he produced electricity through a glass tube. What happened was it produced light. The reason that this produced light was because the electricity made the electrons excited. The electrons moved from their normal spot and when they went back to their spot, they released energy in the form of light. -
Schrodinger and the Electron Cloud Model
In 1926, Schrodinger found that electrons don't actually orbit, like first thought by Bohr. He said we don't know exactly where the electrons are outside the nucleus but it doesn't really matter. We know the estimated area but not the exact placement. The only thing that matters is the energy given off by the electrons and that is based on how far away the electrons are from the nucleus. The farther they are, the more energy they will have. -
Chadwick and the Electron Model 2.0
In 1932, James Chadwick did an experiment to find out what gave the extra mass that was not the protons. The electron had nearly no mass so he knew that there was something else. He tested an experiment that he shot alpha particles to hit pieces of medal and from that he discovered that there were neutral subatomic particles. Schrodinger discovered the different energy and color spectrum for atoms while Chadwick found that there were neutrons.
