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Dalton theory was the first complete attempt to describe all atoms and their properties. he based his theory on the law of conservation of mass and law of constant composition

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Matter is made up of interacting subatomic particles. The subatomic particle is a nucleus of protons and neutrons, and a cloud of orbiting electrons.

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Atoms are indestructible.
took about two millennia for the atom to be placed as a solid fundamental chemical object by Dalton

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Rutherford's theory was that an atom has a positive nucleus with negative charges orbiting it.

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Rutherford shot alpha particles towards a gold foil sheet, he noticed that when he shot the particles in the orbit what direction they would go.

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As the physicist Ernest Rutherford, observed his experiment he saw that many of the particles changed direction, came back at him and others went straight through the foil.

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Some of the particles bounced back because the nucleus was hit in the center and caused it to bounce back.

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Rutherford concluded that the particles changed direction because it contained a small particle, which is now known as the nucleus of an atom and therefore his theory was correct.

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Compounds are formed by a combination of two or more different kinds of atoms.

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Compounds are formed by a combination of two or more different kinds of atoms.

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Molecules form when two or more atoms come together chemically. If atoms that are of two or more different elements combine you get a compound.

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James Chadwick was assigned the task of tracking down evidence of Rutherford's tightly bound "proton-electron pair" or neutron.

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*Cathode ray tube deposited an electric charge. https:aip.org.
*The negative  charge and the cathode rays must  be stuck together: you cannot separate the charge from the rays. https:aip.org./exhibits/electron/jj1897.htm
*When they were bent away the electrometer it did not register much electric charge. https://www.google.com/amp/slideplayer.com/amp/4279834/
*Cathode used the ray tube to discover the electron .https://study.com/academy/lesson/jj-thomsons-cathode-ray-tube-crt-definition-experiment-diagram.html
*The cathode is a vacuum tube  containing one or more electron guns and a fluorescent screen used to view images.https://study.com/academy/lesson/jj-thomsons-cathode-ray-tube-crt-definition-experiment-diagram.html

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Cathode Ray Tubes in Your Home

You might have used a cathode ray tube even if you've never even heard of it until reading this lesson. Before LCD and Plasma TVs became commonplace, most people used bulkier cathode ray tube (CRT) televisions. The CRT in a television is used to display images on your screen. However, cathode ray tubes have been used for more than entertainment. It was cathode ray tubes that allowed the English physicist J.J. Thomson to discover the existence of electrons in 1897.

How Cathode Ray Tubes Work

Before we see how J.J. Thomson used the cathode ray tube to discover the electron, we need to know how a cathode ray tube works. We'll look at a basic CRT like what J.J. Thomson would've used, as seen in the diagram below.

The CRT consists of several elements starting with a tube that's vacuum sealed to keep air out of it. On one side of the inside of the tube there's a cathode and an anode. The cathode is a negatively-charged conductor, and the anode is a positively-charged conductor. Electrons, which have a negative charge, flow off the cathode and are attracted towards the anode. A small hole in the anode allows some electrons to pass through it, creating a beam of electrons. On the opposite side of the tube is a coating that glows when struck by the electrons. This allowed J. J. Thomson to see where the electron beam was hitting.

Of course, before his experiment, we didn't know electrons existed. So, no one was calling it an electron beam. Instead, what flowed off the cathode toward the anode were called 'cathode rays.' Hence the name cathode ray tube.

The Three Experiments

J.J. Thomson's discovery of electrons didn't happen all at once. Instead, it was a result that was slowly built towards over the course of three different experiments. Before Thomson's experiments, it had already been discovered that the cathode rays deposit an electric charge. This was done by putting an electrometer at the opposite end from the cathode and anode. When the cathode rays hit the electrometer, it measured an electric charge.

The first experiment was done in order to see if the charge was separate from the cathode rays. Thomson used a magnet to bend the cathode rays away from the electrometers. When he did this, he discovered that the electrometers stopped measuring electric charge. From this he deduced that the electric charge and the cathode rays must be combined together and not separate entities.

Next, J.J. Thomson set out to determine if the charge carried by the cathode rays was negative or positive. To do this he would use an electric field. He put a negatively charged metal plate on one side of the cathode rays let out past the anode, and a positively charged metal plate on the other side. Instead of an electrometer at one end of the CRT he now had a fluorescent coating that would glow where the cathode ray hit it. When the charged metal plates were introduced he found that the cathode rays bent toward the positive plate and away from the negative plate. This showed that the charge carried by the cathode rays was negative.

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j.j. thomson's cathode ray tube (crt): definition

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experiment & diagram - video & lesson transcript | study.com

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J.J. Thomson's Cathode Ray Tube (CRT): Definition, Experiment & Diagram - Video & Lesson Transcript | Study.com

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You might have used a cathode ray tube even if you've never even heard of it until reading this lesson. Before LCD and Plasma TVs became commonplace, most people used bulkier cathode ray tube (CRT) televisions. The CRT in a television is used to display images on your screen.

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Chadwick found out that Rutherford's "proton-electron" pair was incorrect. There was no "free electrons" in the nucleus but unstable neutrons.

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He showed that cathode rays can cast shadows, then demonstrated how such rays are emitted, perpendicular to the cathode surface, and can be manipulated with magnetic fields.

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Goldstein concluded that in addition to the electrons, or cathode rays, that travel from the negatively charged cathode toward the positively charged anode, there is another ray that travels in the opposite direction, from the anode toward the cathode.

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In the second experiment he was trying to see if the ray carried negative charges

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In the second experiment he was trying to see if the ray carried negative charges

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*Because of past experiments failing he changed the Cathode Ray by adding florescent coating at each end.
*In the middle of the tube were two electric plates making both positive and negative Anodes.
*His hypothesis was correct and negative charges were going to be produced.

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In the beginning the atomizer sprays the mist of oil drops on the top chamber.

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The oil droplets fall through a small hole cut in the top metal plate.

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The space between the metal plates is ionized by radiation and electrons from the air attached them selves to the droplet. The oil drops then acquire a negative charge.

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a chemical reaction is a rearrangement of atoms in the reactant and the product compounds

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he showed that the atom is mostly empty space with a positive charged nucleus in the center.

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A light source illuminates the oil droplets and by the speed at which the droplets fall, their mass is measured. The amount of voltage needed to suspend a droplet is used along with its mass to determine the overall electric charge of the droplet.

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the word "atom" literally means indivisible. atoms are homogenous with no structure inside

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Thomason's 3rd experiment with Cathode Ray Tubes

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Thomason's 3rd experiment with Cathode Ray Tubes

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3rd experiment
*determine the basic properties of the particle
*couldnt really measured the particle but he could measure how much the rays bent from a magnetic field including the energy it carried
*using his data he calculated the ratio of the mass to the electric charge
*used different gases and tubes
*the mass to charge ratio turned out to be far smaller than of a charged hydrogen atom (more than a 1000x's)
*"either the cathode rays carried an enormous charge (as compared w/a charged atom) or else they were amazingly light relative to their charge"

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As you use this method repeatably, the electric charge on oil drops are always whole-numbers.

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With his experiment Rutherford was able to find the size of the nucleus by carefully measuring the fraction of the particles that changed directions through large angles. He found out that the size is 10,000 times smaller than the radius of the atom.

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This method at last shows proof that an electric charge exists in basic natural units.

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http://www.britanica.com/science/Millikan-oil-drop-experiment