what is the most significant conclusion that thomson was able to draw from his measurements? This is a topic that many people are looking for. bluevelvetrestaurant.com is a channel providing useful information about learning, life, digital marketing and online courses …. it will help you have an overview and solid multi-faceted knowledge . Today, bluevelvetrestaurant.com would like to introduce to you Discovery of the Electron: Cathode Ray Tube Experiment. Following along are instructions in the video below:
This video. Were going to talk about how jj thompson discovered the electron in in 1897 using the cathode ray tube experiment so these days. We think about atoms of like this theyre made up of a variety of smaller subatomic particles.
But in the late 1800s. It was all about john daltons model of the atom in the early 1800s. John dalton.
Had proposed that all matter all stuff was made up of tiny indivisible particles called atoms at first not many people believed him. But throughout the course of the eighteen. Hundreds more and more scientists got on board with his idea.
But it remained an open question. Whether the atoms were really indivisible were they like tiny little billiard balls. You know hard and solid or were they made of smaller things.
No one really knew the answer that but jj thompson was able to answer part of that question when he discovered the electron he discovered that it was much smaller than atoms. He discovered that adams had electrons and so he was able to say for the first time that atoms werent totally solid and indivisible. But they were made up of smaller subatomic particles lets look at how he discovered the electron.
So thompson used whats called a cathode ray tube. Its a big tube of glass. Thats kind of like a bottle you can imagine.
Its sort of like this soda bottle. Its sealed all over and then you pump all the air out of it okay. And it has these two pieces of metal at this end.
So thompson connected these two pieces of metal to a power source and heres what happened our ray shot from this piece of metal across the tube and created a glowing spot over here when it hit a special coating on the inside of the glass. Now thompson. Didnt know what was going on.
But really was going on is that electrons from this piece of metal. Were shooting out they were attracted to this piece of metal. Which has an opposite charge.
But they were moving so fast. They shot all the way across the length of the tube. Anyway.
Thompson sees this ray and he gets curious as to what its made of and so he asks the question the stuff that the cathode ray is made of does it have a electrical charge and heres how he attempts to answer that question he takes two metal plates and puts them on either side of the cathode ray tube and then he turns on electricity. Which makes the top plate positively charged and the bottom plate negatively charged and check out what happens to the cathode ray. When he turns on the power.
He see that he sees it now instead of going straight through the cathode ray bends up it bends up towards the positively charged plate so based on this he reasons. That the cathode ray must be made of stuff. Thats negatively charged since its attracted to the positively charged piece of metal and he knows that opposite charges attract.
But just because he wants to be very careful. Hes a very careful guy he tries to check this another way so he uses a magnet. If something has an electrical charge and its moving a magnet will push it in particular directions.
So he takes a cathode ray tube. If you want to think that this marker is kind of a cathode ray tube and he surrounds it with a magnet. Just like this we can kind of show what goes on by slipping the magnet under like this so anyway.
He puts the magnet here and he sees now that the cathode ray bends in the other direction. It now moves downward now if the cathode ray is indeed negatively charged. This is exactly how he would expect it to move in the presence of a magnet like this so.
This is just further confirmation that whatever makes up the cathode ray probably is negatively charged. So he takes the the data that he gets from these experiments.
And hes able to draw a few important conclusions about cathode rays and what makes up atoms okay. So based on the outcomes of the experiments with the charge plates and the magnet thompson is able to conclude that cathode rays must be made of stuff that is negatively charged okay he combines the information that he got from the experiments that i just told you about with some other data that he collected and hes able to come to the conclusion that the particles that make up cathode rays are a thousand times smaller than a hydrogen atom hydrogen atoms are the smallest atoms so this thing thats in the cathode rays must be really really tiny compared to an atom and finally thompson swaps out the type of metal thats in the cathode tube. He uses a variety of different types of metal.
But he finds that all of the different metals he use he uses give off the same cathode rays and regardless of what metal. He uses via the size of the things that are in the cathode. Rays is exactly the same so based on these three conclusions.
Hes able to come up with the idea that atoms have tiny negatively charged particles inside them and these things that were talking about here are electrons now if youre like me. When i first learn this you might be confused. How these conclusions definitely tell him that there are electrons inside atoms.
I remember when i first learned this stuff. I was thinking like wait doesnt this just show electricity or cathode rays have negatively charged stuff. How does this tell us anything about the atoms.
Okay. Heres why at the time. That thompson.
Does his experiment. Everyone for the most part agrees that all things are made up of atoms that atoms are the smallest things that make everything up there like the smallest things in the universe. So if thompson is able to show that there are even tinier things well where are those tiny things coming from they have to be coming from atoms.
Because everythings made of atoms right. Thats the only place they can be coming from and even if electricity. Even if you want to say that you know oh well.
Hes just showing that electricity is made of electrons well then still where are the electrons coming from that make the electricity. The electrons have to be coming from other atoms and since he can move and remove these pieces of metal and swap. Other metals in and he still gets electrons it again shows that all different types of atoms are able to release or give off electrons so they must be in there to begin with anyway.
These conclusions that thompson comes to have dramatic effects on how scientists think about what the atom actually looks like now at the beginning of the video. We said that in daltons atomic model atoms are indivisible that theyre not made of anything smaller. But when thompson discovered that atoms have tiny negatively charged electrons inside them.
He essentially disproved this model at least the part about the indivisible atoms. So here is the model of the atom that thompson comes up with he realizes first of all that electrons are negative. We already talked about that but then he notices that on the whole atoms in general are usually electrically neutral.
So even though they have these negatively charged electrons inside them the atoms. As a whole dont have a charge. So thompson realizes that in order for the atoms not to have a charge.
There must be some positive charge in the atom that can balance out the negative charge of the electrons and then the positive and the negative balance out and the atom that as a whole doesnt have a charge. So he comes up with a model that he calls the plum pudding at it now plum pudding is kind of a british thing so if youre american. It might be better for you to think about this as like the blueberry muffin model.
And heres how it works thompson imagines that the atom is like a blueberry muffin and that electrons are stuck in this atom. The way blueberries are stuck in a blueberry muffin. So you have these little electrons that are stuck in the atom.
But then theyre surrounded sort of by a dough and the dough like in a blueberry muffin um keeps these electrons or blueberries held in place but the dough itself has a positive charge and its that positively charged dough that is what balances out the negative charge of the electrons and so together. They dont have any total net charge. So the atom is electrically neutral.
So thats how jj thompsons discovery of the electrons leads to this plum pudding model yeah. But now jj thompson didnt have it quite right because it turns out that the positive charge in the atom isnt he isnt sort of spread out in this dough or pudding. But instead.
Its concentrated right in the center of the atom where the nucleus is so thats gonna be the next step in discovering what the atom really looks like if youre interested in how scientists disproved jj thompsons plum pudding model check out rutherfords gold foil experiment where he discovers that atoms have a very small very dense positively charged nucleus. .
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