00:00:01 TEACHER: Hi, and welcome to today's lesson in physical science. My name is Mr. [? Provancha ?] and I will be your instructor. Today's lesson is in a new unit called atomic structure. And there's three main objectives that we're going to be touching on today. First of all, we're going to talk about the theories behind 00:00:17 the atom and how it's changed over time, from way back to the Greeks to our modern idea of what the model is all about. Next, we're going to talk about the parts that make up an atom. And we're going to talk about their charges, their masses, and where do we find them within the atom. And going along with the whole evolution of the atom in terms 00:00:39 of its model, we're going to, at the very end, talk about a man named Niels Bohr and his model, and how it compares to today's model as well. So we're going to talk about the whole progression of the atom from the Greek till today, and we'll also talk about what we know the pieces of the atom to be now. Now, what are atoms? The term "atom," this means unable to divide. 00:01:03 It means you can't divide it anymore. And the Greeks basically came up with an idea that if you take some sort of material, whether it's a piece of wood or a piece of iron-- whatever it is, if you can keep tearing it apart and breaking it apart and breaking it into pieces, and keep getting it smaller and smaller and smaller, eventually, you're going to get to some pieces that 00:01:25 you can't break anymore. And those pieces they called atoms. Now, they're the first ones to come up with it. A man by the name of Democritus was actually the one who coined this phrase and who really pushed this idea. However, the Greeks-- well, as things do, things change, but they didn't change for a long time. 00:01:45 It was believed all the way up till John Dalton's time, which was 1808-- so this was believed way before BC till 1808 AD. So there's a huge gap in there where people just believed that all matter was just made up of tiny little particles. They didn't really know what these particles were, other than that eventually, you couldn't break them apart anymore. 00:02:05 Now, Dalton comes along and he gives a little bit more into this idea. He still believes that atoms are the smallest piece. However, he now stars recognizing there's different types of atoms. And he starts saying that all gold atoms are exactly the same. All iron atoms are the same as all other iron atoms. 00:02:27 But the gold and iron would be different from each other. So he's the first one to really come out and say that atoms of different elements are different, but atoms of the same element are all the same. So all oxygen atoms would be the same. And that was a new concept. That was something that no one had really come up with before. 00:02:43 And another concept that he started coming up with is that atoms actually could combine with each other to form compounds. And so-- like water had a hydrogen and oxygen. Together, they formed water. And he was one of the first ones to really come up with that idea that water wasn't its own kind of atom. 00:03:02 It was actually a combination of two different types of atoms. So Dalton really kind of broke out of the box and started having some new ideas, and allowed scientists to start researching and start looking into the worlds of atoms a little bit more. So Dalton basically said atoms are the building blocks of everything. 00:03:22 They're the building blocks of molecules. And different parts of the universe are made up of different combinations of these atoms. And that was something, like I said-- was new. Now, so what is an atom? Today we know that atoms are-- actually, they can be divided into other pieces. There's three main parts to an atom that you need to be 00:03:43 familiar with. The first one is a proton. The second is a neutron. And the third is an electron. Let's first talk about a proton. A proton has a positive charge. And it's found in the nucleus. You can see it right in here. 00:04:00 It's in the nucleus. Let's say the red ones are our protons. So we have a positive-- those would all have positive charges. It's a positive electrical charge. And the neutron is very similar to that. A neutron is-- actually, that word "neut" right there means neutral. 00:04:17 So a neutron is neutral. And it's also found in the nucleus. So maybe we'll take these and make these neutrons in there. So the nucleus, as you can see there, is made up of protons and neutrons together. And protons and neutrons, their mass is about the same. We actually give them a mass of 1 amu. That's one atomic mass unit. 00:04:45 That's something that we need to make sure you remember, that protons and neutrons both have the same mass, 1 amu. They're both found in the nucleus, which is in the very center of the atom. The third piece that you need to be familiar with is electrons. Electrons are much, much smaller than a proton or a neutron. 00:05:07 They're very small. And they run around on the outside. The nucleus is in here and the electrons are going around the outside of the atom. And they have a negative charge. So we have a positive for protons, a neutral for neutrons, and a negative for electrons. And it's these charges that really will help us understand 00:05:30 more about how atoms combine to make compounds. That gives us a better understanding of what's going on. Now, if you just have a regular atom, you're going to have no overall charge, which means that all the positives in a proton and all the negatives of electrons, they cancel each other out. And so you'd have the same amount of 00:05:52 positives as you do negatives. And so over all, you have what's called a neutral atom. Even though a proton's bigger than an electron, the charge on a proton is exactly the same amount as a charge on an electron. So you could say those little teeny electrons carry a big punch, but then they carry the same amount of charge as their bigger protons that are in the atom. 00:06:13 So one proton will balance out one electron. Two electrons will balance out two protons. And vice versa. So on a normal atom, you always have the same number of electrons as you do protons. And they balance each other out so that there's no charge overall. Now, along came a man named Niels Bohr, and unlike Dalton, 00:06:34 he believed, and he started proving, that the atom is made up of different pieces. Dalton said it's just one little ball, you can't divide anymore. Bohr, he starts putting the nucleus in the center with those protons and neutrons that we're talking about, and then he starts putting the electrons around the outside, out here, similar to planets going around 00:06:55 in the solar system. And he said that-- well, let me go back here just one second-- he said that these electrons have very specific energy levels, and based on how much energy these electrons have, determines where we're going to find these electrons. Now, comparing Bohr's model to the modern theory, the modern theory doesn't really have-- the electrons don't go around 00:07:21 in these nice orbits like Bohr had it. They act more like waves. And by acting like waves, it makes it impossible to know exactly where those molecules will be. These are pictures of some fans you might have in your room that are just spinning really fast. If you ever look into a fan, you know that there are some blades there. 00:07:40 Because it was stopped, you see three blades. They're just in one position. But if you turn it on, those three blades turn into a blur. And you know that those blades are somewhere in that fan. You know they're somewhere in here, but you don't know exactly where it is at any given time. The same way with the modern theory on atoms is that the electrons-- 00:07:59 we don't know exactly where they are. We know an area. We kind of know the idea of where they might be, but we don't know exactly where they are. And so it's a little bit different that way. As the electrons move around, we know the vicinity, but we don't know their exact location. So that's something new in the modern theory. 00:08:18 Now, going back to those energy levels again, the nucleus is in the middle. This is a combination of the Bohr's and then modern. But there's different energy levels. And electrons exist in these energy levels. They're very specific energy levels. And I'm going to draw them similar to how Bohr would have them, but just imagine that they're kind of like waves. 00:08:39 They're kind of just going all over the place. This would be the first energy level here. And there's only room for two electrons in the first-- in the first energy level, there's two electrons. In the second energy level, there's room for eight electrons. So there can be eight electrons around here. And in the third, we can actually have eighteen going 00:09:03 around here. I'm not going to do all 18. But so each energy level, as you get further and further away from the nucleus, those energy levels can hold more and more electrons in there. And as electrons, they can actually move back and forth between energy levels. They can't be anywhere in between, but if they gain some 00:09:20 energy, they can jump to another level. And based on how much energy they have determines exactly where they're going to be. Now these electrons, like we're talking about these energy levels, where we find them, we actually call it something called an orbital. Not an orbit like the planets, like Bohr-- he said they were going around in orbits. 00:09:44 The modern theory has it called an orbital. And an orbital, as you can see right here, it looks almost like a little cloud. And it's like an envelope where that electron can occur. It's kind of like its boundaries. And you can see they're shaped different ways. This one almost looks like a little balloon this way. Kind of a balloon. 00:10:01 And this one down here looks like a whole bunch of balloons put together. So these orbitals, they have shapes to them. And like I said, the electron-- we don't know where it is, we just know it's somewhere in there. And based on how much energy these electrons have determines the shape of these orbitals. Now, one last thing about electrons that we need to be 00:10:18 familiar with is a term called a "valence electron." And really all this comes out to be is outside-- outside electrons. If we go back to Bohr's model back here, we're talking about valence electrons. We're really just talking about the electrons in that outer energy level. So we can see how we have one, two, three valence electrons 00:10:42 on this atom. All these in here don't count as valence electrons. So as a general rule, there's only between one and eight valence electrons in any atom. And as you get a better understanding of the periodic table, you'll understand why there is one or eight with atoms that we work with. And these valence electrons, why they're significant is 00:11:08 that the valence electrons are really responsible for all reactions that occur. All combinations, all molecules that occur, occur because of the valence electrons. And really, that's about everything we need to know about the atom, is the progression from just knowing that there is an atom to having these energy levels with the orbitals. 00:11:28 Today, we believe those orbitals, versus what the Greeks had before. And so let's go through the objectives one more time to see how we did. First of all, we talked about Dalton. Remember, he's the first one who came up with multiple types of atoms, and how each atom is unique to itself for that specific element. 00:11:44 And that atoms could actually combine to each other. So that was something new. We talked about the charge on a proton, neutron, electron-- remember, proton's positive, electron's negative, and neutrons are neutral. And remember, what's in the nucleus, that's the protons and the neutrons are in the nucleus and the electrons are going around the outside. 00:12:05 And then the difference between Bohr's model and the modern model is Bohr had the electrons going around in specific orbits. They had their energy levels, but he just had them going around in circles. And the modern atom has them in orbitals. And they're going around like a wave. And we're not sure exactly where they are, but we know 00:12:21 they're somewhere in that envelope, somewhere in that-- sometimes called an electron cloud, where we're going to find it in there somewhere, we're just not exactly sure where. So this is all the information that we had today on atoms. Hope this helps you out. Have a great day. Lab Lecture Section 1 00:00:00 TEACHER: Hi. Today we'll be talking about atomic structure and looking at the Bohr model in order to help us compare and contrast Bohr's model with the modern model of the atom. We will be using a Gizmo in order to help us out today. What we get to look at today in this Gizmo is how when we fire a photon of light, what special photons will be detected both in the visible spectrum of light, the colors 00:00:32 that we see red, orange, yellow, green, or in this situation red, green, and blue, as well as in the ultraviolet and in the infrared spectrum. So what we're going to be doing is adjusting the energy bar. Notice that on this bar you can go from 1 electron volt up to 20. So first we're going to have it set at 1. 00:00:56 And we're going to click Fire to fire the photon out. So we're going to shoot this laser beam photon through this gas tube. So we have Gas A, B, and C. So we have this tube here. And we have a special gas in it. So we fire it. What we see is that the red is detected. Now we can't really see the red. 00:01:22 It's infrared. So what is shown is that that is one of the photons that is detected for this gas. We can go ahead and go up to 2. And this would be in the energy level or the correct wavelength for red light. So let's fire it and see if it's detected. And you can see that it is detected. 00:01:44 Every element has its own absorption pattern. It also has its own emission spectrum. So every element is different in their overall pattern, which ones it detects and doesn't. We can click on Lamp to see what Gas A's spectrum looks like. If we fire this, you can see which ones are seen. So you can see that you can see red and 00:02:11 green but not blue. And then you can see several others that aren't exactly colors but are simply energies and different wavelengths. So if we click on Gas B, we could also fire this and see that it is different. It is detecting the blue, whereas Gas A was not. How does this go into Bohr's model? Well, Bohr detected that electrons were able to only 00:02:43 travel in their orbitals, or in their special energy levels. So let's go ahead and look at orbitals. I'm going to go ahead and click on Laser and go over to Orbitals. So there are rings, or orbitals that the electrons are able to travel in. And in order to go from one energy level to another, from 00:03:05 Level 1 to Level 2, it takes an amount of energy or a certain amount of electron volts. This emission of energy is what causes different colors of light or changes in light. So each one of those occurs at a different wavelength, for instance, red, green, or blue. What we have to do to see if this emission happens is see what the energy level is from 1 to 2, or to see what the 00:03:37 change is in the value. So what we can do is see what the value is here. In between 16 and 20 would be negative 18. One more would be negative 19. And right here in between 12 and 16 would be 14, so that would be negative 14. What is the difference that it takes to go from 19 to 14? Well, that would be 5 electron volts. 00:04:06 So we need to change this value to 5 in order to get the emitted photon up to the next energy level. So let's go ahead and move this up to 5 and see what happens. And we'll watch the orbital as well. So we're going to fire this. And notice that it was able to go to the next energy level, because it had a 5 electron volt energy.
