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0:00
This is a periodic table. You've probably seen a periodic table before. It shows all the elements that make up our universe. However, this one that you can see I've done a little bit different. My whole goal is to help you out in anatomy and physiology. So I've only put on here the most important elements that will come up when you take anatomy and physiology. So we'll put important elements in A and P. Now I'm going to start with the most common.
0:30
I'm going to color these ones with kind of a red color, and these are going to be the most common, and they make up most of what you weigh. 96 percent of your body weight or mass is from these four elements, and they are, maybe you've learned this before like in a high school biology class, carbon, Hydrogen, that's over here, number one. Oxygen and Nitrogen. So we can use the acronym CHON to remember these. Carbon, Hydrogen, Oxygen, and Nitrogen.
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The numbers that you see above them, so for example, you see a 1 right here, a 6, a 7, and an 8, that tells you the atomic number, which is the same as how many protons that particular element has in its atoms. The next group I'll show you are called the electrolytes, and these are the important ions that float around in our body fluids, both in our blood and in our cells. So I'm going to call them electrolytes. A chemistry person would refer to them as ions, But these are
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ions in your bodily fluids,
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and these are important for all of the electrical activity that goes on in your body. These particular ones that I'm going to show you are also going to make up the salts, the solid salts in your bones and teeth. So these include very familiar substances like sodium. See this number 11? N A stands for sodium, number 12 M G stands for magnesium, 19 is potassium, and 20 is calcium. And in your bodily fluids, all four of these will become cations, which are
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positive ions, and they're either going to be plus one or plus two charge, which makes them not be neutral. They are able to contribute to the membrane potential or the electrical currents that are going to be making your muscles contract. There is one more very important ion, and come over here to number 17. Do you see that CL? That's chlorine, and it will form an ion in your bodily fluids with a charge of negative one. I'm going to talk to you about why those things happen as we go on.
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So those are the electrolytes or the salts. In your bones. You can have calcium salts and those form hydroxyapatite crystals that make your bones and teeth hard and that's in a solid form, but the rest of the time they come apart and they're charged in your bodily fluids. Then the last one I want to tell you about, are the trace elements. And these are elements that really are very rare as far as how much of your body is made up of them, but they are very important, of
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course, in their jobs and you need to have that small amount of them. So the trace elements that I've chosen to highlight here are ferrous, which is just the Latin name for iron, 26, then 29 and 30, copper and zinc. These are both very important in a lot of enzymatic reactions, meaning they help chemical reactions to proceed as planned in your body. Then come down here to number 53. This is iodine and you don't need a lot of iodine, but you
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do need it in order to make your metabolic hormone called thyroxine. Now the fourth group that I want to mention here is not even involved in chemical reactions in your body because these ones are inert or non reactive. But it's helpful for you to know a little bit about them because then you understand why some things like to make chemical bonds and other things don't. These ones over here, helium, all in this column, neon, argon, krypton,
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Xenon and Radon, these are all so stable that they don't react with anything. We call them the noble gases because they do not form bonds. They're so stable they are inert. That means non reactive. They do not form chemical bonds. So any chemical reactions in the body, they're not going to include these. But we talk about them in the beginning of Anatomy and Physiology, so you can see what a stable element looks like, and therefore all the other ones we just
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talked about are not stable on their own. They want to form bonds. Now I'm going to define an element down here. You can just think of an element as a substance that can't be broken down any farther.
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An atom is the smallest unit of matter that still retains the properties of a particular element. So you could have an atom of aluminum, and then you could have billions and billions of atoms of aluminum in aluminum foil. So atoms are the smallest unit of matter that still retains the properties of a particular element. Atomic structure. Now that you've seen a little about how the periodic table is organized, let's look at an individual atom to see what its structure is.
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I'm going to use as our example carbon, because carbon is the backbone atom of all of the big molecules in your body. So that's why we call things carbon chemistry, for example, or organic chemistry because they all use carbon because carbon likes to form four bonds. And so it's like the most versatile Lego you could have. So I'm going to show you the structure of carbon on the periodic table. This is what its box would look like.
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It would have this number six right here, which is its atomic number, which you may recall means also its number of protons. Those two things are synonymous. So if we were going to draw the structure of an atom, we want to give it six protons. Protons have positive charges. So I'm going to draw six protons to represent carbon. That's all you have to know that a particular atom is carbon, is its number of protons. If it had five protons, it would be boron.
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And if it had seven protons, then it would be nitrogen. So the number of protons is what determines the identity. And you're always going to know that a proton is going to have a plus charge. So it is not neutral. It's located in the nucleus, really just like the center of the atom,
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and it has a little bit of weight. We say one atomic mass unit, or AMU, we abbreviate that. All right, so I told you this is carbon with six protons. If it wants to be neutral, then we need to have the same number of electrons. So we're going to put some negative charges around it. And let's go ahead and draw what's called an electron shell. This is the first electron shell. And because it's little, it can only hold two electrons. But if it does have two electrons, it's full and stable.
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So we'll go ahead and put two electrons on here. I'll put one here and one here. And these electrons have negative charges, so I can put that in the middle just to remind you that these are negative. So on the other side of our page we'll write electron is going to have a negative one charge. It's going to be found in, they call it an electron cloud, but I think for A& P if you just remember electron shell that will help you with the questions you're asked.
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and it has what we call a negligible mass, meaning it's so tiny that we don't measure it. So when we figure out how much the mass of an atom is, we don't calculate the electrons. We get to ignore them. I showed you that there are two electrons here and there are six protons, but if that were the case, you would have four more positive charges than negative and it wouldn't be neutral, right? A neutral atom will have the same number of protons as electrons.
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We can go ahead and add those like this to a second shell like this. This is the second electron shell, and it is full and satisfied, I'll put stable, with eight electrons. So it could hold eight, but in order to get to six we only need four more, right? Because we've already got two. So we can do One here, one here, and one here. Remember how I told you that an atom, in order to be neutral, needs to have the same number of protons as electrons, but only the protons have mass?
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So if the mass of a proton is one atomic mass unit, then the mass of this atom would be six, but that's not actually the case. It's actually 12. So this is the atomic mass of carbon. Where are those other six atomic mass units coming from? Well, they're coming from atomic particles called neutrons. I'm just going to use blue circles to draw these, and you can see that if There are six protons and the mass is 12. You must have to have six more atomic mass units, and those come from the neutrons.
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The neutrons don't have a charge, that's how they got their name. So we say no charge, they're neutral. They're also found in the nucleus, and they also have a one atomic mass unit. I'll just use AMU because you know what that is now. Notice that the atomic mass is a decimal. It's a decimal because not all of the atoms have six neutrons. Every once in a while there's one with seven and so you get this weighted average. The average of all of them in the universe is 12. 01
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because some atoms have seven neutrons. But every atom of carbon will always have six protons because that's how we know it's carbon and not a different element like nitrogen. Here I want to show you the atomic structure of Chan, those most important atoms and elements that are in our body that make up 96 percent of our body's mass. So I'm going to do one, six,
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7 and 8. And the 1 represents the atomic number of hydrogen, the 6, carbon, the 7, nitrogen, and the eight oxygen. And this is just going to help you get more confident with the differences between the atomic particles. Hydrogen has one proton. Carbon, as we've looked at already, has six protons. Nitrogen has seven, and oxygen has eight. These plus signs represent the protons. Notice that atomic number matches the number of protons. They're the same thing.
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If you know the number of protons, you know the identity of the element. Okay, the next thing we'll do is start adding the appropriate neutrons, which are also found in the nucleus. So hydrogen will typically have one neutron, and that means that its atomic mass is going to be one proton plus one neutron for two because a proton has a mass of one and so does a neutron. Like that. Now let's look next at the carbon. So carbon has also typically six neutrons.
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So we could put these just around the sides here, but they are part of the nucleus. Carbon's atomic mass is 12, so if we add up six protons plus Six neutrons, we get 12 for the atomic mass of this atom, which makes sense. Now let's try nitrogen. Nitrogen will typically also have the same number of neutrons as protons, doesn't have to.
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We'll talk about later that if the neutron number varies and you have what's called an isotope. There's seven, so we go Seven protons plus seven neutrons, and we come up with a mass of 14 for nitrogen. See how the electrons don't matter to figure out the mass.
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And then last we come to oxygen, and it too will typically have the same number of neutrons as oxygen. for eight. So we can go eight protons plus eight neutrons equals a mass of 16. So the takeaway is that neutrons are critical for knowing the mass of the atom that you're studying. Neutron numbers can vary.
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So you could have a hydrogen, let's say, with two neutrons, and then its atomic mass would be three, or you could even have one with three neutrons, and then its atomic mass would be four. So that's not as common, but that's what we call an isotope, and we'll talk about that on the next page. Last, let's draw the electron shells. Hydrogen, in order to be neutral, only will have one electron, right, to match its one proton. So it only needs one electron shell. Carbon is a little bit bigger atom,
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so its first shell also can only hold two. And it's full like that, but it, in order to be neutral, has four more. We did this on the last page, so it's going to need a second shell like this, and then we can put four more in that outermost shell, and the outer shell is called the valence shell. So see how carbon needed two shells. And the outer shell is always called the valence shell. So carbon has four valence electrons. And notice that hydrogen has one valence electron.
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The valence is just the electrons in the outermost shell. Because those are going to be the ones that help determine electro, er, because those are the ones that will determine chemical bonding. Okay, then nitrogen will need to have two here, but it's got seven protons, so to be neutral it needs seven electrons to balance those out. So we're going to throw on another shell. And we need 5, right? 2 plus 5 is 7. So we can go 1, 2, 3, 4, 5. I just randomly spread those out.
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I'll put the little negatives in here. And then you can see that in its valence electron shell, it has 5. Then we'll do one more. Can you guess how many oxygen we'll have as valence electrons? Once again, we'll just put two in the first shell.
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And then we need another shell. Then as you go down the periodic table, you need three, and then four, and then five. You can get lots of shells, but we don't need to worry about that for AMP. Just want you to get a general, comfortable overview with atomic structure and what atomic mass means. Remember that's when you know, need to know the neutrons. You're going to need to know what an isotope is. So we'll talk about that next. And then these, this one has six valence electrons.
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This is what is going to determine why oxygen, for example, likes to form two bonds, why carbon likes to form four bonds, and why hydrogen likes to form one bond. We'll talk about that, too, in the coming page. Neutrons are the part of an atom that determines whether it's an isotope and which isotope it is. So this page we'll call Neutrons and Isotopes. And I will give you a couple examples here. We're going to look at carbon. We've been looking at carbon a lot.
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You might even remember now that carbon has six protons. I'm going to draw carbon with its six protons and like we did in a previous page, it's typical six neutrons because it usually has six. And you can tell that when you look at its atomic mass on a periodic table and 12. 01, that tells you that sometimes it has more than six neutrons. As a refresher, we'll draw It's two shells for electrons, and it has two electrons in the first shell, which makes that first shell full.
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And then it's got four electrons in the second shell, which means it could hold four more. And that's why carbon likes to form four bonds. So you can see that the atomic mass is going to be the protons plus the neutrons. So six plus six equals 12. So this one is going to have an atomic mass of 12. This is the most common form of carbon,
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but because that average is 12. 01, we know that sometimes it exists with a different number of neutrons. Here I'll put six protons once again, because carbon is always carbon if it has six protons. But this time I'm going to draw eight neutrons. and then I'm going to put the electron shells, the first one, and then the valence shell. And those are going to be the same, right? You're going to have two in there, and then the second shell
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will have four, meaning it could hold four more, and that's why carbon likes to form four bonds. The atomic mass of this carbon atom is bigger. It's going to be 6 for the carbon and then 8 for the neutrons equals 14. So notice that it's still carbon because it has 6 protons. In fact, I could put that in this orange because that's what we've been doing. And then the neutrons we could put in blue just to remind ourselves. This form of carbon is still carbon and it is far less common.
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And so we call these isotopes. Anytime you have a carbon with a different number of neutrons, then they're considered isotopes to one another. We call this one carbon 12 and we call this one carbon 14. And these are isotopes. The reason that I spend a couple minutes talking about this in anatomy and physiology is because it has application to what we call nuclear medicine, where we use radioactivity to treat people. So when you have carbon 14, we call this a radioactive isotope,
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and that just means that it is unstable, and it's going to rapidly degrade and give off radioactivity. Whereas carbon 12, the one we're more used to, is a very stable isotope, and it's not radioactive. In nuclear medicine, we use a variety of different radioactive isotopes for two reasons. So we can use radioactivity to help visualize in order to diagnose, and then we can use radioactivity to kill cells in order to treat cancers.
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We'll use this periodic table here to show how the number of valence electrons of an atom are what determine its chemical bonding.
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That's important in anatomy and physiology as we consider the type of bonds that are formed in the molecules in our body. Phalence electrons, those are the ones in the outermost electron shell, determine the types of bonds that atoms can form with one another to either make molecules or compounds combining these different atoms together. We'll show you how this works. First, let's look at the atoms that are non reactive. Number two, helium. It has a full electron shell with two.
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So it has a full valence shell with two electrons. So it's completely stable like that. And then all of these ones are also completely stable like that. because they all have eight electrons in their outermost shell. The outcome of this is that these are the noble gases. That is a historic way of helping people recognize that they are inert, which means the same as non reactive. They will not form bonds. So if you start with that, that's the perfection, right?
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That these all have full valence shells. Now let's look at the rest of the periodic table so that we see why the other ones will want to form bonds. Closest to the noble gases, we have this column right here, and these have seven valence electrons. So that's going to include chlorine. So chlorine wants one more electron so badly. If it has that one more electron, it will be perfectly happy and stable. It wants it so badly that it will typically steal an electron from another
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atom, something like sodium usually, and in the process it will become an ion with a negative one charge, and a, an ion that has a negative charge is called an anion. Oxygen is the column we'll discuss next. All of the elements in this column have six valence electrons. They have six valence electrons, and so they want two more. So for that reason, oxygen will usually form two bonds to be stable. The next group over has five valence electrons.
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And this column, maybe it doesn't surprise you, but it's a little more variable because it is not quite as close to perfection as something like chlorine. So its behavior might vary depending on which other atoms it's around. So we won't talk too much more about that one because, hey, we're trying to do big picture stuff, right? The column that contains carbon is so important Because carbon is going to be the backbone of all of the big molecules in your body.
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Carbon and others in this column have four valence electrons. So carbon wants four more valence electrons so that it can have the full complement of eight. And for that reason, carbon will typically try to form four bonds with other atoms, especially hydrogen, oxygen, and nitrogen. And that's why it is the star player. When we talk about big molecules like carbohydrates, lipids, nucleic acids, and proteins. Oops. It looks like I forgot to. Fill this column the rest of the way in.
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This column right here includes elements such as boron, and they will typically have three valence electrons, but again, not so important for our discussions in anatomy and physiology. So we'll just leave it like this. The middle elements in the periodic table are more variable and complex in how they interact, and we can happily skip over that for your foundation in anatomy and physiology. But we need to get to the very important next group, which includes what will
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form important electrolytes or cations in your body, such as magnesium and calcium. This column, they all have two valence electrons. And so in order to be stable, they would want six more, right? But it's actually easier to give away two than to gain six more in order to have a full outer shell. So This column they want to give away two
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and maybe you can see where we're going with this then but we'll end with this last group which includes very important cations or ions that are positively charged that include things like sodium and potassium. This column all contain one valence electron. So they're seven away from a full outer shell. So it makes more sense to give away one valence electron and have their outer shell full, than to try and get seven more. So they very badly, want to give away one.
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These two columns are so unstable with their current valence electrons that for the most part what we will see is that they will gladly give away one or two electrons. And they do this to become more stable.
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So essentially they always exist as cations with a plus one charge for this column and a plus two charge for that column. So a cation is a positive ion. Somewhat similarly, Chlorine is so close to having a full shell if it could just get one more, that it essentially always steals or grabs an electron from sodium, potassium, magnesium, or calcium in order to become more stable. And it then exists, as I showed you before, as a negative ion, which is called an anion.
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So we could add that right here, anion. Time to talk about ionic bonding.
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I will use table salt or sodium chloride as our classic example of an ionic bond. Ionic bonds form between metals, those are on the left side of the periodic table, with non metals, so you have to have one of each to pull it off, and those ones are on the right side. And then the ones in the middle are also metals, so most of the periodic table is metals actually, and fewer are non metals. But in order to have an ionic bond, you have to have a metal with a
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non metal, whereas other kinds of bonding you can have two non metals. The other thing that you got to make sure you remember about ionic bonding is it always involves the transfer of electrons.
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And this is important to remember Because other kinds of bonding, covalent bonding, that involves sharing of electrons and you almost always get asked a question like this on an anatomy and physiology intro to chemistry chapter test. Now I'll show you how sodium or Na binds with chlorine or Cl to form an ionic bond. First, we'll put the protons. Sodium has 11 protons, so let's go ahead and put those here. 1 2 3 4 5 6 7 8 9 10 11. When we go to put the electrons on there, we don't care about
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the neutrons at all right now. Since those don't have anything to do with the bonding part, let's fill our first shell with two electrons and then the second shell we can put eight in and then that will be two plus eight gets us to ten and then we have to do one more. So we'll do two, four, six, eight, And then with the two in the middle, that's 10. And then that means that we have to add a third shell. And the third shell is only going to have one electron right here.
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And that's why sodium really wants to donate this. It wants to give it away. And that's why it will exist as a cation. Ion. immediately, like it's so unstable like this that it doesn't exist this way in nature, like with that electron. It will give it up immediately, so you won't find it like this. Makes a big explosion. Donates its one electron, one valence electron. to form sodium, which is a cation or positively charged ion. So we added its 10 electrons, which means, do you see how it has
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one more proton than, electron. So we say that it is a plus one cation. And all of the elements in this column of the periodic table are like this. Now we'll look at the experience of chlorine to see why these two bond together so often and form what's called an ionic bond. Chlorine has
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And we'll do, okay, first shell, 1, 2, 3, 6, 7, 8, 2, 6, 7. Now let's, so those are its protons in the nucleus. Then we'll give it its first electron shell. And Put two electrons here, one, two, then the next shell can hold eight, right? We'll go one, two, three, four, five, six, seven, eight. So now we're at ten, right? Now let's do another one. And , if it has 17 protons and we want it to be electrically neutral, we'll add 7 here. So 1, 2, 3, 4, 5, 6, 7.
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See how it's just missing one in that third shell. The electron from the third shell from an atom like sodium will be donated to a greedy atom like chlorine and chlorine will get an extra one and sodium will lose it because it donates it. So we call this a transfer of electrons. In this case, there was just one that got transferred, right? And now there's an attraction, and the ionic bond forms from the attraction of positives and negative.
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However, they don't actually stay in a solid form in our bodily fluids. In our bodily fluids. this compound will dissociate, that means come apart, back into its ion form. And in this case, it would be sodium and chlorine. Oh, what I also should have put over here is in chlorine will immediately steal So rather than donate, it will immediately steal an extra valence electron to form chlorine minus, which is an anion. That's a negative ion.
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So what up here, top left, this is the solid salt is what we call it, and then when it's dissolved in your bodily fluids, these are the electrolytes in fluid. Ions are important in our body.
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They are responsible for brain activity, all electrical activity in our body. They are responsible for muscle contraction and keeping our heart beating, which is a muscle.
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How do they do all this, you wonder? If you can imagine that This is a cell in your body. Then sodium ions can enter and potassium ions will leave and it's the movement of ions in and out of our cells is how our body controls actions. This is an important key concept.
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There are a couple of occasions where ions can form solid ionic compounds, like salt, in our body. Your bones are made up of a solid ionic compound called calcium phosphate. I'll write that out for you. Calcium phosphate. And calcium phosphate can form larger structures called hydroxyapatite crystals. Hydroxyapatite crystals. And this is what makes your bones hard. They're mineralized. Your teeth are also made of hydroxyapatite crystals. At least the enamel on them is.
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It's the hardest structure in your body. Pure hydroxyapatite crystals, basically. So I'll go ahead and color this mouth, lips right here, and then let's put a label on here that teeth are also made of hydroxyapatite crystals, or the enamel that protects them. Another role of ions in our body is that ions form acids and bases. Some important examples that you'll learn about in anatomy and physiology. One, hydrochloric acid. This is produced by our stomach.
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And it helps to begin the digestion process and also to destroy pathogens or things that could make you sick.
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In our blood, the production of carbon dioxide by our cells produces a weaker acid called carbonic acid. And it's in our blood, and it comes from the carbon dioxide that's generated by our cells.
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And that then could make our blood acidic, and so we need to breathe off carbon dioxide in order to get some of that acid out of our body. Then there's lactic acid. It's got a big formula, so I won't write it all out for you here. But lactic acid is formed also by our cells when they're oxygen starved and you're exercising. So that's when you feel the burn. And that can also lower the pH of your blood. And then one last acid that you'll hear about in anatomy and physiology, uric acid.
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And this one is formed by our liver as part of its normal processes.
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covalent bonding occurs between two non metals. Remember, those are the elements mostly on the right side of the periodic table, although hydrogen is in lots of covalent bonds and it is on the left side. That's an exception. And rather than a transfer, of electrons. It is a sharing of electrons. So when we talked about sodium chloride, what happens is that chlorine completely takes an electron that used to be going around sodium, and now that electron is going around chlorine.
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So that's why we call it a transfer. But in a covalent bond, you have a sharing of the electrons, so the electrons are going to continue to go around both of the atoms instead of being hogged by one entirely. Let's draw a carbon. This is going to have six protons. And then that means that it's going to have two shells, right? Because if it has two electrons in its first shell and then it needs four in the next shell, right? I'm going to make the valence electrons black for this carbon.
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One two three four. for valence electrons for carbon. So it wants to have eight right now. It can interact with a hydrogen here and here. And watch what happens when hydrogen interacts. I'll use blue for its valence electron. So look, Here's one. Here's one. And so these are shared pairs of electrons. See the sharing right here? There's this nice equal sharing. So now hydrogen has two valence electrons. And remember that first shell is full with two.
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And so that means that hydrogen is stable and happy. And then when this is over, now, if we count them up, we can see that carbon has 1, 2, 3, 4, 5, 6, 7, 8 electrons. So now carbon has eight valence electrons, which is full for that second shell. So it is also stable. So they form a molecule called methane. And it's a compound because it has carbons and hydrogen. So it has more than one kind of atom. And this methane is going to be made up of these single bonds. So this is a single bond
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formed by shared electrons. And that is what a covalent bond is. Now, these are also nonpolar bonds because that sharing is equal. If, for example, the carbon were to keep the electron around it more of the time than the hydrogen got to have the electron around it, then it would be an unequal sharing, and we will talk about that later. Now I want to show you how a double bond could form. We'll start with carbon again. We'll put it right here.
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There's a carbon, and here is its first shell with those two valence electrons, and then it has to have a second shell, right? What it can do here is instead of sharing one pair with each atom the way it does with hydrogen is that it can share two with just two other atoms so instead of bonding with four hydrogens it could bond with two oxygen so i'm going to put o over here for oxygen and oxygen has eight protons. I'm going to put that here like this.
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So it's valence shell will have six electrons. But we'll do the first shell like this. Now watch carefully for this next one. We'll go vroom. And vroom. See how they're going to share? And I'll use blue again. So it's going to share. See that? How they're sharing? It's almost like they're linking arms. So each shared pair of electrons is a bond. So there's one, and there's one. So this is double bond right here. Double bond because you've got two shared pairs.
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And then here's another one right here. Do you see? There is, for this one, the double bond between this carbon and oxygen. And then another one right there.
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So these are double bonds. And this is also non polar. Because the electrons are going to be spending the same amount of time around the oxygen as they are around the carbon. So it's being pulled equally and shared equally. Now oxygen has six valence electrons, and we've only accounted for two when it bonds with the carbon. So the other ones are what we call lone pairs. They hang out over here. So you've got two, four, six. Now you've accounted for all six. And then the same over here.
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And those electrons, are pulling toward the oxygen but since you have an oxygen on either side they balance each other out and it's still what we call a non polar bond. Now why do we care about non polar covalent bonds in the body?
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The main examples of non polar covalent bonds in your body are going to be lipids and gases. So the one that I just drew for you on the previous page was carbon dioxide. So there was that central carbon and then we use symbols like this to show double bonds. So see how there's two lines. Each line represents a bond. So you've got two double bonds right here. So we've got a double bond. And this is considered non polar because the electrons are equally shared by all three atoms in the compound.
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Oxygen is also like this in your body. It shares a double bond like this. And we write it like this, oxygen. So these are the main gases in our body. We breathe in oxygen, and we breathe out carbon dioxide. And you might remember I also mentioned to you that carbon dioxide can form acid in our blood, in the form of carbonic acid. Okay, then we'll look at a lipid, which is like a fatty acid, a lipid. So if you eat fat, it's these long carbon chains. Do you see this long carbon chains?
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And these are all made up of covalent bonds. And then remember I told you how carbon likes to form four bonds. So here at the end you would have these hydrogens. Remember I told you that Carbon likes to form four bonds. So if this right here is a single bond, then it wants four, three more, right? So it can just bond with three hydrogens like this. Do you see that? And then this carbon right here needs two more to get four. So then it's got one, two, three, four, right?
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And then this one is the same. See how they get all these hydrogens? If they Have as many hydrogens as possible. We say that it's a saturated fat because it couldn't have any more hydrogens. But sometimes you can have a double bond, watch this. I could put another bond. Let's just even put one right here. Okay. So now we've got a double bond right here. So now this carbon has one, two, three, four, five. That's too many, right?
58:33
So we'll take off one of these hydrogens so that it still only has four bonds. And then this one, this carbon right here, one, two, three, four, five. It also has too many hydrogens now. So we would take off one like that. So then this would be a double bond. You can also have a triple bond between a gas like nitrogen. Nitrogen is another gas. And you, with that one, it forms three bonds. Look at that. So this is a triple bond. These are all examples of nonpolar covalent bonds in your body.
59:19
Polar covalent bonds share electrons, but their defining characteristic is that they have an unequal sharing of electrons. Water is the most basic polar molecule. I'm going to draw it for you. So here is an oxygen with its eight protons. So one, two, three, four, five, six, seven, eight. So it has six electrons in its valence shell. So this is its basic shell, and we know that's full with two. And then its second shell, its valence shell, is going to have eight.
1:00:24
And I'll use blue like I did on the previous page. So some of these are gonna end up being unpaired like this. So we'll put them over here. See these four? But remember it has six all together, and so it's gonna share one of those with a hydrogen here, and one with a hydrogen here. I'll put the hydrogen right here and right here. And you see how hydrogen's one shell, its only shell, is going to share here and here. Recall that this is a single bond. And this is a single bond.
1:01:13
And then you've got these electrons here and here. These are unpaired electrons
1:01:28
that spend all their time around oxygen. So do you see how that makes that end of the molecule a little bit more negative? So the electrons are pulled toward that end of the molecule.
1:02:11
So we call this a dipole and we draw it like this. Put a negative right here and a positive like that. I know that's funny looking. This is called a dipole. Oxygen is a highly electronegative atom.
1:02:45
Molecules often makes them polar. And when I use this word polar, I mean that the electrons are pulling more toward one end than the other. So do you see how that's unequal sharing?
1:03:27
Polar molecules are important in our body for several reasons. And why we need to know about them as we're laying our foundation for anatomy and physiology. The first is that polar molecules dissolve in the polar molecule water. Water, as we've talked about, is polar, and so it can surround molecules like glucose that are polar. Another word for polar in the biology world, we say hydrophilic. This means that they are water loving.
1:04:10
Something like Glucose or sugar is going to dissolve in water, right? You can make Kool Aid, for example. But something like oil or fat is non polar, meaning it's hydrophobic. Hydrophobic substances do not mix well with water. Now, let me show you something pretty cool. I'm going to draw a few water molecules for you. Here is one. Remember, these lines are single bonds. and that there is a slightly positive end on the hydrogen end and a slightly negative end on the oxygen.
1:04:45
Let's make another one right here, another water molecule that's two hydrogens. There it is, H2O, and remember this is the slightly negative end and then a slightly positive end like that. And let's just do one more for fun. So here's one more water molecule. And it's got that slightly negative end and a slightly positive end. So do you see what's happened here? These are going to be attracted to each other. Look at this. I'll use these purple dots to show where the positives are attracted
1:05:25
to the negatives like this. This is going to help these molecules stay close to each other. We call these hydrogen bonds. So hydrogen bonds, maybe I'll put the word hydrogen. Hydrogen bonds are weak but adequate for helping polar molecules cling together. And they form in the human body between oxygens and hydrogens, and between nitrogens and hydrogens because nitrogen is also electronegative like oxygen, Water's special properties are mostly due to these hydrogen bonds.
1:06:34
These are responsible for characteristics of water that are important in understanding how our body works. So I'll try to give you a few examples of this. First of all, water will have a high surface tension. That is when the molecules want to cling together.
1:07:02
naturally have a little bit of water on them, and we have to reduce surface tension premature babies can struggle with this and that's why they might have trouble breathing. I'll put biological significance, lungs, and surface tension in premature babies. Hydrogen bonds make water have a high heat capacity. Hydrogen bonds may be weak, but there are a lot of them, and they have to be broken before water can evaporate or change temperature.
1:08:27
and or evaporates. So it's going to help keep your body from changing temperature when it's different temperatures outside your body and it also helps to carry away heat from your body when you're sweating as it evaporates. The hydrogen bonds of water and water cause it to have a higher density than most liquids.
1:08:57
And that's because, as I mentioned, those hydrogen bonds help hold the water together. What this ends up doing is it makes water a good cushion because it's a little bit denser. So water can be a good cushion, and I'd like to give you two examples. One is amniotic fluid. That cushions a little baby, and also cerebral spinal fluid or that cushions your brain.
1:09:43
covalent molecules in our body.
1:09:56
Remember that word polar also means hydrophilic in a biological context and it means something can dissolve in water. So that's the first thing I want to show you. Carbohydrates are polar and that means sugar which is a carbohydrate is polar. And so they can dissolve in water because water is a polar molecule and it's the universal solvent. It can dissolve more things than anything else in the world. Carbohydrates are polar and can dissolve in water. We draw glucose like this.
1:10:36
It's like a ring shaped structure. And so we can have glucose dissolved in our blood. And that's how we measure blood sugar. Water, indeed, is the universal solvent. It can dissolve so many things. It can also dissolve proteins, which are polar molecules. I'm going to draw you a little protein right here. Each of these red circles represents an amino acid. And these are the building blocks of big biological molecules called proteins. They're connected with covalent bonds, right?
1:11:26
That's these lines. We've learned about these. These are the bonds that would connect the amino acids. But you see how I made it curved? And that's because Hydrogen bonds can form within the molecule between different polar areas. So like between an oxygen and a hydrogen or between a nitrogen and a hydrogen. So the hydrogen bonds actually help to form the structure of proteins. A protein only works right if it has the right shape which is essential for their function.
1:12:21
They don't work right otherwise.
1:12:33
So dissolving, protein shape, and then the last one I want to do is DNA structure. So DNA is the genetic material in your cells and the structure of DNA is formed into two sides because of hydrogen bonds. So let's say that this is one side of a DNA molecule or one strand. . DNA is what we call a double helix. It has another strand that is like this, so there's the other strand and it's hydrogen bonds that form between oxygens and hydrogens, or between nitrogens
1:13:20
and hydrogens within the molecule that help it hold the two sides together. So see all these hydrogen bonds hold the two sides of DNA together.
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