Lecture 07. Ions and Molecules
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Lecture/Conference
Transcript: English(auto-generated)
00:07
Alright, friends. Today we're going to be talking about this, i is a molecule.
00:29
To summarize, we talked in the first week about units and numbers, then we worked with that on Monday
00:40
and then we introduced atoms, and today we're going to talk about that a little more, and then segue into ions and molecules. And it's a very important lecture because it's basically the basics of a molecule. Okay. So here's your table,
01:02
your favorite chart from now on. We'll see actually in a couple lectures this week why this structure takes away this here, but for now, this gets slowly used to some of the elements on there and it's not the purpose of this course to make you try this thing, you know, by heart.
01:25
You don't have to know this by heart. So you don't have to know what all these things are. It's really not the purpose. The purpose is just to understand the systematics. Okay. So let's look at this first guy here. This is by the nucleation of the node. It has one proton and a funnel electron.
01:46
Okay, so it's neutral. Right? It has no neutron. Actually, it has no neutron. Its nucleus is just a proton. The next element, which is like all the way there, on the other side of the table, has
02:01
two protons, but it also has two neutrons. So it is significantly heavier than hydrogen. Hydrogen has only one proton for its nucleus. Helium has four. Two protons and two neutrons. It has charged two plus the nucleus, the single proton has charged one plus. To
02:23
make this neutral, you need two electrons. So the whole atom of helium has these ingredients. Two protons, two neutrons, and two electrons. The next element is right there, number three. Three means three protons. Okay? So it has three protons, it also has neutrons in this case.
02:40
Four. You see the number of neutrons doesn't really follow systematically. This one doesn't have six or something like that. It has four. But it does have three electrons because the number of electrons must be the same as the number of protons for a neutral atom. So knowing this, we can do a couple of very quick exercises that actually will also be repeated on the homework. Which is due tonight at 11 o'clock.
03:11
So how many protons, neutrons, and electrons do the following atoms have? This guy this 17 here means the sum of these protons and neutrons. I just heard it from the
03:25
homework was maybe reversed, I'll check into that but here, the upper value here means the sum of the protons and neutrons and the question here is how many protons, neutrons, and electrons does this atom have? Well, this oxygen, and oxygen
03:41
is number eight on the periodic table, which means it has eight protons. This is the sum of the neutrons and protons, which means if you subtract eight from this, you get the number of neutrons, which is nine. and then the number of electrons since this thing is neutral must be the same as the number of protons. Which is eight. Eight electrons.
04:08
Okay. Let's do another one. Does it work the same for all atoms? Of course, yes. Here's potassium, 39 this is the sum of neutrons and protons potassium is number 19 on the periodic table. That means 19 protons. The number of neutrons you get by taking that sum and subtracting the number of protons.
04:29
20 neutrons. And again, the number of electrons is the same as the number of protons, which is 19. One more. It's not chlorine. Let's not exclude chlorine. Here it is, 37.
04:50
The number on the periodic table is 17 that means if you subtract 17 from 37, you get a total of 20 neutrons. The same amount as potassium, 39.
05:01
That's completely excellent. There's no correlation there. Another number of electrons is the same as the number of protons. Once again, 17. 17 electrons. Very well. This is something I think we can do.
05:21
Is the atom always neutral? No. Very good. It's not. Because I can make ions out of that. What is an ion? Well, ions come in two flavors, it's positive, and negative ions. Okay? So let's look at the positive guys first.
05:42
Here is Mr. X doesn't matter which one it is, it is just the atom and what I do is I pluck away an electron. I just take one out. How I do that is irrelevant. Let's say I can just do that and take one electron out. What I'm left with is something that is positive. Because I'm taking a negative charge. So I'm left with an
06:03
atom now which is positively charged, we call this a cation. We call this a cation. vice versa, what I can do, I can add an electron to it. So here's a neutral atom, I add an electron, consequently, now the whole thing becomes negatively charged
06:24
So this is a monovalent cation, monovalent anion. It doesn't mean that I cannot take two or three. In some cases I can do that. So I can have ions that have charges larger than one. So I can have, in other words, an atom
06:41
with a charge. 3-4t+. Okay, so let's look at some examples. Here's one. Sodium, this is the elemental atom, so to speak. Sodium in its neutral state, but if I take out an electron, I get the sodium ion. There it is. Sodium plus. Same with potassium. Potassium ion is potassium plus. Calcium.
07:07
Actually, it likes to exist as calcium 2+. Let's see why that is later on. At this point you just have to take it for granted. So calcium really doesn't exist as calcium plus. It exists as calcium 2+.
07:26
The same holds for barium. Barium likes to be a 2-plus ion. We call it the barium ion. Chlorine likes to be negatively charged if it is an ion. In its neutral form, it is, of course, neutral. But if it becomes an ion, then it likes to
07:44
be a negative ion. And again, the reason for that, we'll see, will fall into place in subsequent lectures. Iodine, also negatively charged one charge one minus it's called the iodine ion. Oxygen likes to be a
08:00
2- minus ion. 2- and ion. And nitrogen has three negative charges. B- and we call that the nitrogen ion. Okay. This is a table where you see a couple of those
08:21
so-called elemental ions. What does that mean? These are ions that are formed from the elements. In a few slides we'll see another type of ion that is called polyatomic ions, which are ions that have multiple atoms together and the whole thing is charged. But this is only one part of the elemental particle which has a charge. It's missing or it has a charge.
08:46
All of these examples here are anions. Okay? So these are the elements, and these are the corresponding anions, and I show this table because these anions have what we call common names. So we can either call this the carbon ion
09:02
or carbide. So when you see the word carbide, you know we're talking about a C4 minus. That is a carbon ion. A silicon ion, this is silicon 4 minus, is sometimes called silicide
09:22
and this is nitride N-3. So we saw on the previous slide, it's a nitrogen ion, but the common name is nitride. The oxygen ion, oxide. Sulfur ion, sulfide. S2-. Selenium, selenide, Se2-.
09:42
And this is tellurium, telluride. And this is a negative charge of 2. Fluorine is fluoride in its ionic form. It's an anion with one negative charge. Chlorine becomes chloride, bromine, bromide, and iodine becomes iodide. So you see here some form of systematic in those common names. Yes.
10:12
For the cation, we don't have such common names. So for instance, the sodium ion is called the sodium ion. So this thing, this mechanism here holds for the elemental ions. For the ketone, we don't have such a
10:30
similar system. The potassium ion, the bromine, the barium ion, the calcium ion, we don't call that something like this.
10:42
So let's have a closer look at what is the charge of the elemental ion. How do I know? What is what? Now let's look at this table very quickly. You see here in blue those are what we call the nonmetals. The nonmetals.
11:02
And this light green here is what we call the metals. This gray area is the in-between area, or the metalloids. Now if you look at the charges, you see, this is all negative. So everything in this area where you see the metalloid, the tellurium, or these nonmetals, they tend to have negative charges
11:25
if the elements are in their ionic form. All the metals, as we can see, have positive charges in their ionic form. That's one observation. Here's another observation if you look carefully.
11:42
That is this. If you look at this column right here and this column right here, you see these charges are always the same. There's only one type of ion, but these guys seem to exist in multiple oxidation states, we call that. Which basically means it can be a different kind of charge. For instance,
12:03
chromium 2+, or chromium 3+. So there's several possibilities of the value for the charges that these elemental ions can have. We like to separate these two classes. The first class we call type I, which is a cation that always has the same charge. And the examples are found right here.
12:21
The first two columns, also aluminum, by the way, tends to have the same charge all the time. The other guys, which can have multiple types of charges, different values for the charges, which we call different oxidation states, which we will see later on in the class,
12:42
are called type II metals. Okay? So that means their cations can have different values for the charges. And the examples are found right here. So we have to be somewhat mindful of that. If a metal is type I or type II.
13:03
Okay. Here you see a list of type II cations. Iron, copper, cobalt, tin, lead, you see all of these guys can exist in several forms. Okay? They can have different values for the charges in the ionic form. Now importantly, the way we indicate that
13:23
is with this Roman numeral. And again, we will come back to this later on in a subsequent lecture when we try to give compound names, it turns out we have to be extremely mindful of whether or not it is a Roman numeral. All type II cations have the Roman numeral in their name. And if you forget to write that, you make a mistake. So we'll see how that goes.
13:53
Here's a list of common type II cations. Okay.
14:01
Now let's do the same kind of exercise we did at the very first slide, now with ions. Let's see if we can do this. So here I have this oxygen atom again, but now it has a negative charge. This is the oxygen ion. It has 17 again here, but now a negative charge of 2. How many protons, neutrons, electrons does this thing have?
14:24
6 what? 6 protons? 8 protons. Okay. It has, okay, let's hold on one second, one by one, okay, you guys are very eager to solve this puzzle. 8 protons, why? Because nothing has changed with the protons.
14:43
Nothing has changed with protons, so let's take 8. Number of neutrons has not changed. The only thing that has changed is the number of electrons. That's it. How many?
15:02
Aha. This is a great, great example. So let's go directly out of the way. It is not 6. This is 2-, it doesn't mean you subtract 2 from 8. Because you have two extra electrons.
15:21
Okay? You have an extra charge. Two extra electrons in addition to the 8 are already there. So you get 10 electrons. So be careful, this sign doesn't mean you have to subtract, it means two extra electrons on the particle. Okay. Another example, this is iron 3+.
15:43
I'll do this very quick. 26 protons, because 26 is the atomic number of iron. It wouldn't be 26, it would not be iron. It's the definition of iron. The definition of iron is the thing that has 26 protons. Number of neutrons subtract
16:00
26 from this number is 31. 31 neutrons Number of electrons. What do we have to do? Subtract or add? 23, yes. I think most people said 23. Exactly right. This one is missing. It's missing 3 electrons. That's why it's also the charge.
16:22
If it was neutral, it was 26. If it's missing 3, you subtract that number and you get 23. So basically, rule of thumb, the sign here is exactly what you should not be doing. Reverse that. Okay. Another question. What is the elemental symbol of this element
16:42
if it has 6 electrons? That is carbon, yes. Correct? This is neutral, okay? This means the number of electrons is equal to the number of protons. What is the number of protons? That is our brand, carbon.
17:05
Next one. Based on the information above, what is the elemental this is above? Symbol of this element if it has 4 electrons. So what is the symbol of this? It has 4 electrons. It's really the same kind of question.
17:22
4 electrons, it's neutral, let's talk about number 4, which element is that? Be. We call that beryllium. That's beryllium. Very good. How many electrons does potassium have? Can you say that very quickly? What is that?
17:40
19, yes. It is not charged. And that means that this number of protons is the same as the number of electrons, how about this? mondolimium. How many electrons does this ion of mondolimium have? Very good. 98. You guys get the hang of it. Subtract 3 from 101, which is the number of protons, the number of electrons is 98. Excellent.
18:08
You guys are nicely warmed up. I like that. Right? Yeah. Okay. Now we'll move on to another type of ion, which is not an elemental ion, it's just one single particle. One atom, if you want.
18:22
But a cluster of atoms together, which together has a negative charge. We call those holiotomic ions. Now these things have common names. They have common names. And here's a table that is
18:42
going to be important to us. And so you would give yourself a great service if you can recognize these and work with these. Does that mean you have to memorize them? Kind of. Yes. Basically you have to memorize them. You don't really necessarily have to, because on the exams
19:04
you are allowed to bring a 3x5 index card on which you can write everything you could possibly write. Which means you can put one symbol on there, or a lot, depending on the time you can write.
19:22
The bottom line is I don't want to force you guys in this class to just memorize things. I hate, in fact, that you would just take this class for memorization purposes. Memorization is not a rule. The worst way is to learn something, because it's a very short time. That means as soon as you do the exam, you walk out of the classroom, you tend to forget almost everything. Which makes my job completely useless.
19:46
Why am I spending three months with you guys if right after, the minute after you walk out of the door, you forget everything I ever talked about? Very sad. So memorization is not the key. I want you to first of all develop an appreciation for this stuff
20:03
because appreciation is something that usually sticks longer. Okay? If you like something, you feel like, eh, you know, not too bad, kind of cool, then you tend to actually retain it. So I like to do that. Some of these things will be good to retain. Okay? Rather than memorizing, retaining it would be good. Which means later on you can use these things.
20:25
If you recall the doctor, this is good. As a doctor, phosphate buffers are important. Carbonate blockers, too, by the way. So these things are actually real, and they play a role in our daily lives.
20:40
Okay. So let's go on with this. I'll go quickly through some of them not all of them, this is the only well, there's two actually, two cations, the rest are all anions, as you can see. And there is some systematic here. You see sulfite and sulfate they're very much alike you see here chloride,
21:00
chlorate hypochlorite, and perchlorate. And we'll see these things again. If you recognize, there's some systematic in the way these things are named. Okay. So we'll come back to that. So, we have met the ions.
21:24
We've also met atoms that are neutral. So now we're going to take a leap and see what happens when we put these guys together. Two things together to see what happens. Because chemistry is all about putting different atoms together, making bonds. So there's two
21:41
main ways, there's more ways than this, but these are the two main mechanisms by which two individual elemental particles, be it an ion or an atom, can make a bond. The first one is called the ionic bond. What is that? Well, you have two ions that are together. One is plus, one is minus.
22:03
What keeps them together? Electrostatic forces. Yeah. The fact that this is a plus and a minus, there's an electric force between them. The Coulomb force. It's called the Coulomb force.
22:21
So this is electrostatically bonded. Another type of bond is what we call covalent bonds. The covalent bond is not an ionic bond, which means this particle here and that particle here do not have different charges. Typically they are neutral.
22:40
This line in between is where the binding electrons are. So the binding electrons are shared as opposed to separated. The ions are separated and the covalent bonds, they are shared. I'll show another picture of that in a moment. First we're going to talk about the ionic bonds. All right, ionic bonds, some kind of, like, strange fluff floating around in space that we've never seen.
23:11
Salt is an ionic compound. One of the most common ones this is rock salt, sodium chloride. It's composed of sodium ions and chlorine ions that have decided to stick together and form a new compound.
23:28
Give me another example. Caustic soda. Okay? That is sodium hydroxide. It contains sodium ions once again, but now with a different anion. Not a chlorine, but a hydroxide anion. Which is a polyatomic anion.
23:45
So I swap this for that and you get a completely different material. Completely different material. Different properties, different kind of electricity, different kind of taste. It will be compared. Another example, please.
24:01
How about chalk? Who knows what chalk is? What is it? Well, I know what it is. You can use it for that. But what is it made of? What is it made of chemically? What is it made of chemically? You know what it is? What is it? Calcium carbonate.
24:25
Who is doing the Wikipedia right now? Okay. Calcium carbonate. Very good. Calcium 2 plus and carbonate 2 minus. This is a carbonate ion, a polyatomic anion. You see two ions together that form a compound. This is chalk. And there's like plenty of examples. I mean, all around compounds we call ionic.
24:50
So ionic compounds, cation and anion are held together by electrostatic forces, or we also call these forces coulombs. The coulomb force.
25:02
Okay. So how do we write formulas of ionic compounds properly? This is one of the things we should be able to do tonight for homework. Let me show you. The key is this. You have to form a neutral compound. That means zero charge.
25:22
You have to balance the charges. What does that mean? Well, let's look at calcium oxide. Calcium oxide, like the name suggests, contains calcium and oxygen ions. What are their corresponding ionic forms? Calcium is always existing as 2+. The oxygen ion is an anion, which always exists as 2-.
25:45
You put these guys together, it's going to be neutral. So if you add these guys up, you get calcium oxide, and that is neutral, which means this is correct. This is the correct formula.
26:00
Okay. Another example. Lithium oxide. Replace the calcium for a lithium ion. So lithium is the element, oxygen again, lithium likes to exist as 1+, not 2+. The oxygen ion is again 2-. It hasn't changed.
26:20
These charges are not the same. So if I add them up, I have a mismatch. What do I do? What would you do? How about this? Two lithiums. Two lithiums, one oxide, one oxygen ion, together are neutral.
26:42
And that's why the formula is lithium-2, oxygen, uno. One. You don't really write it in one. So there's one oxygen ion, and two lithium ions. All right! Very well. Now, let's do another few.
27:01
Let's do aluminum chloride and magnesium nitride. Same deal. Okay, aluminum chloride has two elements. Aluminum and chlorine. There they are. Aluminum forms 3+, always. Always 3+.
27:21
And chlorine is always Cl-. Aluminum is a type 1 metal, which means its charge is always the same. The charges are different. So in order to make this a neutral compound, I need three chlorines for each one aluminum.
27:42
So that becomes aluminum, chlorine, with a subscript 3. How about this one? Magnesium nitride. Magnesium, there it is, is a
28:03
magnesium 2+. Okay? It's always 2+. Nitride, as we've seen, forms, the nitrogen atom tends to form 3- anions. These charges are clearly different. So what do I do to make this neutral?
28:20
I cannot really multiply this with a certain number to make it the same as 2+. Or vice-versa. Yeah. Exactly. The suggestion is, why don't you multiply this by 3 and that by 2, then you actually have a total of 6 plus charges and 6 minus charges, that should cancel out. And that's exactly what happens.
28:41
You multiply this by 3 and that by 2 sorry, yeah, this by 2 and this by 3 and you get magnesium 3 and the nitrogen ion as a subscript of 2. Okay? So that's the key. You make it neutral, you make sure that you have the right multipliers such that the whole compound is neutral.
29:02
Okay. Now let's quickly look at those covalent bonds. We talked briefly about ionic bonds, we talked about those covalent bonds. Importantly, the difference between anionic bonds and covalent bonds is what happens to the electrons.
29:23
In anionic bonds, the electrons all the way here, for instance, on the anion is taken away from the cation, that's why this is a cross, this is a minus sign. That does not happen in a covalent bond. The binding electrons are shared among the atoms.
29:40
Here's an example. This is a single hydrogen atom. It has one electron. Here's the nucleus, that's the proton. If you put two of these fellows together, right here, then two electrons can actually sit in between the nuclei this is negative, sorry, this is positive, this is positive.
30:02
Two negative charges inside. The whole thing is going to be neutral. So these two electrons sit somewhere in the middle in a pretty favorable situation because they experience the attraction both from this guy as well as from this guy. So these electrons are belonging to this atom or to this atom, they are shared. That's why we can write them as columns. The single electron of
30:27
the hydrogen atom is now shared between two hydrogen atoms, and we can also write this guy as simply a line. This is
30:42
a tree. Somebody lets his- oh, this is not mine. It's like a root. It's a big step from chickens to animals. We'll try.
31:24
So this is no longer two atoms separate, it's now a molecule. Okay? So the hydrogen atom is right here, and this is what we call the hydrogen molecule. Two guys together sharing electrons. Form a covalent bond.
31:42
So, again, these are compounds that we can find over on us. Water is a covalent molecule. And what about methane?
32:04
methane is also a covalent linkage between carbon, in this case, and hydrogen, forming a methane molecule. Ca4. Here's a structure, this is another rendering of it. More sugar. Here it is. It's kind of like a complicated structure, it doesn't matter.
32:21
Each line here is a covalent linkage. Meaning, binding electrons are shared between the neighbors. Here's the overall formula. You see it's a much more complicated molecule. That's 12 carbons, 22 hydrogens, and 11 oxygens organized in this structure.
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Here's another chart of, you know, ways in which we can depict covalent linkages or compounds that contain covalent linkages. So here's a water molecule again. This is one way to write it. An oxygen and two lines, indicating a covalent bond, and then the hydrogen, and the hydrogen.
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Or a covalent stick model. Or a space building model. These are all renderings of the same thing. So if you recognize these in books, it really means these are covalent compounds. Ammonia is an example, methane we just saw on the previous page, and also the hydrogen molecule. Two hydrogen atoms together. This is the simplest molecule. A hydrogen molecule.
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All right. So now we have an important question that we have to answer. When do we speak of an ionic bond? And when a molecular bond or a covalent bond? Can I tell? Can I look at the formula and say, ah, this is a covalent compound. Or, this is an ionic bond. How can I tell that? Yes. Okay. I'll take over,
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take over, I'm going to sit here. Great. Really good. Okay, so an ionic bond is formed between a metal and a nonmetal, a metalloid.
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And a molecular bond is between two nonmetals. So both elements have to be in a nonmetal. Basically, if you have one metallic compound in there,
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and something is not a metal, you have an ionic compound, an ionic compound, if both of them are not metal, then it is a covalent compound. Okay, so here's this table again, with the proper coloring. meaning this green is metals
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the metalloids are right there and the nonmetals, again, in blue. Hydrogen is considered a nonmetal. So when I make a compound that is formed only from elements in this area right here, plus this, then it must be a covalent compound, meaning a molecular compound.
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If it's made of something that comes from here, plus another element that comes from this corner, then I speak of an ionic compound. Let's see if we can identify all the compounds in which the bonding is predominantly covalent.
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So which ones of these are the covalent compounds? How about this guy? Is that covalent or ionic? Who says ionic?
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A few folks. Who says covalent? All right. It is covalent. Why? This is boron. Boron sits right there. It is not a metal, chlorine sits there, no matter. Two nonmetals, meaning this is covalent. How about boron fluoride?
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Actually, it's boron trifluoride. Boron trifluoride is covalent, yes. How about this? Arsenic sits right there, chlorine again in this column right there, this is also covalent. How about iron sulfide? Ionic. Yes. Ionic because iron evidently is a
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metal, it sits right here, it's green, sulfide is a sulfur atom, it sits right there. This must be ionic, and therefore is not covalent, it gets a red cross. All right? One more.
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Now we have to mark all the components in which the bonding is predominantly ionic. So which one of these are ionic? How about this formula right here? Is it ionic? No. It's not ionic because both oxygen and fluorine are not metals. How about this? This is ozone, by the way.
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Ozone is not a metal, it has no metal elements in it, but this is definitely not an ionic compound. How about this? Rubidium telluride. Yes, because rubidium here is right there. That is a metal. Telluride is metalloid right there. So it's a combination of a metal and a metalloid, that is an ionic compound.
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How about this? Phosphorus trichloride. No. It's not an ionic compound. Phosphorus sits right there, chlorine once again sits here, both are blue, this is definitely not an ionic compound.
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All right? You feel confident? Are you guys ready for homework tonight? Eleven o'clock. See you next week.