PRINCIPLES OF ALCHEMY WATER Some symbols and hieroglyphics of molecules. Lewis explains electron shells and the Strong Bonds. Covalent bonds - the sharing of electrons. Lewis Structures are diagrams of outer electron shells. Electrovalent (ionic) bonds - the give and take of electrons. Metal bonds - wandering electrons. The weak "bonds" (or forces) dominate the way molecules interact. Weak interactions determine the states of matter. VSEPR theory explains the shape of covalent molecules. Other molecules use electrostatics to make their simple shapes.

Three quarters of the world's surface is covered by water. Without water life itself would be impossible. And most Alchemy occurs in water.

Yes, I suppose you would. At least the bulk of it. Today I want to tell you how atoms link-up into important groups of atoms called molecules. Water is a perfect example of this next level of Alchemy. Water is my favorite molecule.

A molecule is a combination of two or more atoms bonded together. They can be the same element like two hydrogen atoms. We call that an "elemental molecule". Or a molecule can be made of different elements like an oxygen atom and a couple hydrogen atoms to make a molecule of water. Molecules made of a mix of different elements, are called "compound molecules"

Yes. But a proper Alchemist would call two bonded hydrogen atoms an "elemental" molecule. Notice the "al" at the end. It makes it sound better.

No. That would sound ridiculous.

Precisely. It is important to understand that when I speak of hydrogen I could be speaking of just a single atom of hydrogen (like our previous lesson) OR I could be speaking of the molecule of hydrogen made of two hydrogen atoms bonded together.

What do you think?

Right you are. Most of the time we think of molecules with elements of single isotopes. But there are mixes of molecules with different isotopes. They are found in nature and can be made by clever Alchemists.

Yes, exactly. That's an important point!
Molecules are made of atoms and atoms have atomic masses. So molecules have molecular masses.

They certainly do. Sometimes Alchemists talk about molecular mass as if they were dealing with "pure" molecules -each element a single isotope. But most of the time, Alchemists actually work with molecules that are a "mix" of isotopes.

Yes, usually. And, of course, the average molecular mass is (almost always) a number with decimals and fractions.

Take water. It has two hydrogen atoms and one oxygen. Most of the time those hydrogens are simply normal hydrogens with an atomic mass of one. And the oxygen atom is usually oxygen's most common isotope with an atomic mass of 16.

Yes, well done. All you need to do to find the molecular mass of a molecule is to add up the atomic masses. But the AVERAGE molecular mass of water is 18.015. Do you know why?

That's right. When calculating the average molecular mass you add together each element's average atomic mass. Hydrogen's average atomic mass is 1.008.

That's' right. Now here is a wee riddle.
If you understand what I've told you about average molecular mass, you should be able to tell me, what is the average ATOMIC mass of the oxygen in water molecules.

Very good, Arthur. It is really just a matter of keeping track of the atoms that make the molecules.
18.015 is the average molecular mass of water
-2.016 for the average atomic masses of two hydrogen atoms. Leaves
---------------------------------
15.999 for the average atomic mass of oxygen.

Yes, they are but compounds like water are more exciting. A compound, being made of more than one type of atom, will have a name of its own (or it should).

Aye. Water is made of oxygen and hydrogen atoms. When I speak of water, I could mean just one molecule of water or buckets of water. Either way, what I say about the chemistry of water applies to all water. But if you break water down into its elements (its atoms including their isotopes) it is no longer a molecule and no longer a compound. When you break up a compound you get more than one kind of element. And what you get is not water, nor does it behave like water anymore. On the other hand, when you break up an elemental molecule you get all the same elements (although they may be of different isotopes) and they all behave the same because they are made of all the same kinds of atoms (elements).

Yes, they are. We have ways of keeping track of that complexity. The most important being how we write and talk about molecules. We describe molecules by the atoms which are used to make them. By writing the atoms and the numbers of them in each molecule, we have a formula for that molecule.

Yes. Exactly. We use the same abbreviations, but we arrange them and number them to show how the atoms are grouped to make the molecules.

Let's take water as an example. Water is a molecule made of two hydrogen atoms and one oxygen atom. We use the symbol "O" for oxygen. Water, then, is just the abbreviation of two hydrogen atoms and one oxygen atom.

Yes. Sort of. Actually, we use subscripts to designate the number of each atom (element) in the molecule. A subscript is a number written slightly below the script. So instead of writing "HHO", we write "H₂O". The formula for water is H₂O.

Well, I suppose you could, but that would make it needlessly more complicated. We assume the one (1) is there whenever we don't see it! If you know what I mean.

That's right. If there is only one of that atom in the molecule, we just drop the number one from the molecular formula and make believe it is there.

Right. That would get very difficult after a while. There are about a hundred different elements. You don't want to write a formula with all those zeros in it do you? It would be a waste of time.

Yes.
Consider the elemental molecule, hydrogen. It is just two hydrogen atoms. Write the number two (2) as a subscript, right after the H, to make it clear. (H₂)
When writing a molecular formula, always write the number of atoms (greater than 1) behind and slightly below (subscript to) each element's abbreviation. This will represent the number of each element in the molecule. By "number" I mean, of course, the number of actual atoms of that element in the molecule, not the "atomic number". OK?

No. That would sound like something else.
Can you think of what we might confuse that with?

That's right. So instead of saying "hydrogen two, oxygen", we say "H two O". Just use the abbreviations. It is very important to understand that difference. Otherwise you will be confused about whether the number of an atom in a molecule is an isotope or the number of atoms of that element. Do you see what I mean?

You got it! It's easy enough to see the difference when you write it all down (like this). But when you are having a conversation it is important to keep clear whether you are talking about the number of nucleons in the atom or the number of atoms in the molecule.

You sure can but it is a rare molecule. Remember how rare deuterium is compared to normal hydrogen?

Precisely. But just because it's rare doesn't mean it's impossible. Water made of deuterium atoms, instead of normal hydrogen atoms is called "heavy water". Can you guess why?

Yes exactly. Now tell me, how would you write the formula for heavy water?

Yes. "²H₂O" is the formula for heavy water. We call that "upper left" two (2) a "superscript" because it is above the rest of the script.
Now. How would you say the formula for heavy water?

Right, and.....

It is right, but you notice it is not very easy to say the formula. It's easier to write it. Don't you agree?

Well, most people don't bother. Because it is so confusing.

I don't waste your time. I teach and you learn. Your description of heavy water as "hydrogen two, H two O" is a good description and any Alchemist would understand what you mean. But it is a mouthful, isn't it?

These formulas are important and easy to master. Your description of heavy water is a fine example of your ability to understand the way we Alchemists talk.
Lets' try another one. How would you write the formula for a molecule with a carbon and four hydrogens? By the way, carbon is abbreviated "C".

Yes. That is good enough. But tell me, would it be any different to call it "C H four"?

That's right. They are the same. As it turns out, we Alchemists like to write it "CH₄" and call it "C H four".

It makes sense either way. It's just that Alchemists tend to put the hydrogen at the end. Probably because it is so small. But not always.

Water is an exception. And there are a few others.

Now, now Arthur. I know you have the intelligence to remember that water is "H₂O" and not "OH₂". Even though they mean the same thing.

"We guys" have some complex rules. They aren't twisted. In fact, there are very specific rules about how to put the elements in the correct order. But that is an advanced subject. I don't want to go into that now. It has to do with electronegativity and the periodic table.

Why not just remember to put the hydrogen at the end and remember that water is an exception? It doesn't really matter. "H₂O" and "OH₂" are the same formula. Just rearranged. And "CH₄" is the same as "H₄C". OK?

Electrons.

Yes. Electrons are what we will focus on today. As a matter of fact, electrons are the focus of most of Alchemy.
Electrons hold the atoms to each other. They are the glue that makes molecules - both elemental and compound ones. And they are responsible for ALL chemical reactions!

No. Remember beta decay is an ATOMIC reaction, not a CHEMICAL reaction. True, it produces an electron, but beta decay is not a chemical reaction. In our last lesson I taught you about atomic reactions because they are involved in transmutations, the transformation of one kind of one atom into another (by changing the number of protons).
But in chemical reactions none of that occurs. Chemical reactions never change the atoms, just the way they are bound together (or "bonded" together). And they are bound together by the electrons.

Yes, that's a good way to express it. Try to imagine a group of ships linked together by chains. Each ship is the nucleus of an atom and the chains are the electrons responsible for holding them together.

Yes, they can be imagined that way, if you like. If all the ships are the same (all the atoms have the same atomic number) then the fleet is an elemental molecule. If even one ship in the fleet is different, it's a compound.

That depends on the kind of bond. Like metal chains, electron bonds come in different types and have different properties and different strengths. Chemical reactions are the breaking of these electron chains and reforming them with other atoms, often in other patterns.

Yes! By understanding how these electron chains are made and how they behave, you will understand Alchemy!

The trick to understanding how electrons form bonds is to understand electron shells.

Good.
You'll recall that the K-shell is a small shell and can only hold two electrons. For hydrogen or helium that's all the shell room you need. So hydrogen and helium are limited to using only those two electrons for bonding. They only have a K-shell.

Yes, exactly. And that "room for two more" is very important, as you will see in a moment.
Four years after Bohr told the world his idea, an American Alchemist named Lewis explained that atoms try to obtain a full outer shell of electrons. Lewis' idea is also based on quantum mechanics. He showed that atoms try to fill their outer shell with the maximum number of electrons allowed for that shell.

Yes, I suppose. Bohr came up with the idea of the "modern atom". Bohr used quantum mechanics to show that electrons are CONFINED to SHELLS. But Lewis came up with the idea that atoms want COMPLETE OUTER SHELLS. It is this "desire" by the atoms to have a complete outer shell that causes the strongest bonds to form.

Precisely. We say the shell is "not closed" or "not complete" when there is still room for more electrons. Atoms like to have closed shells, where each shell is filled with its maximum number of electrons. It's a quantum mechanical thing.

Yes. Oxygen wants two more electrons to complete its outer shell. But wouldn't that be a problem?

Yes. And it is precisely this "problem" that causes bonds to be formed.

Atoms seek to fill their outer shells. Exactly how they do that depends on the number of protons it has.

Right.
Some atoms form a complete outer shell by stealing electrons and becoming negatively charged ions.
Other atoms give away electrons in order to turn their complete inner shell into an outer shell.
And other atoms borrowing electrons to complete their shells.
Atoms will do almost anything to have a complete outer shell!

That depends on the atom itself. And that depends on the number of protons it has.

Right again.

Yes and no.

What do orbitals determine about an atom?

Precisely. We'll come back to orbital shapes near the end of this Ancient Element when I teach you about the shapes of molecules.

Aye, they do.

Yes and no.

Spin gives some molecules very interesting properties and can be useful when learning about very advanced forms of bonding. But for our purposes, we'll ignore spin.

Aye.

Ah, wait a minute. About the M-shell. You are right, it CAN hold 18 electrons, but it doesn't like to.

You may recall that the M-shell has d orbitals. (Remember the last question in AIR?)

That's true, you're absolutely right. You CAN squeeze them in. But atoms are, well, reluctant to use their d and f orbitals. Instead they use the s orbital, and even the p orbitals, of the next largest shell.

It has to do with quantum mech...

Well, you don't need to know why. But you should know that the d orbitals in a shell are only used AFTER the s orbital of the NEXT shell are full. And the f orbitals in a shell are only used AFTER the s and p orbitals of the NEXT shell are full.

Yes and no.

Now calm down, Arthur. We won't be discussing those d and f orbitals in this Ancient Element anyway. Atoms don't start using their d and f orbitals until they have lots more electrons. The really big atoms do that. For our purposes we can limit ourselves to a simplified view of shells. So there's no real reason to get all upset.

Well, I just told you that it doesn't want to use its d orbitals, so how many electrons will it "want" to take?

Right. That wasn't so hard now was it?

Aye, that's what it means.

Aye.

Yes.
Tell me Arthur, if atoms are so quick to use the next outer shell's s and p orbitals, before using their own d and f orbitals, what will be the two possible orbitals on the outside of any atom?

Right!
Think of a series of atoms, each one with one more electron (and proton) as the one before it. You would see that before any atom placed an electron into its d (or f) orbital, it would first fill its s (and p) orbitals in the next shell.

That's right! That's exactly right. The outside of all atoms is made of only s and p orbitals. No matter what shell you speak about, (except the K-shell which only has an s orbital.)...

Aye, it does!
You see, most of the action of Alchemy occurs with the outer shell. The outer shell determines the size of an atom and its shape. It is the outer shell that is responsible for all the bonding too. Those complex d and f orbitals don't get involved in those interesting properties (directly).

Aye. Except don't forget that the K-shell has only an s orbital. That's important if you are dealing with hydrogen and helium atoms.

Right again!

Well, I wouldn't go that far. You need to keep them in mind for some things. After all, they are a place to put the electrons you need to keep a balanced charge.

Right.

What? How do you mean?

Hmm. I hadn't thought about it that way before, but you are right.
I like that - d and f orbitals are the "basement" of the big shells.
Very good, Arthur. Well said!

I agree! Any outer shell holds up to 8 electrons. (Except hydrogen and helium, because their K-shell only holds 2 electrons in the s orbital.)

Water is held together by hydrogen and oxygen SHARING electrons, forming covalent bonds.
In a covalent bond, electrons are swapped rapidly back and forth between the two atoms.

From another hydrogen. Water is made of one oxygen atom and two hydrogen atoms. By sharing the electrons, both the hydrogens and the oxygen will have complete shells. Can you describe that? Work from the inside outward, filling the shells as you go.

And what about the hydrogen's K-shell?

Yes. That's right. But that makes the K-shell incomplete too. The K-shell must have two electrons to be full. Where does it get them?

Yes. Very good! Hydrogen swaps around electrons and, at least some of the time, it has two electrons in its K-shell.

Yes. Let's draw that. Go ahead and count the (red) electrons. I'll circle the shared electrons in blue. Remember to count them each time for each shell. Yeap! The oxygen has six of its own electrons in its outer shell and borrows an electron from both hydrogens to complete its L-shell. At the same time the hydrogens complete their K-shells by borrowing an electron from the oxygen. Right. All three atoms in water have complete outer shells by sharing their electrons as covalent bonds. Each covalent bond is caused by two electrons being shared between two atoms.

Hey, wait. I just counted them again. I see a total of ten electrons, not eight. When you count the shared electrons, the oxygen has ten electrons. Two are shared, but doesn't that make the oxygen charged?

You've confused yourself on the counting. It's a common problem.
First of all, you only count the OUTER shell electrons when working with bonds. Oxygen has six outer electrons of its own and it shares two from the hydrogens for a total of eight electrons in oxygen's outer shell, not ten.

Right. It's a common mistake. Just remember to think only about the outer shell when determining bonds.

Right. But you may be getting these two ideas confused. When you count all the electrons in the entire system of all three atoms, you must also count all the protons!

If all you are concerned about is the charge of the water molecule (not just the bonding) then go ahead and count the inner and outer electrons. But also count all the protons.

Yes, I think you've got it
If you want to know the charge on something you must take ALL of it into account. That's different from bonding. Bonding only depends on the outer electrons.

Yes. That's a molecule of water. That's what rain is made of. And ice and steam! Think about a covalent molecule as a system of electrons being shared. Notice that when these three atoms (two elements) share their electrons, the final water molecule has no charge and all the shells are filled.

Oh yes indeed! Most molecules are held together by covalent bonds and their chemical reactions depend upon the way these bonds are broken and reformed. Keep these two simple steps in mind:
1. Fill the shells from the inside out, start with the K-shell and move outward, trying to leave behind filled shells.
2. Try to think of a way of sharing pairs of electrons between atoms in order to fill the outer shells. That makes the covalent bonds.

Yes, it is. So puzzle this. What would hydrogen do without the oxygen?

Well, it has only one electron in its K-shell (its only shell), so it needs another electron. I guess it gets one from another hydrogen atom. You guess right! Hydrogen shares its sole electron with another hydrogen, which shares its sole electron too! Kind of like borrowing from Peter to pay Paul, isn't it?

I like to think of it as two atoms obtaining the same goal (complete shells) by sharing.

That's right. Under standard conditions, like you find here around us, hydrogen is a molecule of two hydrogen atoms sharing their two electrons and thus satisfying their requirements to have complete K-shells.
We say that the hydrogen molecule is a diatomic molecule, meaning it has two atoms. And it is an elemental molecule, too.
On the other hand, water is a triatomic molecule because it is made of three atoms. And because water is made of more than one element, it is a compound molecule.
Now here's a question for you. How would you write the formula for a molecule of hydrogen?

Right. That shows us we are dealing with molecular hydrogen (H₂) and not atomic hydrogen (H). Get it?

What about helium?! You tell me.

Helium has two protons so it has two electrons to balance the charge. But that would mean that it already has a complete K-shell (because the K-shell only holds two electrons). So it doesn't need to share electrons, it has all it needs. Exactly two. Helium wouldn't need to make a covalent bond.

And it doesn't. Helium is monatomic. Just one atom and that's it. It's not even a molecule. It shares no electrons and makes no bonds. We say helium is "inert", meaning it is unwilling or unable to do anything. It can't form bonds so it can't form molecules or even take part in a chemical reaction! Its formula is simply "He". Always! It can't be anything else.

Yes, that's a good way to look at it. Because inert elements do nothing and seem happy to be away from the rest of chemistry, we sometimes call them the "noble elements"!

Who me? Not at all. Not at all.
There are six inert or noble elements. Helium is the smallest and most common one. The next largest is neon (Ne). If you have been paying attention to what I said about noble elements and their electron configuration, you should be able to figure out neon's atomic number.

You can. Precisely what have I told you about neon?

Yes. And what have I just told you about the electronic configuration of all noble elements.

Excellent! You are well on your way to understanding Alchemy. Most of Alchemy is keeping track of the electrons. You can learn a lot from electrons. Normally, Alchemists don't go about figuring out atomic numbers in this way. But the logic you used to arrive at your answer is exactly what Alchemists do! We use fundamental ideas, like Bohr's atom and Lewis' shells, to figure out such things as the behavior of atoms and molecules.

Yes, but we'll talk about them later.
Time for a quick review. Tell me what you have learned about the bonding in molecules.

Yes. That is absolutely right. And .....

Yes. Helium and neon are inert elements because they can't become a molecule or perform a chemical reaction. Their outer shells are complete. To share electrons, they would break the rule of trying for a complete shell.

I agree.
Don't forget, a complete shell is the "electronic configuration" that all atoms seek.
Some, like helium and neon, are "born" that way, like nobleman.
Other atoms that do not have these stable configurations seek to obtain them in many ways. Sharing electrons, and thus forming covalent bonds, is a common way to do that.

And all this is understood thanks to Bohr?

Yes, with help from Lewis.
In fact, Lewis introduced an easy method for keeping track of electronic configurations which is very helpful when trying to figure out covalent bonds. They're called "Lewis structures".

Lewis structures. We represent the atoms by their abbreviations and add dots or crosses to represent the electrons in their outer shells. Only the outer shell electrons are important, so that's all we draw. Pairs of shared electrons are placed between the two atoms and are counted towards the electronic configuration of each atom. Each of those Lewis pairs is a covalent bond.

The trick is to draw the Lewis structures such that they end up having the electronic structure of a noble gas. That is, to give it a full outer shell.

No. The electrons are identical. We just use different symbols to help keep track of which atom is sharing which electrons. But in fact, the shared electrons are the same. After all, there's only one kind of electron! Each covalent bond, each pair of shared electrons, is made of one dot and one cross.

Yes. Precisely.
The atoms are linked by the sharing of electrons. Each donates an electron and accepts an electron.

Yes, I think you do. Can you draw and explain a Lewis structure for diatomic oxygen?

Right! As a matter of fact, you can write the formula for (diatomic) molecular oxygen as "O₂". Just like for the hydrogen molecule ("H₂").

Yes.

Well, strictly speaking, the L doesn't stand for Lewis. It's just the next letter after K. OK?

Right.

Oh, now think about it Arthur. Think about how the two oxygens might share their outer electrons so as to "satisfy" their "need" for a complete L-shell.

It sure can - if it is doing it to satisfy its need for a complete shell. Remember the water molecule? Oxygen shared 2 electrons. One to each hydrogen atom.

Oh, yeah. So, oxygen can share 2 electrons with another oxygen. And that oxygen can share two, too! That's right. So, diatomic oxygen is a (elemental) molecule made of two oxygen atoms sharing TWO PAIRS of electrons. Yes. Exactly. Diatomic oxygen is formed by sharing of two pairs of electrons. So how many covalent bonds does it have? Two covalent bonds! One for each pair of shared electrons. Yes, we Alchemists would say each oxygen atom has a "covalency" of two. Hydrogen has a "covalency" of only one.

Precisely. Notice that it takes the sharing of TWO electrons to make each covalent bond. If two elements form a molecule by sharing two electrons we say they have one covalent bond between them.

Yes, it is. Hydrogen has a covalency of one because it forms one bond, but oxygen has a covalency of two because it forms two covalent bonds.
Try another one. How about the molecule, diatomic nitrogen?

Oh, yes. You need to know that nitrogen has an atomic number of 7. And we abbreviate it with an "N". We write molecular nitrogen as "N₂", because it is made of just two nitrogen atoms.

Yes, I know. At least that's the "magic" Lewis number for the L-shell.
For the K-shell, the "magic" Lewis number is 2.
Now. How do you think the pair of nitrogens go about filling their L-shells?

By each sharing 3 electrons with each other, a total of 6 shared electrons! They form 3 pairs of shared electrons or 3 covalent bonds. Nitrogen has a covalency of three! Six electrons are shared in total. Very good. The bond between these two nitrogens is actually made of three bonds. We call that a triple bond.

And you would be right! N₂ is a very difficult molecule to pull apart because of the triple bond. And nitrogen atoms are well suited to make them. Notice that the number of bonds (the covalency) changes among the elements as we need to satisfy the rule of "completing the outer shell". These shared electrons ALWAYS come from the outer shell. The electrons buried deep in the K-shell aren't available for sharing. Unless they are the only electrons.

Yes, that's right. Hydrogen's sole electron must be in the K-shell and it is the only one available. But I want you to understand that in the bigger atoms, with multiple shells, it is only the electrons in the outer most shell that can be shared. The others are buried too deep.
Also notice that because hydrogen only has one electron to share, it can only form single bonds.

Yes, H₂ is one of the easiest to pull apart.
But be warned. A great deal of this "weaker/stronger" comparison can be misleading. Sometimes it is a simple matter of counting bonds (single versus double versus triple). But there are other factors to consider when talking about making and breaking bonds. Like, what will be made once the bonds are broken? What will be produced from the broken bonds is very important. But this takes us into the realm of chemical reactions and I'm saving the best for last. We'll talk about that when we get to the last Ancient Element, "FIRE".

Well, that depends on how you define "best". The element that forms the MOST covalent bonds is carbon. Carbon has an atomic number of 6. Tell me about its electronic structure and how it forms covalent bonds.

No. Not yet. Under most conditions, the molecules we talk about have no net charge. Unless I tell you otherwise.

Anyway, carbon would have 2 electrons in its K-shell and the remaining 4 electrons in its L-shell. So carbon needs 4 more electrons to give it a complete L-shell. I suppose it gets them by sharing. Forming 4 covalent bonds. That's right. Carbon has 4 electrons to share and needs 4 electrons to complete its L-shell. So it can form 4 covalent bonds. Carbon has a covalency of four. Does it get the other electrons from other carbons?

Yes, it can. Or it can get them from other atoms. Carbon is VERY versatile in its ability to make covalent bonds. There is a whole branch of chemistry that studies nothing but the bonding of carbons with other atoms, including other carbons. It's called Organic Alchemy and the molecules carbon makes are called organic molecules. Let's see if you can describe the simplest organic molecule - methane.

Methane is made of just one carbon and four hydrogens. CH₄. Can you explain its electronic structure?

Sure can. Carbon needs four electrons to complete its L-shell and it will make four covalent bonds to do it. Carbon will share its four electrons to make those bonds, one to each hydrogen. And each hydrogen will share its sole electron with the carbon. So methane is made of a single carbon with four covalent bonds, one to each of four hydrogens. That way the carbon fills its L-shell (taking on the electronic configuration of a noble element). And all 4 of the hydrogens get to share an electron from the carbon, so they can have a complete K-shell (taking on the electron configuration of helium). That's right. Methane has four covalent bonds. Each bond is a "carbon - hydrogen bond". Or simply a "C-H bond". A single covalent bond joins each hydrogen to a central carbon atom, in methane.

Neither! You've gotten confused about the molecules and the atoms that make them. It's a common mistake for students. The molecule doesn't have a covalency, only its atoms have covalency. Methane (CH₄), is made of one carbon atom with a covalency of four and four hydrogen atoms each with a covalency of one. Methane doesn't have covalency, but its atoms do.

Methane is a gas and a great source of fire! But, we'll talk about that in a later lesson. How about one more covalent structure?

Last one. For now, anyway. I promise. Tell me the electronic configuration of carbon dioxide. It's another gas. It's made of a carbon with two oxygens. "di" means "two" and "oxide" is just a way to say it has oxygens attached. "carbon di oxide" is "carbon with two oxygens".

So is water, but you managed that. Give it a try.

The carbon will try to form 4 covalent bonds by sharing its four electrons. (Because carbon has a covalency of four.) And both oxygens will try to share two electrons, to fill their L-shell. (Oxygen has a covalency of two.) So both oxygen atoms will each form two covalent bonds. Hmm.... My guess is that the carbon forms two covalent bonds with each oxygen. That way everybody is happy. Like this "O=C=O".

Yes. The carbon will share all four of its outer electrons, just like it does for methane. But in this molecule, instead of forming bonds with four hydrogens (one bond to each), the carbon forms two covalent bonds to each oxygen.

Yes. A great name for them.

Yes. I think you've got it now. But before we leave the subject of covalent bonds we should have a bit of a review.
You may not have known it but you have described most of the molecules in the atmosphere - the air we breathe.

True. But these things tend to over lap. The last lesson focused on atomic structure and I used the "air of the universe" to explain the details of hydrogen and helium. Now seems like a good time to explain the air in our planet's atmosphere. Are you ready?

Yeah, I'll let you have it! Here it is.
The atmosphere is a mix of molecules.
Diatomic nitrogen, or simply molecular nitrogen, (N₂), "N two" makes up about 80% of the air.
Diatomic oxygen (molecular oxygen), O₂, "O two" makes up another 20% or so.

Yes. There's a trace of some of the other gases we've been discussing.
There are traces of carbon dioxide (CO₂) and methane (CH₄).

Well, no. Actually there are traces of water in the air too.

Well, sort of. Rain is actually a clump of water molecules. We will talk about that later. What I mean by water in the air is what we call "humidity". The amount of water in the air varies a lot. More on that later.

Yes, a mix of different molecules. And I think we have now completed what I wanted to teach you about covalent bonds. Tell me what you learned.

Yes. But where does each electron come from? And why do they share them?

His name is Bohr. Not Boring!

Yes. It seems to. The two atoms in a covalent bond swap the two electrons rapidly back and forth to try to satisfy their need for a full outer shell. What about helium and its K-shell.

You guess right. And what of the other atoms we talked about?

Yes. Tell me which covalent molecules you can make with those atoms (hydrogen, helium and oxygen).

Just checking your understanding.

Yes. And what about nitrogen and carbon?

Actually, carbon has trouble bonding to just one of itself. It's too difficult to share 4 pairs of electrons (8 electrons!) between only two atoms.

Yes! Juggling 8 electrons (4 pairs making 4 covalent bonds) between two atoms is too difficult. But sharing them among more atoms seems to be easier.

Yes. Carbon can bond to other carbons - two, three or even four at a time. And those four can bond to more and so on and so on. That's why I call carbon the "King of Covalent Bonds". Because it is the best at making covalent bonds.

That's right. It is not noble, so don't get yourself confused just because I called it a "King". Now, what about nitrogen?

Excellent. Notice that N₂ manages to juggle 3 pairs of electrons to form 3 covalent bonds. There are many other molecules one can make, but we will leave them for some other time. Any last thoughts about these bonds?

Yes, that's a good way to think about it. But neither side wins. At least not in a covalent bond. If one of the atoms actually did pull away an electron and keep it, we would be left with two ions. That's how the next type of bond I want to tell you about is formed - ionic bonds.

Yes! In an ionic bond, one atom gives up an electron and another atom accepts it. The two atoms are then ions. One with a positive charge and one with a negative charge. And what do you remember about opposite charges?

Yes. Opposites attract! That is a fundamental law of the universe.

Well, I don't believe the universal law of "opposite attraction" applies to the behavior of people! But it definitely applies to atoms and molecules with an opposite CHARGE.

Actually, it is because they have lost or gained an electron that they are attracted to each other. It is the loss and gain of the electron that creates their opposite charges and it's the opposite charges that cause the attraction.

Well, try to remember that we are talking about atoms not people. The atom that got the extra electron will now have a negative charge, because it has an extra electron. We call this negatively charged ion an "anion". The atom that lost its electron will now have a positive charge (because it has more protons than electrons) and we call it a "cation". Can you remember that?

I get it.

Fine. If that works for you, then use it!

Aye. And it is the electrostatic forces that hold them together and form the ionic bond.

Electrostatic force is the force that causes oppositely charged particles to attract. It's just another way of saying what we have just been talking about. All I've done is give it a proper name. It is a "force" that holds them together. The force is the bond. And it has to do with the differences in their electric charges that we think of as "electro".

"Static" refers to the fact that the electrons don't travel very far. Static means stationary. So we say that an "electrostatic force" holds the atoms together in an ionic bond, rather than explain it each time as the attraction of oppositely charged particles.

I'm teaching you the language of Alchemy! And while we are on the subject, we sometimes call these ionic bonds, "electrovalent bonds". That way their name has an immediate parallel to covalent bonds. "Valent" is just another word for bond-electrons. Get it.

Very well put Arthur! All the compounds we discussed earlier were covalent compounds. But the ones we are now going to learn about are electrovalent compounds.
You see, some atoms are more likely to take or give away electrons than to share them. It depends upon how much they "want" the electron or not. And we can predict their behavior by recalling Lewis' idea about atoms trying to reach a "noble electronic configuration".

Yes, exactly. The elements we have been talking about so far have electronic structures that cause them to share their electrons. Oxygen (O), nitrogen (N), hydrogen (H) and carbon (C) usually share their electrons, rather than stealing them or giving them away.

Ah, yes. It depends one what other atoms are doing to them. Take hydrogen for example.

Yes, it does, with oxygen or nitrogen. But it doesn't share an electron with fluorine (F). Hydrogen gives its electron away to fluorine. Tell me what would happen to the hydrogen if it gave up its electron (instead of sharing it).

That's right. And it would be attracted to any anion (ions with a negative charge).

Good question. It's because fluorine doesn't want to share! And the reason fluorine doesn't share is due to its electronic structure. It has to do with its shells. Fluorine has an atomic number of 9. Tell me its shell structure.

OK. It has 9 protons and 9 electrons...... Yes, to begin with. But that will change. However, you are right to begin your thinking by starting with a neutral atom. Now where do those electrons go. Ah, 2 into the K-shell and the remaining 7 into the L-shell. It only needs one more to complete its shell.

Yes, that's absolutely right. It only needs one. That is why it STEALS the electron away rather than sharing it. Of course, by stealing away hydrogen's electron, the fluorine takes on a negative charge, becoming an anion. And the hydrogen becomes a cation, because it is now just a proton.

Exactly! A molecule of hydrogen fluoride (HF) is formed. It is an electrovalent compound.

Oh yes. Lithium for example. Lithium (Li) has an atomic number of 3. Tell me about it.

Right. If it were to give up that single outer electron (to fluorine, for example), what electronic configuration would that lithium ion have?

Yes, exactly! And that is "favorable" to the lithium ion. So the lithium is "happy" to give away its third electron.
By the way, we have a special way to abbreviate ions. It helps us keep track of the charges and which atom carries them. We put a "+" or "-" as a superscript, after the element's abbreviation to show that it is an ion. The lithium ion we have been discussing is written "Li⁺".

Very good.
By the way, some folks actually write a zero charge on atoms to remind them that they are working with neutral atoms. Like Li⁰, to show it is neutral lithium with all its electrons in place. But that gets a bit cramped in the molecular formulas, so I like to leave neutral "charges" out. Most of the time.

Yes, it is. But instead of describing fluorine as "grabby" we say fluorine has great "electronegativity". That means it is ready, willing and able to steal an electron. The more electronegative an atom, the more likely it is to steal an electron than to share it. Fluorine has a very good electronegativity but hydrogen and lithium have very bad electronegativity.

Well, we Alchemists don't really use that word. Even though it would be a good description. However, just to keep it all clear and sounding like a professional, let's just say that hydrogen and lithium have poor electronegativity. OK?

Yes, it is. And that was well said.
We can write all this out in an equation. It helps to understand what is going on
Li -----> Li ⁺ + e^- and that electron goes to the fluorine like this
F + e^- -----> F^- and then the two oppositely charged atoms are drawn together by the electrostatic forces to form LiF.
Notice two things. This molecule has no net charge because the two ions cancel each other out. Also notice that the electron is not created or destroyed, it is just transferred. That's what electrovalent compounds are all about.

Well....Sort of right. In fact a very small number of the water molecules are actually ions.

Now don't get all upset. Only a very small number of water molecules are ionized. In rain water only one molecule in about ten million is ionic, the rest are covalent.

Yes, it is. But you can understand it.
Most water molecules are bonded together by the sharing of electrons (covalent bonds). But a small number of hydrogens lose in the tug-of-war, getting their electron stripped away by the oxygen. Those few molecules are electrovalent compounds. We will spend a lot of time talking about those exceptional water molecules in Advanced Alchemy. For now all I want you to know is that water is a covalent molecule most of the time. But a few rare water molecules are electrovalent. I'm sure you can live with that, for now.

Yes. Let's move on to another very common compound. Salt.

That's exactly what I mean. Table salt is an electrovalent compound. A proper Alchemist would call it sodium chloride, or simple "NaCl". The "Na" stands for sodium and the "Cl" for chloride.

Because that's sulfur. With a hundred elements and only 26 letters in the alphabet, you end up making some abbreviations that don't make much sense. I don't know why they didn't just abbreviate sodium as "So".

Yes, maybe so.

So... let's get on with the lesson shall we? Sodium (Na) has an atomic number of 11......

Into the next larger shell.

Yes. As the atoms get bigger we add on more shells to accommodate their electrons and move up the alphabet as we name each new shell.
Sodium is the first element in our lesson with an M-shell. The M-shell can hold 8 electrons (like the L-shell).

That's right. The M-shell will not put electrons into its d orbitals until it has filled the s orbital in the N-shell. But we are getting ahead of ourselves here. Sodium doesn't have an N-shell.

That's right. And if it were in the company of a very electronegative element (atom) like fluorine, it would have that single electron stolen away. Then it would form an electrovalent compound called sodium fluoride (NaF).
But we were talking about table salt, sodium chloride (NaCl). To figure out how it is bonded together, you need to know that chlorine (Cl) has an atomic number of 17.

Good. Now think about those electronegativities we talked about and how that would affect the way the sodium and the chlorine interact.

That's right.

That's right. The sodium ion (Na⁺) has the same electronic structure as neon.

Right. The sodium cation (Na⁺) is "happy" because it has a complete outer shell. Even though it has to lose a shell to do it.
Now, what about the chlorine?

That is very good reasoning. And that is exactly what it does.

Yes. That way, both the sodium and the chlorine have complete outer shells. The sodium loses one electron so it becomes a cation, with a charge of +1. Its outer shell is now a full L-shell.

Right. By accepting or donating electrons these two atoms complete their outer shells. The sodium cation (Na⁺) has the electronic configuration of the noble element neon (Ne). And the chlorine anion (Cl^-), with its complete M-shell, has the electronic configuration of the next largest noble element - argon (Ar).

Yes. Well done. You now know the two most common compounds in the ocean - water (H₂O) and table salt (NaCl). One of them, the water, is a covalent compound (for the most part) and the other one, the sodium chloride, is an ionic or electrovalent compound.

Good question. The salt is dissolved in the water. If you sprinkle salt into water it breaks up into the ions. Ocean water is H₂O with a bunch of ions, like Na⁺ and Cl^-. The water molecules get in the way of the two ions, so they cannot get together to form a proper compound.

Ah, well, yes you're right. I misspoke. And I'm glad you caught me. What I meant was you can get the compound NaCl from the sea.

Yes! Sort of. We precipitate it. By removing the water that keeps the ions apart, we allow the electrostatic forces to take over. The Na⁺ and Cl^- ions are able to attract each other and form the electrovalent compound NaCl. All you have to do is let the water evaporate. What you are left with are the salts.

Yes. And some other salts too.

Well, magnesium chloride for example. That's another ionic compound dissolved in sea water.

OK. Yes. Yes. you're right. I was wrong! Are you happy, now?

But you can make magnesium chloride salts from sea water by allowing the water to evaporate. Let's see if you understand electrovalent bonding well enough to explain magnesium chloride. All you need to know is that magnesium (Mg) has an atomic number of 12.

That's right. Now how would the electrovalent compound, magnesium chloride, form? (Once you take away the water.)

Not quit, but very close. Think about that magnesium cation. It has a +1 charge because it had one of its electrons stolen by the very electronegative chlorine atom. But what kind of shell does that magnesium have when it has lost only one electron?

That's right. Let's use a number with the superscript to help keep track of the total charge. That will be important with this compound. Mg⁺¹ still has an electron in its outer shell. Its outer shell is not compete. It is true what you said. The Mg⁺¹ cation is attracted to the Cl^-1 by the electrostatic forces. But the magnesium cation, with one electron missing, still has an incomplete shell. It has to get rid of another electron.

It sure can, with the help of another chlorine atom.

That's exactly what I mean. The magnesium atom gives up TWO electrons, one to each of two chlorine atoms. If that seems complex, let's try writing it out.
Mg -----> Mg⁺² + 2e^-
This means that the one atom of magnesium gives up two electrons, becoming a doubly positive cation.
Then 2Cl + 2e^- (from the magnesium) ----->2Cl^-1
and all get together to form the electrovalent compound MgCl₂.

Well, yes. But remember, that the bonds are different. What they have in common is that they will use any trick in the book to make a compound that satisfies Lewis' requirement that the outer shell be complete.

Oh yes. Plenty. I'll give you a few more examples at the end of this lesson for you to work on by yourself. But for now, tell me what you've learned about the formation of electrovalent compounds.

Yes, well put.
But I'd like to add an important point here. We have been talking about the atoms taking and giving away electrons to reach the electronic configuration of a noble element. That idea helps keep our thoughts straight. In fact, the electron an atom gains as it becomes an anion might come from a water molecule. On the other hand, when an atom loses an electron it might give it away to water. My point is that water can act as an "intermediate" in the electron transfer.

Don't get confused. It isn't that hard. All I'm saying is that the way we've been describing this gain or loss of electrons is a wee bit too simplified. It's very hard (perhaps impossible) to actually follow a single electron as it moves between atoms. It's easy to imagine but hard to actually see. Many ionic compounds dissolve in water because water can act as an "intermediate" in the electron transfer. Recall that water is a rather unusual molecule.

Yes. Please understand that it isn't like one molecule of water is different from another.
It is really a matter of statistics or populations of molecules.
A tiny drop of rain water may contain 100 million water molecules, and at any one time about 10 of them will be "ionized". But which 10 individual molecules is not important because each molecule changes from "ionized" to "un-ionised" and back again. All very quickly and without you even noticing it. Most of the time the oxygen and hydrogen atoms in the water molecule share their electrons. But every so often the oxygen atom gets a wee bit "grabby" and steals an electron away from a hydrogen. Then it is an ionic (electrovalent) molecule. And those two ions might float away from each other. That's the basis of a very important property of water that we will discuss in Advanced Alchemy, when we talk about acids and bases and something called pH (pronounced "pee-H").

Yes. However, the way we've described them is good enough for most Alchemists.

Do all bonds form in order to satisfy Lewis' law of complete outer electron shells?

All covalent and electrovalent bonds do. And I think that's what makes them more difficult for some folks to grasp. You have to keep thinking about shells and atomic numbers and such. But that's also what allows you to predict their behaviors. However, the third type of bond I want to teach you is much easier to understand. And it has nothing to do with water.

Well, metal (or metallic) bonds are the easiest, in my opinion.
You know of lots of metals; Iron (Fe), copper (Cu), lead (Pb), aluminum (Al), chromium (Cr), Zinc (Zn), and of course, silver (Ag) and gold (Au). There are some other metals too. But all of them behave much the same with regard to their bonding.

Yes. Don't bother trying to memorize them. You can always look them up later. Of course, it doesn't hurt to learn a few. Some are the abbreviations of the metals in other languages. For example, the French call silver and gold "argent" and "aurum". The Romans use to call iron "ferrum" and lead "plumbum" (because they spoke Latin).

You poor lad.
Anyway, all metals are very good conductors of electricity. That is a property of metals. All metals conduct electricity well, because they all use their electrons in a special way for making bonds.

Wait a minute. What do you mean they "conduct electricity"? I mean they allow electrons to pass through them easily. Here, I'll draw it. But I'm not going to draw all the electron shells. I'll just draw a circle to represent the entire atom and place its charge inside the sphere. In a metal, all the atoms are linked together by a co-operative sharing of electrons. Not just between a few atoms, but between ALL of them. Each atom contributes an electron or two which "float" throughout the material. These "wandering electrons" don't "belong" to any one atom. They "belong" to them all. Picture a piece of metal as a bunch of heavy cations in a cloud of free electrons. The electrons drift from one atom to another, attracted by the positive charges on the metal cations. But they never really stick around. Kind of like that cat in the village. He wanders around from house to house, looking for food. But he never stays around for long.

That's right! Nobody owns him because everybody owns him! But what happens when you put some food out?

Yes. And that is what happens with the outer electrons in metals. They wander around, attracted here and there, but not very willing to stick around. But if you give them a reason to move to a particular place, boy do they move! That's what an electric current is. Running cats! I mean running electrons!

Yes, you beat me to it! An electrical current is NOT static. It wouldn't be a "current" if it didn't move!
I don't want to get us too deeply into the physics of electrical currents. Let's just stick to the fact that a piece of metal is a bunch of heavy cations (the metal atoms that have lost a few electrons) in a cloud of free electrons.

Yes. That's an excellent way to look at it. The sharing is among billions of atoms, not just two. It is this "super sharing" that gives metals their special properties, like being so good at conducting electricity. Metals are also "malleable", that is, they can be hammered into shapes. And metals are "ductile", able to be drawn into wires. All these properties are shared by metals because they have similar electronic "structures"

All the atoms in a metal are cations. They all have lost a few electrons so they all have a positive charge. Because all the atoms (ions) have the same charge, they try to repel each other. This is the same electrostatic force we talked about earlier, but working in the opposite way. In electrostatics, not only do opposite charges attract, but same charges repel! So all these cations like to reply each other. That makes it easy to force the atoms to slip over one another in all directions.

Well, then they would lose the electrons they are "super sharing".

Right. But because they are "supersharing" they really aren't fully cations.

That's understandable.
One way to imagine a metal is that it is a bunch of atoms which are "almost" cations but are never completely cations because they have a sea of electrons around them to keep the charges to zero.

To keep it simple and illustrate how the electrons move around. It doesn't really matter.
You see, they are "partial cations" surrounded by electrons. If they were "complete cations" (like sodium ions, Na⁺), they would repel each other and seek negative ions (anions).

Right. So they aren't behaving live an electrovalent compound.

Yes, that's a good way to imagine it. We call that "glue" a "metal bond".

No. Most metals are solid (at comfortable temperatures like in this room). But not all of them. Mercury (Hg) is a liquid metal. Even at room temperature it flows like water. Mercury is still able to keep its electrons around. It doesn't fly apart. Later we will talk about solids and liquids and what makes them so. But for now I think you should remember that not all metals are solid.
Remember, all metals conduct electricity, and are malleable and ductile. Oh, and they all have a pretty "metallic luster".

Aye. That's what I said. But they shine only if they are pure metals. If they are rusty (contaminated) they don't shine.

Yes, they are (at least to the level of detail needed for us). Some Alchemists study the very fine details of electron positions and movement in metals. Those details are only important to the very advanced Alchemists working to create metals with special properties like super-conductivity and semi-conduction. Those are problems for a different century. But you have learned all one really needs to know about metallic bonds. What have you learned?

Any questions about metal bonds?

What do you think?

I think you've learned your Alchemy well!
You're right. Metals "supershare" their electrons as they attempt to have a complete outer shell.
But, a wee warning (just in case you wonder about it later).
Some metals "supershare" to produce an outer shell of eight electrons like we have discussed. But other metals end up with an outer shell of d or f orbitals!

Don't worry about the details. As you will learn when we talk about metals in the section EARTH, some metals "supershare" to create outer shells made of s and p orbitals (like we've discussed all before). Some other metals create outer shells of d and f orbitals, when they give up their few outer most electrons. There's not all that much to learn about those metals except that they sometimes give up an extra electron more than they have to.

I agree.

If you want to continue choose the next hyperlink.

PRINCIPLES OF ALCHEMY WATER Part Two The weak "bonds" (or forces) dominate the way molecules interact. Weak interactions determine the states of matter. VSEPR theory explains the shape of covalent molecules. Other molecules use electrostatics to make their simple shapes.