The video provides a highly efficient synthesis of atomic theory and exam pragmatism, making it an essential resource for mastering MCAT chemistry. It successfully distills complex electron dynamics into actionable knowledge without sacrificing conceptual clarity.
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MCAT Chemistry High Yield: Understanding ElectronsAdded:
Hello everyone, welcome back. This is our lecture on electrons.
What are they?
>> What are electrons?
They're not protons.
>> They're not. They are fundamental subatomic particles that orbit the nucleus in probability densities known as orbitals.
They are negatively charged and nearly negligible in mass.
meaning that their mass is actually 12,000th of an amu from what I know. Someone look that up.
Good. My memory does not fail me.
This negative charge in the neutral state of the atom neutralizes the atom.
Believe it or not, because for a neutral atom in the ground state, you have the number of protons equal to the number of electrons.
The reason that the electrons don't I had this question asked the other day.
The reason that the electrons do not fall into the nucleus is what?
Why do the electrons not crash into the nucleus?
>> Opposite charges do what?
>> Attract.
In the same way that this is true that the gravitational force of attraction is GM1 M2 over R2 what is it F I forgot what it is I think whatever I don't care what it is f something K Q1 Q2 over R2 in the same way the gravitational attraction works.
Electrostatic attraction also works. So what I want you to imagine is that the nucleus is the sun and the electrons are the planets that they rotate around in an angular momentum in the same way that the planets orbit the sun and they don't crash in because their orbital momentum is kept in the same way every single time. How does that happen? Adam, God knows best.
>> Yes.
Is it the Heisenberg principle that you cannot look at the electron because if you look at it it moves but if it moves you don't look at it.
>> We'll talk about that in a second.
>> Let's talk about orbitals.
Orbitals are positions of electron density within sub levels. I always get this wrong of energy levels in the atom.
This is just a little bit of prerequisite knowledge that you would need before you come in to study for the MCAT. You need to know what energy levels are. You would probably need to know what sublevels are and you would probably need to know what orbitals are.
But just as a little bit of a review, if I have something like hydrogen and helium, lithium, burillium, boron, carbon, nitrogen, oxygen, florine, neon, uh what is this? Sodium. I forgot what's here. Is aluminum uh silicon.
Um is it calcium? I >> think so.
>> Calcium's too big. No. Isn't it magnesium?
>> It's magnesium, right?
Silicon, phosphorus, sulfur, chlorine, forgot what's after neon, doesn't matter. Bromine, iodine, that's good enough.
The way that we assort the periodic table is according to what?
>> Energy levels.
that we have energy levels at each and every single one of these periods. It's called the periodic table. We go by periods.
How do we assert these?
Huh?
>> Wrong.
By sublevel.
>> This is a suble and this is a suble. And when you have the D block, that's another suble.
The blocks are the sub levels. The periods are the energy levels and the orbitals can be inferred by the number of atoms within the suble. Meaning that when we have the first energy level, n equals 1, which is the first am I in frame?
>> You're writing it. n equals 1 which is the first period which contains hydrogen and helium. We see that there are two atoms there. The n= 1 only has how many sub levels inside of it? One.
And that would be the s suble with the 1 s orbital which carries two electrons. If you are confused, please watch our lecture on atomic structure.
Every time we go up an energy level, we add another what?
Sub level. Look at the Everyone pull up a periodic table. Everyone open a periodic table.
Looks something like that, right?
One, two, three.
Well, three would be like, "Okay, fine.
whatever at four. Every time we go up in energy level, we add another sub level.
Meaning that when we have energy level n equals 1, the sub levels that has access to is just s.
When we have energy level n equals 2, we have access to the s suble and the p suble. Then we have n= 3. We have access to the s, the p and the d suble. And when we have n equals 4, we have access to the spd f suble.
The filling of these orbitals within these sub levels is something that you must dedicate to memory.
Now we have 1 s2 which refers to helium because we go up to the nearest noble gas. Remember this is an guys if you're confused please go back atomic structure lecture.
This is an upper level chemistry lecture.
We have 2 s2 2p6. 2 s2 takes us where?
Look, takes you to the end of the suble.
Remember, cuz the s orbital, the s suble has how many orbitals? One. The p suble has how many orbitals?
Three. You go up by two every time. And the d suble has how many orbitals? Five.
1 2 3 4 5. Why? This is just the s orbital or this s suble. S orbital. This is px, p y, pz. Right. In the x, y, and z, z direction. Each of these orbitals carries how many electrons?
Huh? Two. So, doesn't it make sense that the p block, this is called the p block, has how many atoms inside of it?
It has to accommodate the number of electrons that the orbital can accommodate that the orbitals can accommodate that the suble can accommodate. How many is that?
>> Six. Because the p suble is made up of three orbitals which carry two electrons each making for six electrons. And those six electrons will correspond to one for every single atom inside of that group.
But don't forget why is the second energy levels period eight members long?
because of the fact that you had the 2 s2 orbitals, the 2 s2 orbital that was filled.
Are you guys lost? You guys get that?
>> So, when I look at the periodic table, especially because I want to do this before I move on to three because three is where it starts to get a little bit confusing.
Let's look at period two.
lithium, burillium, boron, carbon, nitrogen, oxygen, florine, neon.
This is on the left side. That's on the right. This refers to when we start filling things.
One second, guys.
I was just about to say what happened to me.
>> All right, >> this is how the periodic table is arranged.
These two elements right here, right, refer to what orbital?
This orbital. These six elements right here refer to what orbital? Wrong. They refer to the p suble and the p orbitals exist in that suble.
This p block refers to the six elements underneath the p sub the p suble which contains three p orbitals. And this s block refers to the two elements underneath the s suble which only contains one s orbital because the s suble doesn't have more than one orbital. Make sense?
We have energy levels which are split into sub levels and these sub levels are split into orbitals.
Yes, the s suble only accommodates one orbital. Every orbital accommodates two electrons. Thus, there are two atoms here. The p suble accommodates three orbitals. Each of those orbitals accommodates two electrons, which leads to six. Why is the entire energy level eight?
>> 2 plus 6. You fill the S, then you fill the P.
We get one S2, 2 S2, 2 P6, 3 S2, 3 P6.
Then what?
>> 4 S2 and 3d10.
This is where it starts to get funky.
that the 4s orbital or suble you can call it because there's only one actually has lower energy than the 3d and when we lose electrons we're actually not going to lose from 3d first we lose from four this fills first and is lost first so there can be an ion of something within the d block in the fourth period that has a plus2 energy uh a plus2 ionization or plus2 oxidation state.
What's something in the d block in the fourth period?
Copper.
Copper is in the D block in the fourth period. Copper is 3d what?
Believe it's five, right? Or is it seven? I don't know. Seven. 3d7. So copper is 1 s2 2 s2 2 p6 3 s2 3 p6 4 s2 3d7 that is copper neutral. If I wanted to make copper 2+ what would I do?
>> Remove the 4s2.
This actually comes up on the mcat all the time. This specific thing comes up on the MCAT all the time because they assume that you know that the 4S2 is filled because we're filling the 3D. But two of your answers are going to be 3D5 and 3d7. Pick the 3D7 that doesn't have the 4S2.
Make sense?
Huh? Okay.
Nine.
I don't have a period table in front of me. I thought I was just an idiot because I'm counting.
>> Is it just one before the end of the thing?
>> Yeah.
>> Okay, cool. Then that's nine.
>> What is seven?
>> Cobalt. Oh, yeah. That's why I remember it. Cobalt's weird. Cobalt's super weird.
>> You got that?
>> Okay. Let's ask a very, very simple question.
>> You saw the way >> alpha principle. Yeah.
Let's ask a very simple question which actually is not simple at all.
>> Yeah. Yeah. Yeah. Yeah. I asked if it was seven and you said yes.
>> I think you looked at cobalt and saw copper.
>> Let's ask a very simple question.
Since people are debating to come to my lecture or not should be able to answer that question very easily.
What is bonding?
Let's take 45 minutes to answer the question. No, you have a minute to answer this question.
>> No.
Do electrons have to be shared to bond?
No. Coordinate coalent bonding says they don't.
>> And two atoms create a compound.
>> Could be sometimes not. Could be an amalgamation. Could be an alloy or alloys bonds or amalgamations bonds >> or hydrates bonds? Do ions overlap?
What is bonding? Remember you have to account for coalent bonding, polar coalent bonding, non-polar coalent bonding, ionic bonding, coordinate coalent bonding, and everything else.
Yeah.
It's complicated.
Bonding is the use of fundamental and or simpler structures and molecules to build larger chemical complexes.
When in doubt, be vague.
What are the types of bonding I've taught you about? This is a very easy question to answer.
>> That's not a bond.
>> That is an intermolecular force.
>> Ionic.
Okay. 2 A and 2 B polar coalent non-polar coalent >> 2C coordinate coalent.
Anything else?
Not that you need to know about right now.
ionic define it.
>> Okay.
Metal non-metal mostly >> electron transfer from what to what?
more specific.
Low electro negativity to high with an electro negativity difference greater than or equal to 1.7.
Is it? No. You're right. You're right.
greater than 1.7.
Let's dive into when this becomes relevant for the MCAT. What are the most high yield and important places that ionic bonding comes up and what do the electron transfers mean within those specific scenarios within which we have ionic bonding?
Who can answer that question?
electrochem.
So, let's take a look at these one at a time. Actually, let's >> let's just blow up the whole board. Not like that.
Let's just blow up the whole board.
I want you to tell me what the electrochemical and electron ramifications are of ionic bonding as it relates to the MCAT.
First electrochem.
What do I need to know about this? And what do I need to know about electrons in electrochem?
Electrons do what? They move from blank to blank.
Electrons move from >> Are we sure?
>> Sometimes.
What do you mean depends?
>> Does it depend?
>> Can electrons flow from something that's being reduced into something that's being oxidized? Would that make sense?
What is a cathode and what is an anode?
>> Okay, so a cathode is where reduction occurs and an anode is where oxidation occurs. And if I have an anode and oxidation is occurring, that means electrons are exiting. Correct? Would electrons ever come back into the thing that's being oxidized? No. That'd be redundant. So, electrons flow from electrons flow from anode to cathode.
Why?
The reduction is happening at the cathode. Correct? And if the reduction is happening at the cathode, then this means that we have something to reduce with. What is the thing? We're reducing with the electrons from the anode.
All we're doing in the swapping from a galvanic to an electrolytic cell is we're flipping what's what.
In electrochem, the electrons move from anode to cathode. In a galvanic cell, the cathode is the part with the what?
The higher the lower reduction potential.
Cathode is where reduction takes place.
Galvvinic cells are what? Spontaneous or nspontaneous?
H spontaneous. So will what hap will we do what wants to happen or what doesn't want to happen?
>> We'll do what wants to happen. So what's happening to the cathode? It's getting reduced. And if the cathode wants to get reduced, then what's going to happen?
We're going to have a high reduction potential. That higher reduction potential indicates a a ability and a desire to be reduced over other things.
And that means that in a galvanic cell and put a G for galvanic cell. The cathode has a high energy potent uh reduction potential. Anode has a lower energy uh reduction potential and the electrons flow from here to here.
Flip that for not really flip that but flip these two.
In an electrolytic cell, the cathode will be the thing with the lower reduction potential. That's why we're putting energy into it. That's why we're pumping that thing full of electricity to make it act a way it doesn't want to act. Does that make sense? Because remember that the delta G is equal to the NF.
And the E of the cell is actually equal to what?
E what reduced minus E oxidized which means that it's delta G equals negative NF E cathode minus E anode and if the cathode has a lesser reduction potential than the anode this number is going to be negative making this positive making this non-spontaneous and that's why the electroic cell is nonspontaneous make sense question.
Another very simple but very hard question.
Why do some things have high reduction potential?
Why? Explain to me why. Why does oxygen have such a high reduction potential?
One of my students commented such something such a be so beautiful on my YouTube channel. He said, "It's not about memorizing. It's about understanding why."
Pat on the back.
Why?
Why? Why do certain things have This is not a rhetorical question. I want to know why.
It is a combination of high electron affinity and high effective nuclear charge loops back to periodicity like chapter one chapter two of general chemistry.
You need to understand this to understand the backbone of why reduction potentials are high or low in the first place and why certain things have higher or lower reduction potentials in the first place. Oxygen has such a high reduction potential because why? When it picks up electrons, it becomes so much closer to that octet.
It's why it's going to have a higher reduction potential than something like carbon.
Make sense?
Now, the thing is metals could really go any certain way. Metals are weird.
Metals are super weird in the way that they act, right? But really it's this the electron affinity has a lot to do with it. How much energy you're releasing when you take in electrons, right? And that amount of energy that's released is actually an amount of stabilization that's occurring. And that stabilization affects the reduction potential which affects the overall favorability of the reaction.
It's a stability thing. Make sense? Not to go too deep into that.
Where else is ionic bonding important?
What about enzymes?
H basic and acidic amino acid residues can compete and participate in acidbased reactions, specifically Bronstead acidbased reactions because of proton transfers.
And proton transfer is basically just oxygen taking positively charged hydrogen's and hydrogen's coming off of oxygen, leaving behind their electrons.
not truly ionic but you get the gist.
And some amino acids will actually be complex with certain metal atoms depending upon their negative charges.
This is important to the structure of the backbone of the enzyme.
Ionic bonding actually is a little bit important to what?
Salt formation.
And I say a little bit as a joke. It is the most important thing in salt formation which actually has implications on solubility which has implications from equilibrium which has uh implications from lhatier's principle which all has effects on kidney stones.
For some reason, the MCAT loves to talk about kidney stones, loves to talk about calcium oxalate and the way that it's going to solubilize inside of the urine after taking some sort of drug or whatever it may be. Just know that if anything hijacks Lhat Le's principle and starts using the common ion effect, now we're in some trouble because we can shift the equilibrium to a certain direction either to the formation of the solubilized product or the formation of the solid unsolubized product in which case you'll form the kidney stone.
Make sense?
It's not the chat leaders principle and the common ion effect are based in the same thing. It's just when is it being used? When is it being done?
Anything else? Ionic bonding going once done.
Coalent bonding has too many applications to talk about. So I want to talk about coordinate coalent bonding.
In order to perform a coordinate coalent bond, you need what?
You need two things.
Number one, you need a what do you need to form a bond corn bond?
You need a donor and an acceptor.
The donor is donating what?
An electron pair.
The acceptor is accepting an electron pair. Meaning it is electron deficient.
Doesn't this look an awful lot like something?
>> Lewis acid base theory.
So if you can identify Lewis acid bases, you can identify things that can be coordinate coalent bond donors and receivers. For example, it's a very classic example from chemistry. The reaction between I'm just going to draw it without the stereochem on this side.
Ammonia boron triloride coronav bond in biochemistry. What's the big coordinate cove of bond we talk about all the time?
Do you guys see how over here there's a p orbital that we're bonding into?
There's going to be a empty p orbital right here because we're not using up all four of those positions that boron can bond to because boron's happy with three for whatever reason. Don't ask.
It's one of those weird ones. That p orbital over there is what those electrons are coming into. So if we have an empty space that is electronegative remember p orbitals are electrogative like I said many times in my orgo lecture before right what's another thing that we can coordinate a coalent bond into if I can coordinate coalent bond into a p orbital I can probably co coordinate a coalent bond into a d orbital I can coordinate coalent bond into a d orbital anyone know what a hydrate is hydrate formation probably see it on the MCAT every now and again someone look up common metal hydrates on their laptop.
Someone read some of them off to me.
>> Not like that. No, no, no. Not Not those type of hydrates.
the water add like the addition of water to I forgot what they're called.
Hydration complexes, metal hydration complexes.
Let me see. I don't even know if I'm using the right name.
Yep, that's the one.
Oh, would you look at that? iron and cobalt and nickel and chromium. So, what's that water bonding to?
Iron and nickel and cobalt and chromium are all what?
Transition metals which have access to the d orbital.
So, what's happening is that this water molecule with its electrons are actually taking let's say something like iron, they're taking their electrons and binding into the open pocket of the d orbital because the d- orbital is a localized density of electron deficiency. If that d- orbital is not filled, then you have a problem. It is yearning for electrons. So that bond of the H2O's electrons into the d orbital allows us to understand that now d orbitals can be filled with electrons that are coming from nonionic species. This is what we learn from this that the d- orbital doesn't necessarily need to be filled with ionized electrons, electrons that fell off of other components, but they can be filled with electrons that are actually attached to coalent compounds.
Astounding. But what that does for us is that we realize that in the middle of the hemoglobin molecule when we have iron and it has its dorbital oxygen can hitch a ride on the iron.
Oxygen can coordinate coalent bond its electrons into the iron's d orbital to be carried throughout the bloodstream and dropped off when partial presses of oxygen are low. This is the methodology by which oxygen is carried throughout the bloodstream.
This is how it happens.
Have you guys heard Have you guys ever heard of chelating agents? Someone look up some famous chelating agents for me.
So coordin bonding, Lewis theory, hemoglobin, hydration complexes, >> or some famous chilating agents.
Uh this is a different note. Look at uh let's look at metal helicating agents.
Oh, but this is for like picking up metals itself.
Nah. All right. Whatever.
Culation is a big one here as well. Just take my word for it.
Unless you think I don't know what I'm talking about.
I might not on that keation point. I've actually never seen keelation done before. I've never had to administer chilation therapy. Thankfully, Good.
Let's continue.
Know what we're about to do?
and blow your mind.
Physics.
Let's take an atom, an atom X with a nucleus like that.
And I have atom X with electrons like this.
It's a helium atom. Let's say ah fine, helium, whatever.
I take this helium atom and I'm actually going to irradiate it with UV radiation.
And when this UV radiation hits the helium atom, it's going to strike this electron.
And as it strikes this electron, I can calculate the energy of this photon of light by what?
E equals HC over lambda or or never just write one, write both. HF.
Why? Because F lambda equals Guys, I do not know more physics than you do. Please f lambda equals C.
So f equals c over lambda and I can swap it in for that in this equation. What is h guys? What is this h? Huh?
>> What is it?
>> Planck's constant. Where h is plank's constant. 6.626 * 10 >> 34. Very good.
Where lambda is the wavelength in what?
>> No, in meters. Frequency is frequency in hertz one over seconds. And C is speed of light which is >> 3 * 10 the is it 8 or is it nine?
>> Eight. Eight what?
meters per second. Very good.
As you can see, I'm in a very bad mood today, which is why we decided to teach very, very basic, difficult to wrap your head around chemistry.
This is how I get my anger out by teaching chemistry.
Having a great day.
What's going to happen to that?
Two things are going to happen.
When this event happens and the electron is struck by the radiation, two things will happen. Number one, the electron will absorb what?
Yeah, it'll absorb energy from the light and become excited.
And this will lead to an electron transition.
And what that does is that it allows for the observation of the movement of that electron up to the next energy level.
Sorry, this is our OG electron.
This is our excited electron. And we denote that with what?
a star.
Number two, unabsorbed energy will be released and detected.
Meaning that if I take a look at this beam and the electron has absorbed that energy, what happens now is, tell me if this shows up on the camera, the pink. What happens now is that the rest of that energy is released out in a form of E equals E incoming minus E absorbed.
So, what can the MCAT ask you?
Well, actually before we do that, we need to we need to do one last thing.
This electron will eventually make its way back down to the ground state like that. And that will lead to the release of that energy that it once absorbed will come back down and I'll underline it this time so that it's grounded and what will happen actually is that we will get a release of energy from that electron that is actually exactly the amount of energy that it absorbs. So this is E abs.
I'm going to call this er e remaining.
Remember these are not actual denotions.
I'm using them for the example.
What can the MCAT ask you? They can ask you what is er.
They can ask you what is EABS?
How do we get these?
EABS is going to be calculated by what? They will give you either the frequency or the wavelength of this light.
And from there you will use the E= HC over lambda or HF equation to figure out the EABS.
Once you have the EABS, if you have the energy of the impending light, which you will probably have to calculate from a passage, you can subtract that from there to find the exact amount of energy that was left over that did not enter that did not enter. Because if you wanted to find in the impending right the impending if you wanted to find this all you had to do was move this over add EABS to ER. Does that make sense?
So what's happening is that the energy is scattering. The impending energy enters the impending photon of light.
Its energy enters the electron as much as it needs to go up the energy level.
It is contained within that electron and the rest of it bounces off. Boom. The part that bounces off we know that.
That's fine. In order to calculate how much came in, we need to know how much the electron is going to let go of when it drops down because that will be the exact amount that it absorbed in the first place. Make sense? You guys get that?
This right here, this photon of light right here, what is this when we look at it?
Normally on the MCAT, this is visible light.
Sometimes it's not, but this is usually visible light. When they ask you for it, that visible light, >> what color?
What color? They'll give you the wavelength of the frequency, they'll say, "What color?"
These are very high level questions because most people don't memorize those ranges. I didn't. And I, alhamdulillah, I got lucky. I got blessed.
But this is how emission spectra works.
When you have a little helium tube, a ray tube, and you turn on the switch when it's plugged into the wall, what's happening? You're putting energy into the helium. That energy is getting absorbed by the electrons. They go up to the excited state, fall back down to the ground state, and they release energy.
And that energy that's released is in the form of visible light waves. And those visible what? Light waves are visible through a spectr photoometer or whatever it's called. That little thing that you use in chem lab that you put up to your eyes and then looks silly.
You guys got that?
Huh?
>> Is it not the same thing to just say the opposite?
>> Yeah, I mean you could calculate you would calculate it from what's released.
The the impending photon doesn't need to be visible light.
Can you guys properly identify excited electrons?
Let's talk about it.
>> There you go.
Good man.
Excited or not?
Yes.
>> Set it. Adam of what?
>> Go figure it out.
I'll give you a hint that this is a neutral atom, not an ion.
Why?
>> Very good. Let's look at the three.
Let's look at the three block.
Lithium, burillium. Under lithium we have sodium and magnesium. That's our 3s2. Correct? Then we have on top we have boron, carbon, nitrogen, oxygen, florine. BCNOF easy. Aluminum is one.
silicon, phosphorus, sulfur, chlorine.
This right here is excited, meaning that in its ground state, it looks like 3 S2 3 P3.
So that would be an excited atom of phosphorus.
You guys see how to identify that?
Very good.
Make sense? You guys want to do another one?
You want to do another one?
What is X?
>> Is X2 plus?
What is X?
>> Tell me why.
I haven't counted it yet. That's why I stole >> it.
>> Very good.
Is it excited?
>> No, it's not.
>> It's nothing excited about this.
>> It's grounded.
Excited. grounded ion.
What is this?
>> It's probably not possible is what this is.
Most likely impossible. Why?
Yeah. Could you have something jump from 2p6 to like 3s or whatever it may be.
Are you gonna have two of them jump at the same time? Probably not.
More than likely not. This is the same thing as someone saying this.
I'm going to throw you guys back into this one real quick.
Possible or not?
Yeah, I like that face.
Possible.
Possible or not?
Who remembers their quantum structures and quantum numbers?
>> I suck at this.
>> What is n?
>> What is the n? What is n?
>> It is the energy level.
What is the domain of N?
One onward inclusive of whole integer values L. What is L?
>> The sub level which is inclusive of what?
>> N minus one onward whole integer values inclusive to what?
Actually the trick here is that you start at what?
That was the trick. You start at zero and you go up to n minus one.
That's the trick. Inclusive of whole integer values. ML. What's the domain here? These are the orbitals.
Oh, sorry. Z >> L to L inclusive whole integer values.
MS plus half negative half.
Give me one second.
Okay. So, is this possible or not?
Why not?
>> Yeah, because >> what's wrong?
>> The ML >> is outside of the bounds of the L. The first energy level only has access to the S orbital, which only has access to one suble. And I'm saying that this suble should be zero. Remember how we number suble? Let's take a look.
The first energy level has the s orbital which has one suble which gets numbered as zero and this is your positive 1/2 negative 1/2 electron. The second energy level has the s and the p orbitals. The s orbital has a single suble which gets numbered zero and we have a plus one to negative plus 1/2 negative 1/2. Then the p orbital has how many energy levels?
Three. 1 2 3. Take the middle one make it zero. What do we do next? This is your positive L and negative L.
positive 1 negative 1 because the p orbital is denoted as l= 1 and the s orbital is denoted as l equals 0 and then we have plus 1/2 negative 1/2 plus 1/2 negative 1/2 plus 1/2 - 1/2 make sense.
What about the d orbital?
L equals S was zero, P was one, D is two. How many sub How many sorry D suble? How many orbitals? 1 2 3 4 5. Where do I start?
The middle with >> zero and then I go >> 1gative -2 positive one positive two.
>> Um, sorry.
>> Ah, >> was it was it the oral that split two above, three below?
>> Got to get to that in just one second.
Sorry.
>> Up, down, up, down, up, down, up, down, up, down.
The d orbital is interesting. Doesn't really look like that.
looks like this with a very tiny minuscule infinite decimally tiny gap in energy which allows electrons of molecules in the d orbital to jump up and down within d within the d suble orbitals at will basically at room temperature and with no outside force and when they fall down they release what types of photons photons of visible light. And this is the reason that transition metals have color.
So when you see that a solution has color inside of it without any outside energy or force, when you dissolve it, you know that you have something that has access to the dorbital because only dorbital electrons are able to increase and decrease the energy at will with no outside force because of the very small gap between them. This is almost like having two tiny energy levels inside of this suble.
Make sense?
We'll cut the video here and do a part two. Thank you so much for watching. See you in the next one. Hello everyone.
Welcome back part two of electrons for the MCAT.
What role do electrons play in organic chemistry?
Everything.
Literally everything.
Electrons dictate what is a nucleophile or an electrophile because these are Louis acids and Louis bases. Correct? And from there you get carboation chemistry and ald doll chemistry and carbonial chemistry and alcohol chemistry and this and that whatever maybe blah blah blah all the five things that stabilize the conjugate base. All that is dependent upon electron dynamics. Correct? But the one big thing I really want to talk about when it comes to electrons and organic chemistry, what are we all thinking about?
Electrons, organic chemistry, we're talking about >> I guess since it's everything, it's a little harder to pinpoint. Resonance.
Electrons hate sitting still.
If they can move, they will.
Resonance is the deoization of electrons through a system of what?
Of conjugated what?
P orbitals, conjugated p orbitals because p orbitals are number one they are electrogative and number two they act like a wire through which the electron can flow.
What is the reason that we do resonance?
Not to find it, right? But you you said the word stable. What does that mean?
Why did you say the word stable? Because resonance is what?
>> It is a stabilizing it is a stabilizing maneuver that happens within the molecule. Correct? So this is a stabilizing maneuver that allows for what?
Dispersion and sharing of the electron density.
Now I have a whole lecture on resonance and you can look it up use a Hassan resonance lecture and it's an hour and 17 minutes or 20 minutes or something like that and I'm sure that you guys have seen it before. It's a very good lecture. I gave it two years ago and it's one of my favorite lectures to give because of the fact that resonance is so beautiful when you understand it properly. So let's look at a couple of examples of what resonance looks like, shall we?
As professor Molitzki used to always say, there is good resonance and then there is better resonance and then there is the best resonance.
Will that resonate?
Well, we have to see whether or not the p orbital system inside of this molecule is conjugated or not. Right? And in order to do that, we need to understand very well what a p orbital is, where it comes up, and why it would be in a molecule in the first place. And in order to understand that, we need to know a little bit about an H.
Hybridization. Sema, you're on a roll today. Why aren't you a little louder?
You give one wrong answer. Now you feel sad.
Wow. You guys would never make it make it in Professor Moy's class.
Professor called me a slur when I got an answer wrong >> in front of everyone.
>> Can you tell us what slur?
>> No, I it will get this video taken down off YouTube. And then after class when the camera was off, he called me another slur that was even worse.
That's my professor though. That's my guy. He's the reason I got a 521 on the MCAT. Maybe I should start calling Exactly.
>> I'm seeing a very strong correlation.
Second, you know, technical difficulties.
>> That's a long list though, >> huh?
>> That's a long list.
>> Figure it out. Hybridization.
What is the hybrid? What is hybridization? Hybridization is complicated. I never fully understood hybridization myself. But what you need to understand is that we have hybrid orbitals that appear between the bonding orbitals between two atoms when they combine. So when a carbon which is in the second energy level combines with hydrogen which in the first energy level, carbon is used going to use part of its p orbitals and its s orbitals to bond in with those hydrogen's. Correct?
And the hydrogen having only the s orbital is going to use its s orbital to do so. And what happens is that you get a merging of these hybrid of these orbitals that form hybrid orbitals that surround the actual structure. So let's take a look at carbon for a second. So carbon connected to four hydrogens's like this is actually going to have a structure something like this. It has one, two, three, four orbitals that are a mix of its one s orbital and three p orbitals that it is actively using actively using in order to bond. And the hydrogens's are going to bond in with their s orbitals here. Does that make sense? You guys understand that there's not much to understand, right?
Like I don't 100% understand this either. Hybridization is very difficult.
It's very complicated. Right?
Here's the thing. All those are being used because we see that this electron domain right here is being used to bond and this one right here and this one right here and this one right here. So we see that we have 1 2 3 four electron domains that are being used to bond. Correct?
Now what happens if less than four electron domains are used to bond. Well then we don't need to create that many hybrid orbitals. Right? Let's say that we have something almost like a carboation. And remember my last video from the VPR theory video. I can say that the carboation exists inside of a flat plane. This is going into the board out of the board and in the plane of the board sideways. So it's flat like this.
You guys see that? Let me draw it for you with my hand like this. This is my carboation. My arm is that and then my pinky is the one going into the board and my pointer finger is the one coming out of the board. Make sense? Which way is the p orbital going to go? Up and down perpendicular to the carboation.
Right. We're going to go up and down like this. Here's the thing. You might know that carboations have a p orbital just because I've said it so many times.
None of you guys questioned it. None of you guys said, "Oh, where did this p orbital come from?" Whatever it may be.
This is an untouched unhybridized p orbital. That's the thing. This is an unhybridized p orbital. Why? Because if I put a roup here and an RG groupoup here and an RG groupoup here, why did I put not put hydrogens's?
Primary pre-orbitals don't primary carboations don't exist. Can't put hydrogen's there, right? Or methyl carboations don't exist. Yes.
>> No, no, no, no. This is forget forget this for a moment.
>> We're looking at this, right?
This bond right here counts as one electron domain. This bond right here counts as another electron domain. And this bond right here counts as another electron domain. We have to talk about electron domains any single any bond basically a bond or a lone pair a bond single double triple right how many electron domains here three because if I draw this out in a dot structure it looks like in a line structure it looks like this three domains correct here's my trick for hybridization once again take your four orbitals.
Count off one, two, three. Cancel them.
How many got canceled here? An S and two P's, right? That means the hybridization is sp two. Drop the number of P orbitals right next to that P. What is this right here?
The lone P orbital right there. So something with an S sp2 hybridization is going to have a lone p orbital. Correct.
Very cool. What about something like this?
What about that? What about that carbon right there? That's a smiley face, by the way.
>> Like that's literally just a guy smiling on the molecule. It's not uranium.
>> Okay.
>> What is the the hybridization of this carbon right here?
How many electron domains does it have?
>> How many >> How many electron domains are on that carbon? This carbon right here. This one.
>> Four. There's four bonds.
>> But two of the bonds are in what?
>> A double bond.
>> So does a double bond count as one or two? Counts as one?
>> One, two, three. Let's do our little trick.
One, two, three. SP2 with a lone p orbital. That p orbital is being used for what?
the pi bond inside of the double bond.
That's where that pi bond is coming from. Now understood.
Now that we know the hybridization, we have to know what is a conjugated system.
What is a conjugated system? Huh?
Let's go back.
>> Abdullah, come here.
>> Come here.
>> Come here.
>> Wait, this is where you have the class.
>> Come.
>> Sit.
>> You have no students today, brother.
>> Sit.
>> I'm trying to sit. I said sit.
>> I said sit.
>> I have to leave.
>> Sit in the class.
>> I actually cannot. It's good to see you.
>> What is a conjugated system?
>> Oh, that's so simple. Give me that marker.
>> Am I on camera?
>> Yeah, you're on camera.
>> Okay. So, you know, conjugated, it means like alternating. You know what I'm saying? So, like if I have a double bond and then a single bond and then a double bond and then a single bond and then a double bond, that's a conjugated system because I kept switching.
>> See, Yousef likes to explain things with lots of rigor. You know, he likes to go in depth. But I'm more of like the kind of guy I am. I just want to get the grade and then get out of there. You know what I'm saying? I don't need like conceptual understanding. So, that's all you need to know. One big mistake to avoid which I actually made in a previous OEM quiz is the conjugated system start and end with the where the double bond is. So one time I had something like this and there was a double bond and I thought this conjugated system was three carbons long but it has to start and end with a double bond. So it can't start with a single bond. It can't end with a single bond. That's incorrect. That's correct.
>> Can I go back?
>> Oh, sorry.
A conjugated system is exactly what he said. But the reason for this, we'll >> talk about the coupling thing later.
>> The reason for this is actually quite interesting, right?
>> The reason for this is actually not just the double bonds, but it's anything with a p orbital inside of it. So, let's take a look for a moment. Let's say we had something like this.
I need you to very quickly be able to identify the hybridization of everything here. Everything. And if I look at it, I say everything's sp2 except for this guy. This is sp3. So is that guy going to be included inside of the conjugated system? Can't. Why not?
>> Doesn't have a p orbital. Doesn't have a p orbital. Right. The one thing that he said is incorrect is that the conjugate system starts and ends on a double bond.
What about this? Does that have a p orbital?
Does that have a p orbital? Do carboations have p orbitals? Yes, carboations have p orbitals in them.
Why? Because we have two bonds and we have a hydrogen. It's that implicit hydrogen that's not drawn. You guys aren't seeing it. That implicit hydrogen that's not drawn. Does this have a p orbital in it? Yes, it does. Okay, this does. What about this guy? Has a double bond. Has a p orbital. Double bond. P orbital. Double bond. P orbital. Double bond. P orbital. So, all of these guys are included in the conjugated system because you have a p orbital here and here and here and here and here. And when he said alternating alternating p orbitals across every single one of these things, because if you have stacked backto back double bonds, this is not a conjugate system. That's called a cumulated system. That's a cumulated system. Something completely different. I think they used to test that on the MCAT. Have you guys got a question about that recently? Got one question on a one project exam long time ago. I remember.
It talks about the rotation about the cumulated system where it's like the hydrogen's go here and then they go there and then they go here and then they go there. And this is complicated.
Not to mention that there's no hydrogen's in the middle of the cumulative system because all four bonds are taken up. But like you have to judge if the hydrogen's over here in this plane will the hydrogen at the end be in this plane or this plane. It's a very easy question to answer for all my OM people you probably remember that from your OKM lecture. Now we have conjugated system. We have an electron deficiency right here. Oh wow. That's not a conjugate system.
That's a conjugate system. We have conjugate system. We have electron deficiency right here. This is stable or unstable.
This is very unstable, right? We want to alleviate that by moving electrons around the p orbitals in order to get a new structure. And what that does is it allows for us to move that carboation around the molecule.
I see that.
And now everyone's kind of sharing the positive charge. Think of the positive charge as a 4,000 kg weight on the molecule. Would you rather have one measly carbon holding it up or four of them holding it up together? much easier, right? Much easier when there's multiple people doing the work that has to be done within the molecule. Make sense? Very good. This is how resonance works. And resonance works to lower the energy of the molecule. And this is why now we understand that with the lowering of the energy of the molecule, we are able to understand why the rate of an SN1 reaction is faster.
Uh let me give you a good example here.
Is faster for this guy than it is for this guy than it is for this guy. And it doesn't happen with anything less than that. Do you see why the SN1 reaction is going to be faster for this than for this than for this?
Because the SN1 reaction has a slow step. That's what the slow step of the SN1 reaction is defined by the transition state, which is a carboation.
and forming the carboation from these SN1 reactants is actually going to give us a good approximation of what we're going to see inside of the uh the vessel.
This is a tertiary carboation that cannot hydride shift because that's a secondary position. It's not going to hydride shift. This is a secondary carboation. They can't hydrate shift because that's a secondary position.
That's a primary position. It's not going to hydrate shift. But this this is a resonant carboation. And even though that's tertiary, it's still resonant which is going to take that. And if we were to do the resonance with this molecule, we would actually see, and I drew this this way very specifically, we would see that we're equally distributing this across two positions which look relatively the same. And now we have a 5050 split of that positive charge. So it's not really this. The actual molecule looks like what?
That's what the real molecule looks like. Isn't that beautiful?
Make sense?
>> Yes.
>> Say yes.
>> Where else do electrons come in the in organic chemistry?
Obviously have like nucleophiles, electro files. I've done so much of that stuff, man. Like we've we've done nucleophiles, electroiles into the grave, right?
Dang.
What is a reduction?
And what is an oxidation?
What is a reduction? What is an oxidation?
>> A loss.
>> Yeah. So, a reduction is a gaining of electrons and oxidation is a loss of electrons.
But I'm not really concerned about reductions like this.
That's electrochem.
That's electrochem.
I'm not worried about those types of reductions oxidations.
What I'm worried about is this.
What's that? Is that a reduction or oxidation?
What's this? Is this a reduction or an oxidation?
What's this? Is this a reduction or oxidation?
What's this?
That's what I'm worried about.
That's what I'm worried about. What is this?
This is what why where are the electrons? Where are these electrons you're talking about? What electrons is it gaining? Let's go all the way back to this.
What is this? Is this a reduction or is an oxidation?
Remember your alcohol chapter?
Alcohols blank into aldahhides.
Fill in the blank.
Alcohols oxidize into aldahhides. Meaning that this thing needs to lose electrons, right?
What electrons are we losing here? What are we talking about?
Watch very closely.
Watch the orgon magic. You'll never forget this. This is how biochemical reductions and oxidations work. I feel like I've done this before, but we'll do it one more time.
This is the only time I'm going to draw these implicit hydrogens right here.
I'm going to take an oxidizing agent called Ox plus.
That oxidizing agent is going to actually do what?
What it's going to do is it's going to take this hydrogen and its electrons, snag it away.
Right?
So now we've taken that hydrogen. Actually, nah, let me do this.
I'm going to say that everything I'm about to put on the board is theoretical. This is the theoretical method by which I understand oxidations of reductions. I want you to implement the same thing inside of your own practice so that you get used to seeing this. You can see everything disappearing. You have some oxidizing agent. Let's call it let's call it NAD.
Just for giggles, let's call it NAD.
Okay, NAD takes this hydrogen and its electrons gone. So, what it's actually doing is it's removing this hydrogen.
It's adding a hydrogen and its electrons right here and it's leaving behind a gap. Yes.
Make sense? So now NAD has become N a DH. Is there a charge? No. Minus and plus merge and become neutral. But now we left behind a charge right here. That charge can be easily fixed by what?
Folding down the electrons from this oxygen right here. And what happens is that these electrons leave from the hydrogen, drop down to make a double bond here. It fixes its orientation to a hydrogen. And now we have a lone H+ right here. And that H+ joins the NADH and makes NADH and H+. This is why I make such a big deal out of saying it's NADH and H+. If you just show NADH, you're not showing that final proton removal. Do you see how that's an aldahhide? What did we come from?
Do you see how this guy became this guy and this guy became this guy when we added NA+?
The loss of the electrons isn't happening from the molecule itself. It's happening from the hydrogen. We're taking the electrons of hydrogen running with them. Make sense? What is the original >> this >> ethanol? It's You're just not used to seeing it this way.
>> That's how you're used to seeing it. I took this and turned it on its head.
Professor Miski used to say that all the time. Taking this and turning on its head.
Used to go like that. Turning on its head.
He's a silly guy. He doesn't remember. I go into the flask.
No, you don't. You were never in the flask. He's like, I am looking at the molecule.
This guy was tripping, bro. Tripping out of his mind. The walls were melting.
I am in the flask. In the molecule. No, you're not. You were never in the flask of any molecule anywhere.
Okay, so that's how oxidations work.
Reductions are the exact same thing but backwards in the sense of let's say that I had a double bond right here and I wanted to take that double bond and turn it back into something that had electrons on it. What I'm going to do is I'm going to take FADH2.
And this is basically just F A DH minus plus H+. Let's just say for a moment that it looks like that for a moment.
Looks like that. What can happen here?
That H+ can pop open this double bond, drop itself right here.
Right? Look, H+ this double bond can swing open, grab that H+ that makes this this and a positive charge right here.
And then that H minus can occupy that spot right there. And that's going to give us so by doing that we've taken FADH2.
We've done that.
Why is that a reduction? We took the electrons from the hydrogen. We threw them on there along with another proton that was already there. Make sense?
Why? Where does this come into play?
What's that?
That's fummerate.
And if you were to do this backwards how you make FADH2 from complex 2 and suate dehydrogenase sumerate make sense very good you guys get oxidation reductions makes a little more sense Good.
Thank you guys so much for watching. I will see you in the next one. Take care.
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