Orbitals and Electrons
Valence Electrons Looking at valence electrons to figure out reactivity
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- So far, we've learned a little bit about determining electron
- configurations.
- Let's see if we can use that information to group elements
- on the periodic table and then guess as to what they might do
- when they react with other elements.
- So let's just figure out the electron configurations of a
- couple of elements just for a little bit of practice.
- So, lithium, right there.
- What does it look like?
- Lithium's electron configuration.
- You get the first shell, is 1s2.
- Two electrons there.
- And then you have 2s1.
- And sometimes, just to be quick, to get the notation, is
- you can imagine lithium's electron configuration is the
- exact same thing as helium's electron configuration-- this
- is helium's electron configuration-- plus the 2s1.
- This could have also been written as-- do that in light
- blue-- could also have been written as helium, 2s1.
- Which essentially means that lithium's electron
- configuration is exactly what you would have written for
- helium's electron configuration, and then you'd
- have written 2s1.
- You could do that a bunch of times.
- Let's say if we wanted to figure out the electron
- configuration of iron.
- Instead of going through the whole thing, you know, it's
- 1s2, and then it's 2s2, and 2p6.
- Instead of doing that whole thing, you could just say, OK,
- iron has the same electron configuration.
- So you could say iron's electron configuration is the
- same thing as argon's electron configuration.
- So I'll just put argon in brackets.
- And then you get 4s2.
- And then you have one, two, three, four, five, six.
- So d6.
- And we learned that when you're in the d subshell, or
- when you're in the d-block of the periodic table, you are
- actually backfilling the previous shell.
- So when we're in the fourth period, in the d-block, we're
- backfilling the third shell.
- So 3d6.
- And someone had asked-- and this is an interesting
- question-- why does it do that?
- Why does it not just continue?
- Why doesn't it fill the fourth d shell?
- And the way I think about it-- and this is all intuition, and
- things at the atomic level really start to become, on
- some levels, non-intuitive-- but the way I think about is
- as the atom grows larger and larger, there are more spaces
- between the previous orbitals.
- For example, this is just how I visualize it.
- If my first shell looks like this.
- Let's say the s looks like this.
- And then, if I just cut it out, let's say the p's look
- like something like this.
- This is maybe the second shell.
- The p's look like this.
- And then the next place an electron might want to be
- might be in the third shell, right?
- So the third shell would be like this.
- And then you fill out the third p shell.
- This is just an intuition.
- This isn't exactly what an electron would look like.
- Maybe the third p shell would look something like that.
- Look something like that.
- And then look something like that.
- And then you're in the fourth shell.
- So you're doing the fourth shell.
- The s subshell might look something like that.
- And then instead of immediately starting the next
- p shell, you're in the d-block now.
- So this is-- let me just write some labels-- 4s.
- This is 3s.
- This is 3p.
- This is 2p.
- This is 2s.
- And then 1s is inside of 2s.
- So you don't have to worry about that too much.
- But my intuition behind why the d orbital gets backfilled
- is because now, as the atom gets larger and larger, you
- have these spaces in between the previous orbital.
- So now, after filling the 4s subshell, or the 4s orbital--
- so this is 4s here-- out here, we go back and we fill in the
- 3d orbital.
- So we're going back and we're filling these
- spaces right here.
- So this is a lower energy state than this.
- It takes more energy to cram an electron back into the 3d
- shell, back there.
- But then once you do that, now you're ready to then go to the
- 4p shell, which might look something like this.
- So an electron would rather go to another shell, which is the
- fourth shell, rather than backfill the 3d shells.
- But once it fills out the fourth shell, it fills in
- those spaces in between.
- And as the electron gets bigger and bigger, there's
- more and more spaces in between.
- So eventually, when the electron gets big enough,
- there's going to be spaces between the d shells, and
- that's where the d orbitals and that's where the f
- orbitals will go.
- That's my intuition behind its working.
- And obviously, when we're dealing at the atomic scale,
- as far as I'm concerned, that's the best that I can do.
- But fair enough.
- That's not what I want to do here, but that was a good
- question, as to why do you go and backfill the third shell
- when we're in the fourth period?
- Fair enough.
- This is an easy way to write iron's electron configuration.
- The reason why I'm doing all of this is to figure out how
- many electrons you have in the outermost shell.
- In the case of lithium, you have one electron in your
- outermost shell, right?
- This is your outermost shell right here.
- You have one electron.
- And you could have done the same thing right there.
- In the case of iron, how many electrons in
- the outermost shell?
- Remember, the outermost shell is the period you're in.
- And this is the outermost shell.
- So even though these are higher energy electrons-- it
- took more energy to backfill those into the lower energy
- shell-- it's these that are on the outside energy shell, the
- fourth shell, that are going to be the
- ones that are reacting.
- And how many are there?
- There are two.
- And this is an important thing.
- So there's two here.
- There's two on the outside shell here.
- And actually, there's going to be two for any of these in
- pink right here.
- Any of the ones in the d-block, what happens?
- You fill whatever period you're in.
- Let's say that you're in period five here.
- Right?
- You're going to have 5s1.
- 5s2.
- And then you're going to go back and you're going to fill
- the 4d shell.
- Right?
- But in terms of how many electrons you have on the
- outside shell, in this case the fifth shell, you are going
- to have two electrons.
- So all of these are going to have two electrons in their
- outermost shell.
- In the case of these, the outermost electrons are going
- to be 4s2, right?
- Because then you go back and fill the 3d, but the outer
- ones are 4s2.
- So this one also has two electrons in
- its outermost shell.
- How many does this group have?
- And I've just used a word that I don't know if I've defined
- before, but the group are the columns in the periodic table.
- And as you can see, they all have patterns to them.
- Everything in this first group has one electron in its
- outermost shell.
- If you don't believe me, look at hydrogen.
- Hydrogen's electron configuration is 1s1.
- Its outermost shell is 1s.
- It has one electron there.
- Right?
- And that's true for all of these.
- All of these guys have two electrons in
- their outermost shell.
- These guys have those same two electrons.
- We can view it that way, in their outermost shell, but
- then they go and backfill the d shell.
- But in terms of their outermost
- shell, only two electrons.
- Than once you fill the d-block, or you go backfill,
- in the case of the fourth period, you go and backfill
- the third d sub-orbital.
- Then you go back to filling the fourth shell again.
- Now the p block, right?
- So this one's going to have three electrons
- in its outside orbital.
- Or you could say three valence electrons.
- This is four, five, six, seven, and eight.
- Let me do one more, just in case you don't believe me.
- What's the electron configuration for Sn.
- This is, what, selenium? [tin]
- I'm not even sure.
- But let's say Sn.
- What's the electron configuration?
- It's going to have the same electron
- configuration as krypton.
- Yes, that element is krypton.
- There is such an element.
- So it will have the same electron
- configuration as krypton.
- So I could have figured out krypton's electron
- configuration just by going through the whole periodic
- table, but this is just a faster way of doing it.
- Same thing as krypton, and then it has 5s2.
- Then it goes back and backfills the d-block.
- So then there's 10 there.
- So 4d10.
- And then it starts filling up the p-block in
- the fifth shell again.
- So 5p2.
- So how many valence electrons does it have?
- Valence electrons, or electrons in
- the outermost shell?
- Well, what's the outermost shell?
- It's the fifth shell.
- So these and these.
- These electrons have a higher energy state than that.
- It took a little bit more energy to cram them back into
- that previous shell than it took to put
- these on the s orbital.
- But if you talk about the electrons that will react, and
- that's why I'm emphasizing these, these are the electrons
- that are going to react with other atoms. Or sometimes with
- just other electrons, even.
- This one has four outside electrons.
- And you see that right there.
- Four outside electrons.
- And since the outside electrons, for the most part,
- are the ones that you're going to care about, there's a-- I
- guess you could say, a notation where you only draw
- the outermost electrons.
- So, let's say, for hydrogen, you could write it like this.
- Where you're only drawing the outermost, valence electrons.
- Valence electrons are just the outermost electrons.
- You could write it like that.
- You could write it like that.
- But this says, hey, I just have one outside
- electron for hydrogen.
- If I wanted to draw it for iron?
- Iron, right here?
- How would I do that?
- I have two electrons in my outermost shell, so iron I
- could just do like this.
- And electrons, they tend to be paired.
- So if I have, let's say I wanted to take the example of,
- if this is Sn, this is selenium.
- Let me do carbon.
- Carbon, I have four electrons in my outermost shell.
- So carbon I could write like this.
- Or if I didn't want to pair them, in theory I could write
- them like that as well.
- And now they're ready to react with other things.
- Now what does this tell me about, you know, this one has
- one electron in its outermost shell.
- These blue, these noble gases-- and we'll talk a
- little bit about them in a second-- have eight electrons
- in the outermost shell.
- How does that help me when I'm actually trying to figure out
- how things react?
- Well, it turns out that all atoms want to have eight
- electrons in their outermost shell.
- And that number is important.
- Eight.
- They want to have eight electrons in
- their outermost shell.
- This is the most stable configuration for atoms. Or I
- guess you could say, to some degree, a better energy state
- for the atom.
- And why is it the number eight?
- Well, that's something to think about.
- This is another fundamental number that
- just pops out of nature.
- And I've thought a little bit about it.
- It must be something about the atoms in the outermost shell,
- when you have eight, they resonate well with each other.
- And they somehow don't get in the way of each other.
- Or don't want to push away from each other.
- I don't know the answer to that.
- And frankly, if someone could really answer the question of
- why eight, exactly why eight, they would make a good career
- for themselves in physics or chemistry.
- But through experimentation, it has been well established
- that atoms want to have eight electrons in
- their outermost shell.
- So the question is, if you're dealing with something like,
- let's say you're dealing with potassium.
- Right?
- Potassium has one electron in its outermost shell.
- Let's say you have stuff like chlorine, that has seven
- electrons in its outermost shell.
- What do you think's going to happen if you put some
- potassium near some chlorine?
- What's going to happen?
- Well, what's the easiest way for the chlorine
- to get eight electrons?
- Well it has seven in its outermost shell.
- What's the easiest way?
- Well, it'll want to gain an electron really, really badly.
- And what's the easiest way for potassium to have eight
- electrons in its outermost shell?
- Well, if it lost that one electron, then it will have
- eight electrons in its outermost shell, right?
- Its outermost shell won't be the fourth shell anymore.
- It'll be the third shell.
- But it'll have eight electrons in the third shell.
- Its configuration will then look like argon if it loses
- that one electron.
- So it'll be a more stable state.
- So if you put sodium in the presence of chlorine, what's
- going to happen?
- This electron wants to jump off of sodium real bad so that
- sodium can have eight electrons in its outermost
- shell, or have an electron configuration like argon.
- And that electron is going to jump to chlorine, and then
- chlorine will have eight electrons in its outermost
- shell, and also have an electron
- configuration like argon.
- And so, as you can imagine, this group right here, which
- are called the alkali metals.
- And we'll talk probably in the next video why
- they're called metals.
- This group here, alkali metals.
- And they tend to exclude hydrogen, and
- we'll talk about that.
- These really want to give away electrons.
- And because of that, they're highly, highly reactive,
- especially if you put them in the presence of these
- elements, these yellow elements right here, which are
- called the halogens.
- These really, really want to take electrons from other
- things, because they just need one to get to eight.
- They usually want to give away electrons, because they just
- have to give away one to get to eight.
- And the reason why hydrogen, actually, isn't included is
- because hydrogen doesn't want to give away its electron as
- bad as these guys.
- This rule that your outermost shell wants to get to eight,
- that's true for everything except for
- hydrogen and helium.
- Hydrogen and helium, just because they have one shell,
- they're happy with just two electrons.
- And so with hydrogen, sure, it could lose an electron, but
- could just as easily gain an electron and be happy, because
- it'll have a full first shell.
- But all of these other ones, these alkali metals, they want
- to give away electrons really bad.
- When people in chemistry talk about metallic nature, they're
- really talking about how badly something wants
- to give away electrons.
- Anyway, I'm all out of time now.
- In the next video, we'll continue discussing the groups
- in the periodic tables and any trends we can
- ascertain from them.
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At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
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