Periodic table, trends, and bonding
Groups of the Periodic Table Properties of alkali, alkaline earth and transition metals. Halogens and noble gases.
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- In the last video we talked about how every atom really
- wants to have eight-- let me write that down-- eight
- electrons in its outermost shell.
- This is kind of the most stable configuration that an
- electron can have. And given this fact that's been
- determined just by observing the world, really, we can
- start to figure out what's likely to happen in different
- groups of the periodic table.
- A group of a periodic table is just a column of
- the periodic table.
- Like this group, right here, and actually I'll start with
- this group, because it's got a special name.
- This group right here is called the noble gases.
- And what's common when you go down a group in
- the periodic table?
- What's common about a column in the periodic table?
- Well, in the last video we saw that every element in a column
- has the same number of valence electrons.
- Or it has the same number of electrons in
- its outermost shell.
- And we figured out what that was.
- This column, right here, which we learned were the alkali
- metals, this has one electron in its outermost shell.
- And I made that one caveat that hydrogen isn't
- necessarily considered an alkali metal.
- One, it's usually not in metal form.
- And it doesn't want to give away electrons as much as
- other metals do.
- When people talk about metal-like characteristics of
- an element, they're really talking about how likely it is
- to give away electron.
- We'll talk about other characteristics of a metal,
- especially the way that we perceive metals as being
- shiny, and maybe they conduct electricity, and see how that
- plays out in the periodic table.
- But anyway, back to what I was talking about.
- This column, right here, this is called the
- alkaline earth metals.
- So this is alkaline earth.
- These all have two atoms in its outermost shell.
- So remember, everyone wants to get to eight.
- If these guys wanted to get to eight by adding electrons,
- they would have a long way to go.
- This way, we would have to add seven electrons.
- They would have to add six electrons.
- And who are they going to take it from?
- Because these guys don't want to give away their electrons.
- They're so close to getting to eight.
- So it's much easier when you're on the left-hand side
- of the periodic table to give away electrons.
- In fact, when you only have one to give away-- especially
- in the case of elements other than hydrogen-- when you only
- have one to give away, it really wants to do that.
- And because of that, these elements right here are very
- seldom found in their elemental state.
- When I say elemental state, it means there's nothing but
- lithium there, there's nothing but sodium there, there's
- nothing but potassium there.
- They're very likely, if you find this, it's probably
- already reacted with something.
- Probably with something on this side of the periodic
- table, because this wants to give away something really
- bad, this wants to take something really bad.
- So the reaction will probably happen.
- These are still reactive.
- The alkaline earth metals are still reactive, but not as
- reactive as the alkali metals.
- And that's because these guys are really close to getting to
- the stable magic eight number.
- These guys are a little bit further away.
- So it takes a little bit more, I guess you could say, of a
- push for them to give away two.
- These guys only have to give away one.
- And then we learned that this has two in
- its outermost shell.
- And then all of these elements, which are called the
- transition metals, as you add electrons, they're just
- backfilling the previous shell's d subshell.
- Right?
- So their outermost shell still has two.
- It still has those.
- If this is the fourth period, all of these elements'
- outermost shell has 4s2.
- And these elements are just backfilling their 3d
- suborbital.
- Or their 3d subshell.
- These are 2's.
- So these all have two outermost electrons.
- So all of these, like the alkaline earth metals, need to
- lose two electrons in order to, quote-unquote, be happy.
- And the way I think about this, and this is really just
- a way-- and it maybe it bears out in physical reality-- is
- that these guys have kind of a deep bench of electrons.
- That if they are able to shed some of these valence
- electrons-- so if I write iron has two valence electrons like
- that-- even if they shed these electrons, they kind of have a
- reserve of electrons in the d subshell for
- the previous shell.
- So if it sheds its 4s2 electrons, it still has all
- those 3d electrons that have a high energy state that can
- maybe kind of replace them.
- And I'll use everything in quotation marks, because these
- are just ways for me to visualize things.
- And the reason why I make that point is because metals are
- just very giving with their electrons.
- And these guys react.
- They say, hey, take my electrons.
- These guys say, take these two electrons.
- And these guys, they start to say, especially as you fill
- the d subshell, I've got these two electrons, and not only do
- I have those two electrons, but I have more electrons
- where-- well almost where-- that came from.
- I have some in reserve in my d.
- And what happens in these transition metals, and it
- especially happens in the metals-- so these are the
- metals right here, and these don't follow just a group, but
- this is the metals, this color right here-- is that they have
- so many electrons to hand off, not only do they have these
- extra there, but they filled their d subshell, that they
- can kind of, especially when they're in elemental form, and
- when I say elemental form, this means that you just have
- a big block of aluminum.
- Aluminum hasn't reacted with anything like oxygen.
- It's just a bunch of aluminum.
- Right?
- When you have a bunch of aluminum, what happens is you
- have these metallic bonds where all of the aluminum
- atoms say, you know what, I have all these extra, I have
- definitely, in the case of aluminum, three electrons in
- my outermost shell.
- But I have all of these kind of backfilled electrons in my
- d suborbital.
- I'm just going to share them with the other aluminum atoms.
- So you create this sea of aluminum atoms. And they're
- attracted to each other.
- Or you create this sea of aluminum electrons.
- So you have a bunch of electrons sitting in between
- the atoms, and since the atoms kind of donated these
- electrons, they're attracted to them.
- Right?
- So the actual atoms-- so this would be an aluminum plus, and
- maybe we would have donated three electrons.
- But I'm not being exact here.
- I want to just give you the sense of how things work.
- And that's why metals conduct really well, because
- electricity is just a bunch of electrons moving, and in order
- to have electrons moving, you have to have surplus electrons
- lying around.
- So elements right around this area are really good
- conductors.
- In fact, silver is the best conductor.
- Silver, right here, is the best conductor on the planet.
- And the reason why that's not used for our wiring and copper
- is because copper is easier to find than silver.
- But silver is the best conductor.
- And the way I think about it is that these-- once you've
- filled an orbital, that orbital
- becomes somewhat stable.
- So all of these guys have filled their d orbital.
- While these guys, their d orbital is not filled.
- So they just have a lot of surplus electrons that are
- really good for conduction.
- Now, that's just an intuition.
- I haven't done the experiment to prove that.
- But it'll give you a sense of why things
- conduct and all of that.
- So these are the transition metals.
- These are actually considered the metals.
- But the reason why these are considered the transition
- metals is because they're filling the d-block.
- But transition metals kind of sound like not
- as good as a metal.
- But when I think of metals, iron is kind of the first
- metal I always think of.
- I definitely think of silver and copper and gold as metals.
- So to call them transition metals is a little not fair.
- I don't really consider aluminum more of a metal than,
- let's say, iron is.
- But in chemistry classification world, aluminum
- is more of a metal.
- These elements right here.
- And I know I dropped off come from kind of the group notion.
- But let me just actually write the valence electrons.
- So these all have three valence electrons.
- Four, five, six, seven.
- So these all have three electrons in
- its outermost shell.
- It still seems easier for them to give them away than to take
- them, but maybe now, in certain cases, there could be,
- especially in the case of, let's say, boron, there could
- be a situation where it maybe could gain five electrons,
- although that seems hard.
- It's much easier to give away three and that's why a lot of
- the, quote-unquote, official metals
- show up in this category.
- And as you can see, as you go down the periodic table you
- can kind of have metals that have more and
- more valence electrons.
- So for, let's say, lead.
- It's still a metal, even though it has
- four valence electrons.
- And that's because the atom is so big, its radius is so large
- that the outermost shell is so far away from the nucleus,
- that those electrons are easier to take off.
- So for example, as you go down, carbon, those electrons
- are very close to the nucleus.
- So they're very hard to take off.
- So carbon would probably more likely gain electrons from
- somebody else to get to eight.
- While these guys' valence electrons are so far away from
- the nucleus that they're more likely to kind of want to get
- rid of them to get to eight and get back to an electron
- configuration of, let's say, xenon.
- And you go and then these guys are the nonmetals.
- Right?
- They're likely to probably gain
- electrons in most reactions.
- And then this yellow category that I said was highly
- reactive, especially highly reactive with the alkali
- metals over here, these are called halogens.
- And you've probably heard the word before.
- Halogen lamps.
- That's no mistake there to call them halogen lamps.
- That's not a random choice of words.
- Maybe I'll do a video on halogen lamps in the future.
- And then finally, we're at the noble gases.
- What's interesting about the noble gases?
- Well they have eight electrons in their
- outermost shell, right?
- Except for helium.
- Helium has two, right?
- Helium's electron configuration is 1s2.
- But all of these other guys, this guy's electron
- configuration is 1s2.
- This is neon.
- 1s2, 2s2, 2p6.
- So he has eight electrons in his outermost shell.
- So he's happy.
- Argon, same thing.
- The outermost shell will look like 3s2, 3p6.
- Krypton will have in its outermost shell
- will be 3s2, 3p6.
- It will also have some 3d electrons around as it
- backfilled back here.
- But all of these have eight in its outermost shell, so
- they're happy.
- They have no incentive to react.
- They're kind of like, hey, all of you other elements, just,
- you know, you guys can do all that crazy reactions that
- you've got to do, but we're happy.
- And we don't want to give or take electrons.
- And because of that these guys are highly, highly unreactive.
- Very, very unreactive.
- And you know, back in the day, when they used to make these
- kind of zeppelins, these big blimps-- the Hindenburg is a
- famous example-- they used hydrogen.
- And obviously hydrogen is a pretty reactive substance.
- It's actually very combustible and that's why it blows up
- very fast. And that's why now, clowns or children's balloon
- manufacturers, they instead would prefer to use helium.
- Because helium is a noble gas and it's very unreactive.
- And it's very unlikely to explode at a
- child's birthday party.
- But anyway, I think I'm done now with this video.
- And in the next video we'll talk a little bit more about
- trends across the periodic table.
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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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