0:03 welcome to the first video for chapter
0:05 four section one on ionic bonding
0:07 uh the learning objective for this video
0:08 is to explain the formation of cations
0:10 anions and
0:13 ionic compounds before we jump into
0:14 the definitions of what exactly an ionic
0:16 bond is and
0:18 what it consists of essentially an ionic
0:21 compound is a compound that consists of
0:23 some ions that are held together through
0:24 an ionic bond
0:26 and the properties of ionic compounds
0:28 can actually tell us quite a lot about
0:31 the characteristics of that ionic bond so
0:31 so
0:33 properties of ionic compounds when we
0:35 think of ionic compounds a good example
0:36 of an ionic compound is sodium chloride
0:38 which is table salt
0:39 so if you're thinking about just a
0:41 generic ionic compounds you can think
0:42 about table salt to kind of get a sense
0:44 of what of what these things
0:46 are um so they tend to be very
0:48 crystalline they tend to exist in these
0:49 very well-defined uh
0:52 structures they're very rigid which
0:54 means they don't deform easily
0:56 uh they tend to be incredibly brittle so
0:57 if you try to deform them they will
0:59 shatter rather than deform
1:02 and they also have a very high melting
1:04 points and boiling points
1:06 and together these properties tell us
1:07 that an ionic bond is
1:12 very strong it uh
1:14 these ionic bonds hold the ions in place um
1:15 um
1:16 very strongly which gives us the high
1:18 melting point and high boiling point
1:20 it's very difficult takes a lot of energy
1:20 energy
1:24 to separate the particles also uh it
1:26 means that our ionic compounds are very rigid
1:26 rigid
1:28 they don't deform because of these
1:30 strong bonds and if you try to deform
1:31 them they
1:33 actually shatter due to these um strong
1:35 bonds and essentially it's easier to
1:36 shatter than to
1:39 deform them and they are also quite
1:40 crystalline um
1:42 because of the uh the way that they
1:44 combine into these
1:45 very well-defined crystal structures
1:47 with these very strong forces holding
1:49 those ions in place
1:50 they also tend to be very poor
1:52 conductors of electricity when they're
1:53 in their solid form
1:55 and again this is because there's no ion
1:56 movement uh
1:59 in the uh no ion movement there we go
2:02 when they're in their solid form if you dissolve
2:03 dissolve
2:06 or melt an ionic compound then they
2:08 become good conductors of electricity
2:09 uh and again that's because when you've
2:11 dissolved an ionic compound like sodium
2:12 chloride in water
2:14 you've allowed those ions to move around
2:16 freely in the water
2:18 and they can therefore conduct
2:20 electricity the movement of charged
2:21 particles is is what electricity really
2:24 is and same thing if you melt them
2:25 you've essentially disrupted this ionic bond
2:26 bond
2:29 but again that takes a lot of energy uh
2:30 if you have ever
2:33 seen molten sodium chloride you were in
2:35 very specific conditions
2:36 most people have never seen molten
2:39 sodium chloride it takes
2:40 i think it's around a thousand degrees
2:43 celsius to melt sodium chloride
2:44 and once you do that then they become
2:46 good conductors because those ions can
2:48 move around freely
2:49 all right the next thing we're going to
2:52 do is jump into some definitions
2:55 so um the definition of an ionic bond
2:58 is uh the electrostatic forces of
3:00 attraction between
3:03 oppositely charged ions so if you have a
3:04 positively charged ion
3:06 and you have a negatively charged ion
3:08 the force that holds them together
3:10 is is what we call the ionic bond and
3:12 it's an electrostatic force between this
3:15 positive charge and this negative charge
3:17 all right so um the next thing is the
3:19 definition of what these
3:21 charges are what we call them so we're
3:22 always going to call a positively charged
3:23 charged
3:29 ion a cation so this is a positively
3:32 charged ion
3:35 and an anion is a negatively charged ion
3:42 and the way that i remember this is that
3:45 um cation the t in cation looks like a
3:46 plus sign
3:47 so it's like there's a little plus held
3:49 inside the cation word so
3:55 uh also it's really important for us to
3:57 remember that ionic compounds
3:59 and um the ions that that make them up
4:00 have very different properties than
4:02 their neutral atoms
4:03 so this is an example so this is solid
4:06 sodium this is chlorine gas
4:10 which is a diatomic and this is table salt
4:15 sodium is a very soft metal it's uh
4:17 it it lives in family one in the people
4:19 table um
4:20 this is a chunk of metal that someone
4:22 has sort of squished down into a vial
4:24 you can cut it with a butter knife it's
4:26 it's really incredibly soft
4:29 the thing is that it it violently reacts
4:30 with water it will actually catch on
4:32 fire if you expose it to water
4:35 um so it's it's it's very
4:42 it's very reactive um
4:44 this liquid in this vial is actually
4:46 mineral oil so sodium is usually stored
4:48 under mineral oil to prevent
4:50 any water from getting in contact with
4:52 it uh because
4:54 it it just immediately catches on fire i
4:56 actually one of my professors
4:58 in um undergraduate my undergraduate
5:00 degree tells a story about uh
5:02 when he was working in a lab and someone
5:04 cut some sodium
5:06 on a piece of paper towel and then they
5:08 went and did their experiment but they
5:10 threw the paper towel away in a trash
5:11 can and that trash can caught on fire
5:14 and uh had caused the entire building to
5:15 be evacuated and that was just from the
5:17 traces of sodium left on a paper towel
5:20 so this is incredibly violent chlorine
5:22 gas is poisonous
5:24 it's really nasty stuff um you can see
5:26 this sort of yellowish it's it's really
5:27 nasty stuff
5:29 and then sodium chloride this is table
5:31 salt right this is yummy
5:34 right well it's i mean not straight but
5:35 you put on your food to make it taste
5:36 good right so compare that with this
5:38 poisonous chlorine gas
5:40 and the stuff that burns if it comes in
5:41 contact with
5:44 the water vapor in the atmosphere um
5:45 it's uh
5:47 yeah it's it's they the ions and this
5:49 and the ionic compounds have very
5:50 different properties
5:53 than the neutral elements
5:54 all right so now we're going to talk
5:56 about why ionic compounds form or
5:58 exactly how they form
5:59 and we're going to focus on binary
6:01 compounds which are just compounds that
6:04 consist of two elements
6:06 they tend to consist of a metal and a
6:07 non-metal um the
6:09 cation the positively charged guy is
6:10 generally the metal
6:13 and that is because it tends metals tend
6:14 to have
6:16 low ionization energies i'm going to
6:17 abbreviate that as low ie
6:21 ionization energies and that leads
6:25 to um the metals losing electrons
6:28 and becoming positively charged right
6:31 uh and they tend to react with nonmetals
6:34 and the nonmetals tend to become anions
6:36 because they have a high
6:39 electron affinity and i'm going to
6:41 abbreviate that as ea
6:42 and what that means is that they tend to
6:44 gain electrons
6:46 which means they become negatively
6:48 charged and hey
6:50 cation anion and these guys tend to react
6:51 react
6:54 to form an ionic compound
6:57 so um so that's what these guys tend to
6:59 be the next thing that we need to think
7:01 about is the ratio
7:03 in which they react and the key here is
7:05 that all ionic compounds are going to be
7:07 electrically neutral
7:08 think about sticking your finger in a
7:10 bowl of table salt you don't get shocked
7:13 it's electrically neutral um so that
7:13 actually gives us some
7:15 really helpful information either if we
7:18 have the ratio or we have the charges we
7:19 can figure out the other
7:21 so here i've given you the charges um
7:23 this is going to form aluminum oxide
7:26 and aluminum tends to form a three plus
7:27 cation oxygen
7:30 is uh forms a two plus or sorry two
7:32 minus anion oxide
7:33 and when these guys react we have to
7:35 react them in a ratio that is
7:36 electrically neutral
7:38 for example if we tried a one-to-one
7:39 ratio um
7:41 let's see if this works we have a plus
7:43 three and a minus two
7:46 this guy would have a plus one charge on
7:48 it but we know that doesn't work out
7:51 so we're going to try a different ratio
7:52 and you can fiddle around with this and
7:54 just keep trialing and erroring
7:56 but sometimes when you have a an even odd
7:57 odd
7:59 mismatch it's actually a lot easier to
8:01 just multiply them by each other
8:03 so the low the least common multiple of
8:04 three and two is going to be six
8:06 and hey that turns out that's going to
8:08 be the the charge so
8:10 uh we're going to wind up needing two aluminums
8:11 aluminums
8:14 and three oxygens to make aluminum oxide
8:15 and let me just show you the math for
8:18 that so we have two
8:21 aluminums that are three plus
8:24 so that's a plus six and then we have three
8:24 three
8:28 oxygens that are a two minus
8:31 so that's going to be minus six so when
8:32 we add these up together
8:35 that gets us to neutrally charged life
8:36 is good
8:38 so this is the ratio and you can kind of
8:39 see how if we
8:40 only had these ratios we could work
8:42 backwards to figure out the uh the
8:45 charges of our ions
8:46 all right so the last thing i'm going to
8:47 talk about in this video before i move
8:48 on to
8:52 part two is that the formula is
8:54 not a physical arrangement it's really
8:56 tempting to if we look at aluminum oxide
8:58 or if we take a simpler case and we look
9:00 at sodium chloride
9:02 it's really tempting to say oh well okay
9:03 so sodium chloride
9:05 it's a one-to-one so there must be an
9:07 atom of sodium and an atom of chlorine
9:09 or rather an ion and an ion right a
9:11 sodium ion and then a chloride ion
9:12 hanging out and then there's another
9:13 pair of them over here
9:17 this is not the case um in fact what's happening
9:17 happening
9:19 is that as we said these guys are
9:20 crystalline they arrange themselves in
9:22 these very strong
9:25 tightly held crystal structures and
9:27 exact how exactly how the ions pack
9:28 there's a few different ways that they
9:29 tend to pack
9:31 and it depends on some factors but
9:33 essentially what happens is each ion
9:36 is exerting what we call an isotropic
9:38 attractive force so isotropic just means
9:39 it goes out in all directions
9:41 um three-dimensional right so it's in
9:43 all directions in three-dimensional space
9:44 space
9:46 and it's attracting uh this is a
9:48 negatively charged guy this is our anion
9:48 the chloride
9:51 is attracting the cation here the sodium
9:52 to it
9:54 uh in all directions and this turns out
9:56 to be the most stable form
9:59 um this uh this sort of cubic lattice is our
10:00 our
10:01 is our the most stable form for this
10:04 particular substance
10:06 this goes on for a really long ways
10:08 right this this is not just
10:09 nine atoms by nine atoms if you're
10:11 looking or nine ions by
10:13 nine ions if you're looking at a grain
10:14 of table salt
10:16 um you're probably looking at hundreds
10:18 of thousands or millions of atoms
10:21 on one side of your grain of salt um
10:21 remember how
10:24 infinitesimally tiny atoms are and ions
10:25 are um
10:28 uh anions tend to be slightly larger and
10:30 cations tend to be slightly smaller
10:32 um but they're you know comparable sizes
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