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hi kiddos welcome aboard for part two of
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subatomic particles we're gonna talk to
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in this video a little bit about
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isotopes and ions so we're we're still
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talking about our protons neutrons and
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electrons but in a couple of different
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ways to show that they're not always
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exactly the same as they were in
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Dalton's theory that Dalton's original
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atomic theory so remember we mentioned
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in the last video that this top number
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is the atomic number that's the number
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of protons that is essentially the
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defining characteristic of an element if
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it has six protons it is a carbon if it
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has eight protons it would be an oxygen
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so that number of protons becomes the
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defining characteristic you cannot under
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any circumstances change the number of
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protons and still have it be the same
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element however that's not true for
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electrons and neutrons and that's we're
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going to talk about in this video so
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we're to start off talking about
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isotopes isotopes are atoms of the same
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that are this of the same element so two
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carbon atoms but that they have
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different numbers of neutrons meaning
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that they're gonna have different masses
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okay so what would that mean well I
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would denote that by doing us a
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particular something called isotope
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notation so I would write the symbol of
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the element I'm gonna write to them
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because I don't have two different
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isotopes and then in the upper left
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okay so upper left above it so not like
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an exponent on this side
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but like an exponent on the opposite
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side of the symbol I would write the
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mass of that atom so in this case I'm
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gonna put 12 and again that would be an
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atomic mass units and for this one I'm
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gonna write another common isotope of
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carbon which is carbon 14 now if we're
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being technical you could also write
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down at the bottom the atomic number
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that's also pretty common to write for
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these it's not strictly speaking
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necessary because by the fact that by
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the measure of the fact that it's carbon
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it has to have an atomic number of six
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if it had a different atomic number then
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it wouldn't be carbon and so I don't
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really have to write that bottom number
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but what I do have to write is that top
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number that top number is the mass
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number if you remember from the last
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video what we said mass number
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is mass number okay and this also is a
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mass number that the mass number is the
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number of protons plus the number of
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neutrons and so what you can immediately
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tell here is that these two things have
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different masses and different numbers
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of neutrons this carbon is going to have
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six neutrons because it has six protons
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and six neutrons plus six protons gives
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me a mass number of 12 for carbon for a
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carbon 14 it's going to have eight
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neutrons because it's mass number is 14
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the easiest way is if you write these in
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isotope notation if you need to know the
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number of neutrons real quick you just
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do a quick subtraction 12 minus 6 would
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give me six neutrons 14 minus 6 would
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give me eight neutrons so I'm gonna
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write each of those up there real quick
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so six neutrons and eight neutrons now
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here's the thing neutrons don't don't
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define nearly as much about an atom as
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protons and electrons do but they still
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have a little bit of effect and the fact
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that we have those eight neutrons in the
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middle is going to lead to a little bit
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of nuclear instability and so what
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that's going to mean is that carbon-14
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atom is going to be slightly radioactive
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and you've probably heard of carbon
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dating and we would do that by carbon 14
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which is the radioactive isotope of
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carbon and we'll talk a little bit more
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about that in a future video what's
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important here is that there are two
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isotopes of carbon one with the mass
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number of 12 one with 14 in fact there's
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an isotope of carbon with a mass number
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of 11 and one with 13 also what has
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changed between each of those isotopes
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well it's not the protons and in this
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case it's not the electrons it is the
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neutrons if we change the number of
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neutrons we change the mass and
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therefore we have different isotopes of
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that element they're still going to
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chemically behave pretty much the same
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way but they might have some differences
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in their radioactivity in their
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half-life and those sorts of things what
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I also want to tie that into is you'll
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note that if you look here that that
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this number that I said in the last one
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was not mass number so what is that
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number actually well let's talk about in
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fact let's talk about it for something
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other than carbon since we've seen a bit
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of carbon all right so we said that this
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was the atomic number that's the number
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of pro
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Tong's and in a neutral atom it's also
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the number of electrons we said that
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this number was not the mass number
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these numbers are mass numbers and again
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mass number protons plus neutrons so if
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you wanted to find neutrons you would
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take mass number minus the atomic number
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and that would give you your number of
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neutrons okay so that's kind of
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important so then what is this number
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that's on the periodic table we're going
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to use that these numbers on the
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periodic table tons of times so what are
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they really so here's what they are they
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are the average atomic mass or we often
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say that they are the atomic weight of
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an atom and so you might be look at that
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going well that's really weird I mean if
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the mass of the atom is essentially the
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protons plus the neutrons then how do I
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get all these weird decimal numbers
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because I remember those atomic mass
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units and they were pretty close to one
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at least that out to a couple of decimal
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places so how do I get this weird stuff
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here well here's the way it works is
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because the number on the periodic table
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is the average atomic mass and to find
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that we take each individual isotope of
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it we multiply that by its relative
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abundance in nature in other words if we
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if we pull a sample of it in nature how
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much of of chlorine which is what we're
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working with here how much of that
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chlorine is 35 and how much of that
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chlorine is 37 and then we could
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calculate that to get this number on the
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periodic table so I'm gonna show you
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that real quick here so how do we get to
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the average atomic mass well we take the
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mass of each of the isotopes now you'll
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note that the mass of the ISTEP isn't
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exactly the mass number there's a lot of
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stuff that goes into that there's some
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mine Stein theories in there and amass
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defect and all that stuff it's not going
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to come out to be exactly that number
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don't worry about that for now trust me
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that these are the actual atomic mass
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units for these isotopes so a chlorine
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35 has a mass of this a chlorine 37 has
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a mass of that we would multiply them by
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their abundance now what we would really
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need to do is okay so we're going to
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multiply those well we would really need
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to do is convert those percent
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abundances into relative abundance which
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would just mean moving the decimal place
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turning them back into a decimal you've
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done that a hundred times in math
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classes so be 0.75 7 8 point 2 4 2 2
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we've multiple areas out we get 2 2
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and then we would add those numbers and
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when we add them up we were gonna get
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that number that's on the periodic table
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for every atomic weight on the periodic
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table every average atomic mass on the
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periodic table
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that's exactly how they're found we take
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many many samples of them we find out
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what different isotopes are in them
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what's the mass of each of those
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isotopes we find their abundance and we
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multiply them all together and you get
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this number so if you remember carbon
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had one of 12.0 107 if i'm not mistaken
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was its average atomic mass so what that
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would tell you is that the vast bulk of
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carbon hat is the mass of 12 which it is
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it's about 99% and then there's a little
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carbon 11 carbon 13 carbon 14 very small
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amounts but that gives us a mass an
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atomic weight that is slightly different
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than the 12 that is the most common in
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the case of chlorine you see that it's
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about a three to one ratio between those
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two isotopes and so that's gonna give us
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a mass that's closer to the 35 in but
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that that 37 still plays a pretty
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significant effect so that's isotopes
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isotopes again different mass numbers
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different numbers of neutrons let's talk
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a little bit of then about ions all
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right so what are ions ions and you
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probably already knew this but ions are
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essentially just charged atoms they have
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a positive charge they've got a negative
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charge a plus 2 a minus 3 whatever it
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doesn't have to be an atom it could be a
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group of atoms we'll talk about that a
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little bit later we'll talk about
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polyatomic ions but for the moment it's
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an atom that instead of being neutral
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has a charge and specifically the way
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that it gets a charge is that either
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gains or loses an electron if you
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remember well we've said for the past
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couple of videos you can't change the
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number of protons and still have it be
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the same element if you change number of
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protons that all bets are off that
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carbon is no longer a carbon it's now a
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nitrogen or a boron or something like
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that but what you can do is you can
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change the number of electrons and the
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atom is still fundamentally the same but
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it's now has a charge it's now an ion
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and so it's going to behave a little bit
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differently it's gonna allow it some
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different avenues for bonding and things
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like that so swiftly though I want to
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run through how that would actually
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happen
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so if we
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a sodium atom okay
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we look that up on the periodic table we
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see that it's atomic number is 11 which
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would in general indicate that there are
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11 protons K proton positive charge and
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generally that would also mean 11
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electrons but but sodium however being a
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metal and not a very electronegative one
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again we'll discuss that a little bit
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later it gives up its electrons pretty
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easily and so it's pretty likely the
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sodium has lost an electron okay
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and if sodium loses an electron then
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instead of it being balanced out between
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protons and electrons then what actually
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happens is I essentially have a full
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positive charge more because I have one
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more proton that I have electrons and so
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what that means is that I get a plus 1
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charge and so sodium in that case is no
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longer a sodium atom it is now a sodium
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ion that has a plus 1 charge how would
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that work in another direction well if
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we took something like say the chlorine
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that we were working on before we saw
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that that chlorine had 17 protons it's
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got an atomic number of 17 normally it
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would have 17 electrons also but very
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often that chlorine chlorine is pretty
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electronegative and so it's gonna gain
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an electron if we gain an electron over
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the 17 if we have one additional then
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again that doesn't balance out and
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become neutral instead we get a negative
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1 charge out of that and so that
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chlorine atom now becomes a chloride ion
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okay and so again gaining or losing an
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electron is what gives it a charge now
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one of the things that often confuses
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students is that losing an electron
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gives you a positive charge and gaining
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an electron gives you a negative charge
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Enfield's like like intuitively if you
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think about the words that that should
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work differently it feels like losing
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should make you negative and gaining
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should make you positive but remember
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that what you're losing or gaining is a
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negative okay so it has the opposite
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effect of what sort of like the normal
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English definition of that word would
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tell us and so that means that
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losing an electron makes something
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positive gaining an electron makes it
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negative and we're gonna talk a lot more
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about ions when we get into valence and
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electron configurations and all that but
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I thought you ought to know that along
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with isotopes while we were talking
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about subatomic particles
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all right thanks kiddos
