0:03 isotope notation isotope notation is a
0:05 way that we can write the symbol for an
0:08 atom and show the number of protons
0:10 neutrons and sometimes electrons that
0:13 are in it isotope notation you see it
0:15 all over chemistry but it's particularly
0:18 important in nuclear chemistry because
0:19 in nuclear chemistry it's all about the
0:21 nucleus and so when when we write down
0:23 an atom we want to be able to show
0:25 pretty quickly how many protons and
0:27 neutrons are in it
0:30 so here is what it looks like to write
0:33 an atom in isotope notation we got a
0:35 couple things going on here first we got
0:38 these letters the letters represent the
0:40 element of the atom that we're dealing
0:42 with so here it's mg so we know which
0:44 stands for magnesium so we know we're
0:46 talking about an atom of magnesium then
0:48 we got these numbers
0:51 here the number down here is the atomic
0:54 number it's the number of protons that
0:56 are in the nucleus of this atom so here
0:58 we have 12 protons in the nucleus an
1:01 atomic number of 12 the number up here
1:03 is called the mass number which is the
1:05 number of protons plus the number of
1:08 neutrons don't make the mistake and
1:09 think that this is the number of
1:11 neutrons because it's not it's protons
1:14 plus neutrons together then we've got
1:17 two plus here and this represents the
1:20 net charge of this atom so we've got
1:23 protons and electrons and they balance
1:25 each other out so we have the same
1:27 number of protons and electrons have a
1:29 net charge of zero but unless we have
1:31 the exact number the exact same number
1:33 of protons and electrons the atom is
1:35 going to have a charge that's a little
1:37 bit negative or a little bit positive
1:38 and that's what the net charge
1:40 represents when we write something in
1:42 isotope notation it's usually because we
1:45 want to be able to find out the number
1:47 of protons neutrons and I said sometimes
1:48 electrons if you're adding the net
1:51 charge in here let's do this
1:54 now how many protons are in this atom
1:56 okay that's easy the atomic number here
2:01 is 12 so 12 protons how many neutrons in
2:03 this in this atom okay that's a little
2:04 bit harder because we don't have a
2:06 number here that's actually neutrons but
2:08 this number here is protons plus
2:11 neutrons together so if I know protons
2:13 and neutrons and I know the number of
2:17 just protons I can take my protons and
2:20 neutrons my mass number and subtract the
2:23 atomic number subtract the number of
2:26 protons and I get 25 minus
2:30 12 going to give me 13 neutrons the mass
2:33 number minus the atomic number okay
2:35 finally electrons here's how I like to
2:39 think about it this is a net charge of
2:41 positive so it means that we have to
2:44 have more protons than electrons and
2:46 since it's 2+ it means we have to have
2:50 two more protons than electrons okay so
2:53 if we had 12 electrons these guys would
2:57 balance out and they'd be neutral since
2:58 I need to have two more protons and
3:02 electrons I want to take the balanced
3:05 number of electrons minus two is going
3:08 to give me 10 electrons now I have two
3:10 more protons and electrons and that's
3:13 going to give me a plus two net
3:17 charge Let's do let's do another example
3:20 here let's swap
3:23 in titanium now you'll see something
3:25 right away about titanium and that's
3:27 that titanium doesn't have a net charge
3:30 written here and so if you write an atom
3:32 you see an atom written in isotope
3:34 notation and it doesn't have a net
3:36 charge that mean if it doesn't have a
3:37 net charge written up here that means a
3:39 net charge is zero the protons and
3:44 electrons balance perfectly so protons
3:46 neutrons and electrons for this guy
3:49 protons is the atomic number
3:55 22 and neutrons the mass number 48
3:58 protons plus neutrons minus 22 the
4:00 number of protons
4:03 and we get 26
4:06 neutrons for electrons they balance out
4:09 with protons and as we said since
4:11 there's nothing nothing up there it has
4:14 a zero net charge so that means I've got
4:18 22 protons and I've got 22 electrons
4:19 okay so now I want to go in the other
4:22 direction instead of taking a symbol and
4:24 finding out the number of protons
4:27 neutrons and electrons I want to start
4:29 with protons neutrons electrons I
4:30 already know how how many I have and I
4:35 want to write this symbol here okay so
4:37 let's start out with the atomic number
4:39 15 number of protons
4:43 okay I'll write that in right here now
4:44 how about the mass number well the mass
4:47 number is protons plus neutrons so I'll take
4:48 take
4:51 15 add it with 17 and I'm going to get
4:55 32 so that's the number that goes up
4:58 here 32 for the mass number okay what's
4:59 the letter that goes here what's a
5:02 chemical symbol well in order to find
5:04 that out I have to look on the periodic
5:07 table and I want to look for the element
5:10 that has an atomic number of 15 if I do
5:11 that I find out here that it's
5:14 phosphorus because I've got this 15 up
5:16 here so that means that any atom that
5:18 has 15 protons in it has an atomic
5:21 number of 15 it's phosphorus okay so I
5:24 put a big p here that stands for
5:26 phosphorous and now the net charge
5:28 what's going on here I've got my
5:31 electrons and I got my protons in this
5:33 example I have more electrons than I
5:36 have protons which means that my net
5:39 charge is going to be negative I've got
5:42 three more electrons and protons so that
5:45 means that the net charge is going to be
5:48 3 minus I kind of like to just figure it
5:50 out you know think about how many more
5:52 electrons or protons I have but if you
5:54 want to know how to always calculate the
5:57 net charge you can take the number of
5:59 protons and subtract the number of
6:03 electrons from it and there I get -3 and
6:04 that's my net charge we usually write
6:07 things 3 minus when we're doing the net
6:09 charge two minus you know that kind of
6:12 thing let's do another one of these okay
6:15 so what's the symbol of this going to be
6:17 it's always best to start with the
6:18 atomic number because that's really
6:21 straightforward 18 18 protons in the
6:24 nucleus now how about the mass number
6:28 I'm going to do protons plus neutrons 18
6:33 + 22 is going to give me 40 so the 40
6:36 goes up here how about the symbol the
6:38 symbol uh is dependent on this number
6:41 here 18 and look on the periodic table
6:43 to find out the atom that has an atomic
6:48 number of 18 and that's argon right here
6:51 so a is a symbol there how about the net
6:53 charge how do the protons and electrons
6:56 balance out it turns out that I have 18
6:59 protons and 18 electrons so they balance
7:01 out perfectly meaning that my net charge is
7:02 is
7:06 zero I just leave it blank I don't write
7:09 anything in there and that tells me that
7:12 I I don't have a net charge there okay
7:14 so that's how we can take an atom
7:16 written in isotope notation and figure
7:18 out the number of protons neutrons and
7:20 electrons that it has in it and then we
7:23 can also do the opposite we can take a
7:25 given number of protons neutrons and
7:27 electrons and go ahead and write the
7:30 symbol for it so that that is that's
