Grade 9 Chemistry, Lesson 9 - Isotopes and Ions - Free Educational videos for Students in K-12

Grade 9 Chemistry, Lesson 9 - Isotopes and Ions - By Lumos Learning

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00:0-1	all right . This is Mr Lee Han teaches you
00:02	stuff . Grade nine , Chemistry lesson nine isotopes and
00:05	ions . All right , so why don't we start
00:08	off with isotopes now ? An isotope is an atom
00:10	with the wrong number of neutrons I put wrong in
00:13	quotation marks because there isn't really a right or wrong
00:16	here . It's just a helpful way to remember this
00:19	. Um , and here's what I mean , The
00:21	atomic mass of an element is not always a whole
00:25	number . So if you look on the periodic table
00:28	, you'll notice that the atomic mass is often a
00:30	decimal . Um , and this is because it's an
00:33	average of many isotopes of the element . So if
00:36	we take a look over here at the box with
00:39	chlorine in it , the atomic mass says 35 decimal
00:42	four or five . And the reason why is because
00:45	chlorine can potentially have either 18 , 19 or 20
00:49	neutrons . Um , and this would mean it would
00:52	have an atomic weight of either 35 36 or 37
00:58	. But you don't usually get a pure sample of
01:00	just one isotope of chlorine . So when you take
01:06	a sample of chlorine and it's all pure chlorine atoms
01:10	, you're gonna have a mixture of all those isotopes
01:14	. So if you actually way that sample , you
01:17	figure out the mass of that sample and then you
01:19	divide it by the number of atoms that would be
01:22	in that sample . You end up figuring out that
01:24	there are that each one weighs , on average ,
01:28	35 decimal , four or five atomic units , atomic
01:33	mass units . So that's why , uh , there
01:37	are decimal places in the atomic masses on the periodic
01:40	table . It's because of isotopes . Alright . Next
01:45	, we'll move on to ions , um , and
01:48	ions or atoms with the wrong number of electrons .
01:51	Once again , there's no right or wrong here .
01:53	But they are atoms with an unusual number of electrons
01:58	, right ? Not not the normal amount that you
02:00	would expect . So because they have either fewer or
02:05	too many electrons , they will have a charge of
02:08	some sort . As remember , electrons are negatively charged
02:12	, so if you take away a negative charge ,
02:15	they'll be positive , or , if you add a
02:17	negative , charges will be negative . So , for
02:20	example , oxygen at ions have a charge of two
02:24	minus , while lithium ions have a charge of one
02:27	plus noble gases . Noble gases do not form ions
02:33	. And the reason why is because noble gases have
02:35	a full valence shell . So their outer shell outer
02:40	orbit there has as many electrons as it can fit
02:45	, so they don't form ions . And the reason
02:47	why it's form ions to have a full valence shell
02:51	. That's the whole reason they do it . So
02:53	noble gases are already done . They don't need to
02:56	do anything . So elements will either gain or lose
03:00	electrons to have a full valence shell , just like
03:03	the noble gases . So if an element gains an
03:07	electron , it becomes negatively charged like chlorine . So
03:11	here we have chlorine , um , to have a
03:14	full valence shell . It needs to gain one electron
03:18	. And now , because it has more electrons than
03:20	protons , it's negatively charged . Um , if an
03:25	element loses an electron , it becomes positively charged like
03:28	potassium . So here's potassium , and it has that
03:32	one extra electron there and its valence shell . If
03:35	it gets rid of that , it'll be just like
03:37	argon , the noble gas . So it gets rid
03:41	of that , and now it has more protons and
03:44	electrons , so it is positively charged . So can
03:49	an element lose or gain a proton instead of an
03:52	electron to become an ion . The answer to that
03:55	is no most certainly not . Um , if the
04:00	number of protons changes , which it doesn't the data
04:04	, the atom would be a new element . So
04:07	, for example , we have flooring here . Florian
04:09	has an atomic number top left corner of nine .
04:14	If we added a proton to that , it becomes
04:19	neon . It's a totally different element . Remember that
04:22	elements are defined by the number of protons in the
04:26	nucleus , so you can't really change that . Um
04:31	, it doesn't make them an ion if you change
04:33	the number of protons . And really you don't change
04:35	the number of protons . Ah , in an atom
04:42	. Now , how do you know what charge and
04:43	ion would be ? Let's figure this out . So
04:46	what charge does lithium form ? So lithium here has
04:49	three electrons and it's got one in its valence shell
04:53	. The closest noble gas to lithium is helium .
04:58	So what do we need to do to make lithium
05:00	look like helium ? While we need to get rid
05:02	of this one Valence Electron and its valence shell .
05:07	If we do that , then it's just like the
05:10	noble gas helium . It has a full valence shell
05:13	because it's lost an electron , it becomes positively charged
05:18	. So lithium forms an ion with a charge of
05:21	one plus . Now , what charge does a flooring
05:25	ion Half . So Florian has 1234567 electrons in its
05:32	valence shell . So is it going to lose all
05:37	seven of those to be like helium ? Or is
05:40	it going to gain one to be like neon ?
05:43	Well , it's gonna be a heck of a lot
05:44	easier to gain one than it is going to be
05:46	to lose seven . So Florian gains one electron and
05:52	because it's got more electrons than protons now , it
05:54	has a negative charge . So Florian forms an ion
05:58	of one minus . Now what ? Charged as a
06:02	nitrogen ion half Well , nitrogen Scott 12345 And its
06:07	valence shell . So the closest noble gas to nitrogen
06:12	is neon . Um , so it's gonna be easier
06:15	to gain three electrons that will be to lose five
06:20	. So nitrogen gains three electrons and then gets a
06:25	charge of three minus , so nitrogen forms an ion
06:29	of three minus . Now , you may remember from
06:32	the last video that all the elements in a group
06:35	will have the same number of Valence electrons , and
06:38	because of this , they're all going to form ions
06:41	with the same charge . So here's the eye on
06:43	charges in the periodic table . The first column .
06:47	The first group gets charges of one plus second column
06:52	two plus , and we got three plus and then
06:57	right here we don't really give them charges in this
07:00	column . We've got carbon . It has four electrons
07:04	in its valence shell . So if it needs eight
07:07	to be stable , it's either going to have to
07:09	lose for or gain for . So it's kind of
07:13	in the middle , so it doesn't really form ,
07:15	and I on easily , so we just don't give
07:18	those charges . Now we're into the non metals and
07:24	these form negative charges . So now we have three
07:26	minus two minus and one minus . And then last
07:32	but not least , we have our noble gases which
07:36	do not form ions . So here we have the
07:41	periodic table , and this one has all the ion
07:45	charges on it . So on the top left Sorry
07:48	, top right corner . We have the eye on
07:50	charges , um , for all these elements , and
07:54	if you look closely , you'll see that some elements
07:57	show multiple charges . So all these highlighted yellow ones
08:03	. They have more than one ion charge Now .
08:07	These are called multi valent elements , and some metals
08:11	can form more than one stable ion . So if
08:15	we look at the box for copper , for example
08:18	, you'll see in the top right . You have
08:20	the , uh , I on charges that it can
08:22	form . It can form either two plus or one
08:25	plus . So copper can have a charge of one
08:31	plus or two plus , which means it can either
08:33	lose one electron or two electrons and become stable .
08:39	If we look at iron iron can form an ion
08:44	of three plus or two plus , which means iron
08:46	can become stable by either losing three electrons or losing
08:52	two electrons . So those are multi Valent elements .
08:59	Um , now it's important to notice that the 1st
09:01	20 elements I'll have only one stable ion . So
09:06	chances are if on a test you get an element
09:09	that isn't one of the 1st 20 Um , your
09:12	teachers put it there because it is a multi Valent
09:14	element , so that's that's a good thing to watch
09:16	out for on tests Polly Atomic ions , another type
09:20	of ion . Now , sometimes a group of atoms
09:24	can act like a single ion . So , for
09:27	example , carbonate carbonate is C 03 to minus .
09:32	Now , what that means is that the whole cocoa
09:35	three that carbon and those three oxygen all mixed together
09:40	. They all have a charge of two minus .
09:44	So that whole thing has one charge of two minus
09:46	that whole group . So that means that carbonate acts
09:49	similar to , um and Oxygen ion or a sulfur
09:54	ion , which are also to Maya's . Because this
09:59	poly atomic ion is negatively charged , it will react
10:03	with positively charged metal ions . And we'll get into
10:05	that in the next video . Um , but the
10:08	important part to remember here is that the whole group
10:10	of atoms behaves similar to just one single ion .
10:18	So another group is a hydroxide group which has a
10:21	charge of negative one or 11 minus , I guess
10:25	a sulfate group and a phosphate group . And if
10:30	you look at the names here except for the hydroxide
10:32	, you'll notice that everything ends with eight . Um
10:36	, that's a good thing to note . If you're
10:37	ever looking at something and it says carbonate or sulfate
10:40	or phosphate instead of falsified . Then you'll know that
10:44	you're probably dealing with a poly atomic ion . All
10:47	right , so that's it for this video tune into
10:50	the next video , Ionic Compounds , Part one .

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