Grade 9 Chemistry, Lesson 5 - Elements and the Structure of the Atom - Free Educational videos for Students in K-12

Grade 9 Chemistry, Lesson 5 - Elements and the Structure of the Atom - By Lumos Learning

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00:00	All right , welcome to Mr Lee Han teaches you
00:02	stuff . This is grade nine chemistry , lesson five
00:05	elements and the structure of the atom . So an
00:08	element is a substance that contains only one type of
00:11	atom . So here we have the periodic table of
00:13	elements . We've got around 118 elements here and for
00:18	each one of these elements . It contains a very
00:20	specific type of atom that is unique to that element
00:24	. And you'll know something's an element because elements cannot
00:27	be broken down through chemical means . So that means
00:30	if you put it in any sort of chemical reaction
00:32	, it doesn't matter what kind . That element will
00:34	never turn into another element or break down into something
00:38	else . It's always going to stay that element now
00:42	an atom is the smallest bit of an element you
00:45	can have . That is still that particular element .
00:47	And here's what I mean by that . If we
00:49	take an element , let's say gold . If we
00:52	take a bar of gold and we split it in
00:56	half , what we now have is two pieces of
00:59	gold . They're slightly smaller , so let's keep doing
01:02	that . Let's split it again and again and again
01:04	and again and again until we get smaller and smaller
01:07	and smaller pieces of gold . Eventually , you have
01:09	a piece of gold so small that you can see
01:12	the individual atoms that make it up . That's how
01:15	small it is . We keep splitting it more and
01:17	more and more and just picking up . One of
01:19	the pieces will eventually have a piece of gold .
01:23	That's only two atoms big Now . If we split
01:26	that in half , we end up with just one
01:29	atom of gold . Now the thing is , we
01:31	can't split that one atom of gold and still end
01:35	up with two pieces of gold , because this is
01:38	the point at which things stop being gold . So
01:41	this is an element . It's made up of protons
01:45	, neutrons , electrons . If we split this in
01:48	half , if it was possible to split this in
01:50	half , you wouldn't end up with gold anymore .
01:52	You'd end up with a big mess of subatomic particles
01:57	so it would no longer be an element . Or
01:59	maybe it would be two elements . Um , but
02:03	that's what an atom is . An atom is the
02:05	smallest bit of an element that you can get ,
02:10	so each atom has a nucleus and electrons in orbit
02:13	around it . So in my picture here , we've
02:14	got the nucleus at the center and we have these
02:17	electrons orbiting around the nucleus . Now I should warn
02:21	you , this picture is not to scale . If
02:23	I drew an atom this big on the screen ,
02:26	you would not be able to see the electrons because
02:28	they're so small . And you also wouldn't be able
02:30	to see the nucleus because it's so small . In
02:33	fact , the nucleus is extremely small compared to the
02:37	rest of the atom , so it's 1 100 1000th
02:40	the size . That means if we had a nucleus
02:43	about this big , which is around two centimeters across
02:48	the edge of the atom would be a kilometer away
02:52	in either direction . So this this atom would be
02:55	a kilometer or two kilometers across , so it would
02:58	be extremely large . Another way people like to explain
03:03	. This is if you had a nucleus the size
03:05	of a pea , the atom would be the size
03:08	of a football stadium . So and Adam is mostly
03:12	empty space . That's what we're trying to get out
03:14	here . Mostly empty space , the very little mass
03:17	that it has is concentrated mostly in the nucleus ,
03:21	so we should go through the subatomic particles . These
03:23	are all the bits that make up the atom .
03:26	There's three main subatomic particles and their protons and neutrons
03:30	and electrons , so the protons are positively charged particles
03:35	and they're in the nucleus . So those are the
03:38	green guys there . The neutrons also in the nucleus
03:42	, are neutral particles , so I'll just go those
03:46	and end and then the electrons . We've already pointed
03:49	those ones out . These are the negatively charged particles
03:52	that orbit the nucleus . Now a regular atom does
03:58	not have a charge , so it's not going to
04:01	be positively charged or negatively charged , which means that
04:05	the positively charged protons are going to equal the negatively
04:09	charged electrons . So in this case , we have
04:12	123456 seven electrons . So to balance that out ,
04:21	there must be seven protons . And incidentally , there's
04:24	seven neutrons in this case , too . But the
04:27	seven protons is the important part , so this atom
04:30	balances out because it has seven protons and it has
04:33	seven electrons , all right , the atomic number .
04:38	This will be very important when we get to the
04:40	periodic table this periodic table picture here just has the
04:44	atomic number on it . So on the top left
04:47	in the periodic table , there's usually an atomic number
04:49	there . Each element has its own atomic number ,
04:55	and the atomic number is the number of protons .
04:58	An atom of that element has . It's kind of
05:01	confusing . Why we just say atomic number equals number
05:05	of protons . So for any element , the atomic
05:07	number is the number of protons it has . If
05:12	two atoms have the same number of protons , they
05:14	are the same element . So what I'm saying here
05:17	is that and Adam or an element rather is defined
05:21	by the number of protons in an attic . So
05:26	if two atoms have the same number of protons ,
05:28	they must be the same element . If two items
05:31	have a different number of protons , then by definition
05:33	they are different elements . Well , look at relative
05:39	mass protons and neutrons are roughly the same mass ,
05:43	so we we basically consider them to have the same
05:45	mess . The electron , on the other hand ,
05:48	is about 1 2000 , the mass of a proton
05:51	or neutron . So if we look at our scale
05:53	again here and we have a proton on the left
05:56	. We would need around 2000 electrons on the other
05:58	side to balance it out . So that being said
06:03	, the mass of an atom can be considered to
06:05	just be the mass of the protons and neutrons added
06:07	together . Because the electron contributes so little of the
06:11	mass , you know there's no Adam that we know
06:14	of that has 2000 electrons . There's no way that
06:18	would be stable , so there's no way that it
06:20	can even amount to the massive just one neutron ,
06:23	so we just ignore it . So if we're looking
06:26	at atomic mass , protons and neutrons are given a
06:29	relative mass of one atomic mass unit , or Amu
06:33	, and we use this atomic mass unit instead of
06:37	using kilograms or grams , because then the numbers would
06:40	just be silly . For example , if we wanted
06:43	to measure what one neutron or one proton would weigh
06:47	, it would weigh decimal . 0000000000000 0000000000 167 g
07:00	So that's kind of silly number to work with .
07:03	So scientists just came up with a new unit of
07:05	measurement called the Atomic Mass Unit , which weighs as
07:08	much as a proton or a new trial . Because
07:13	electrons are so light they're given a massive zero .
07:17	We just consider them to have no mass , and
07:20	then the periodic table shows you the atomic mass and
07:24	the atomic mass is the number of protons , plus
07:26	the number of neutrons . So here we have a
07:31	box from the periodic table , and in this box
07:34	we have the atomic mass at the bottom and you
07:38	know it's the atomic mass because it would probably be
07:40	the biggest number in there because remember at the top
07:43	left there for oxygen . Here we have an atomic
07:46	number of eight . That's the number of protons .
07:49	So at the bottom we have the atomic mass ,
07:51	which is the protons plus the neutrons , and it's
07:54	got to be bigger than just the protons . So
07:57	we have eight protons , eight neutrons that gives us
08:01	an atomic mass of 16 for oxygen . That's it
08:05	for this video . So tune in for the next
08:07	video . The periodic table , part one

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