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We humans have known for thousands of years,
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just looking at our environment around us,
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that there're different substances.
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These different substances...tend to have different properties.
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Not only do they have different properties;
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one might reflects light in a certain way, or not reflect light.
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Or be a certain color, or be have a certain temperature;
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be liquid, or gas or be a solid.
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But we also start to observe
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how they react with each other in certain circumstances.
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and here's pictures of some of these substances.
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This right here is carbon, and this is in the...in its graphite form
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This right here is lead; this right here is gold
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and all of the ones that I've drawn, that I've shown pictures of here,
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I got them all from this website right over there
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All of these are in their solid form, but we also know that we...
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It looks like there's certain types of air in it,
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certain types of air particles,
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and depending on what type of air particles you're looking at
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whether it is carbon, or oxygen, or nitrogen,
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that seems to have different types of properties.
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Or, there are some other things that can be liquid,
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or even if you raise the temperature high enough on these things.
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If you raise the temperature high enough on gold or lead,
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you could get a liquid.
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Or if you kind of -- if you burn this carbon,
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you can get it to a gaseous state,
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you can release it into the atmosphere,
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you can break its structure.
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So these are things that we've all kind of
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that humanity has observed for thousands of years.
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But that leads to a natural question
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that used to be a philosophical question,
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but now we can answer it a little bit better,
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and that question is, if you keep breaking down this carbon
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into smaller and smaller chunks,
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if there's some smallest chunk,
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some smallest unit of this stuff, of this substance
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that still has the properties of carbon?
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And if you were to somehow break that down even further,
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you would lose the properties of the carbon?
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And the answer is: there is.
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And so just to get our terminology,
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we call these different substances, that these pure substances
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that have these specific properties at certain temperatures,
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and react in certain ways,
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we call them elements.
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Carbon is an element. Lead is an element. Gold is an element.
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You might say that water is an element.
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And in history, people have referred to water as an element.
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But now we know that water is made up of more basic elements.
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It's made of oxygen and of hydrogen.
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And all of our elements are listed here
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in the periodic table of elements.
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C stands for carbon
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-- I'm just going through the ones
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that are very relevant to humanity --
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but over time you'll probably familiarize yourself with all of these.
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This is oxygen. This is nitrogen. This is silicon.
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This is -- Au is gold. This is lead.
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And that most basic unit of any of these elements is the atom.
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So if you were to keep digging in
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and keep taking smaller and smaller chunks of this.
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Eventually you would get to a carbon atom.
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Do the same thing over here,
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eventually you'd get to a gold atom.
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You did the same thing over here,
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eventually you'd get some of this little small
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-- for a lack of a better word -- particle,
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that you'd call a lead atom.
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And you wouldn't be able to break that down anymore
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and still call that lead,
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for it still have the properties of lead.
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And just to give you an idea
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-- this is really something that I have trouble imagining --
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is that atoms are unbelievably small.
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Really, unimaginably small.
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So for example, carbon.
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My hair is also made out of carbon.
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In fact most of me is made out of carbon.
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In fact most of all living things are made out of carbon.
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And so if you took my hair. And so my hair is carbon.
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My hair is mostly carbon.
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So if you took my hair right over here
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-- my hair isn't yellow
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but it contrasts nicely with the black.
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My hair is black. But if I did that,
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you wouldn't be able to see it on the screen.
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But if you took my hair here, I would have asked you
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how many carbon atoms wide is my hair?
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So if you took a cross-section of my hair, not the length,
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the width of my hair, and said:
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how many carbon atoms wide is that?
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And you might guess, oh, Sal already told me, it's very small,
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so maybe there's a thousand carbon atoms there,
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or ten thousand, or a hundred thousands,
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and I would say, no!
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There are one million carbon atoms.
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Or you could string one million carbon atoms
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across the width of the average human hair.
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And that's obviously an approximation,
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it's not exactly one million,
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but that gives you a sense of how small an atom is.
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You know, pluck a hair out of your head
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and just imagine putting a million things
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next to each other across the hair,
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not the length of the hair, the width of the hair.
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It's even hard to see the width of hair.
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And there would be a million carbon atoms
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just going along it.
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Now it would be pretty cool in and of itself
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-- we do know that
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there is this most basic building block of carbon,
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this most basic building block of any element.
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But what's even neater is that
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those basic building blocks are related to each other.
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A carbon atom is made of even more fundamental particles.
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A gold atom is made up of even more fundamental particles.
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And they are actually defined by
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the arrangement of those fundamental particles.
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And if you were to change
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the number of fundamental particles you have.
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You could change the properties of that element,
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how it would react,
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or you could even change the element itself.
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And just to understand it a little bit better.
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Let's talk about those fundamental elements.
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So you have the proton.
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And the proton is actually the defining
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-- the number of protons in the nucleus of an atom
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and I'll talk about the nucleus in a second --
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that is what defines the element.
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So this is what defines an element.
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When you look at the periodic table right here,
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they are actually written in order of atomic number,
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and the atomic number is
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literally just the number of protons in the element.
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So by definition, hydrogen has 1 proton.
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Helium has 2 protons. Carbon has 6 protons.
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You cannot have carbon with 7 protons.
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If you did, it would be nitrogen,
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It would not be carbon anymore.
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Oxygen has 8 protons.
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If somehow you were to add another proton to there,
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it wouldn't be oxygen anymore.
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It would be fluorine. So it defines the element.
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It defines the element.
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And the atomic number, the number of protons,
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the number of protons -- and remember,
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that's the number that's written right at the top here
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for each of these elements in the periodic table
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-- the number of protons
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is equal to the atomic number.
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Is equal to the atomic number.
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And they put that number up here because that is
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the defining characteristic of an element.
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The other two constituents of an atom
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-- I guess we could call it that way --
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are the electron and the neutron.
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And the model you can start to build in your head
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-- and this model, as we go through chemistry we'll see,
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it will get a little bit more abstract
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and really hard to conceptualize --
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but one way to think about it is
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you have the protons and the neutrons
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that are the center of the atom.
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They are the nucleus of the atom.
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So for example, carbon, we know, has 6 protons.
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So one, two, three, four, five, six.
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Carbon 12, which is a version of carbon,
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will also have 6 neutrons.
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You can have versions of carbon
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that have a different number of neutrons.
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So the neutrons can change, the electrons can change,
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you can still have the same element.
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The protons can't change.
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You change the protons, you got a different element.
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So let me draw a carbon 12 nucleus.
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So one, two, three, four, five, six.
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So this right here is the nucleus of carbon 12.
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And sometimes it will be written like this.
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And sometimes they will actually write
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the number of protons as well.
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And the reason why we write it carbon 12
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-- you know I counted out 6 neutrons --
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is that this is the total
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you could view this as the total number of
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-- one way to view it,
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and we'll get a little bit of nuance in the future
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-- is that this is the total number
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of protons and neutrons inside of its nucleus.
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And this carbon by definition has an atomic number of 6,
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but we can rewrite it here
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just so that we can remind ourselves.
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So at the center of the carbon atom we have this nucleus.
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And carbon 12 will have 6 protons and 6 neutrons.
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Another version of carbon, carbon 14, will still have
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6 protons, but then it would have 8 neutrons.
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So the number of neutrons can change,
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but this is carbon 12 right over here.
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And if carbon 12 is neutral --
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and I'll give a little nuance on this word in a second as well --
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if it's neutral it will also have 6 electrons.
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So let me draw those 6 electrons.
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One, two, three, four, five, six.
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And one way -- and this is maybe the first order way
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of thinking about the relationship
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between the electrons and the nucleus --
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is that you can imagine the electrons
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are kind of moving around,
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buzzing around this nucleus.
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One model is you could kind of
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thinking of them as orbiting around the nucleus,
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but that's not quite right.
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They don't orbit the way that a planet, say,
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orbits around the Sun.
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But that's a good starting point.
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Another way is that they kind of jumping around the nucleus
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or they are buzzing around the nucleus.
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And that's just because
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reality just gets very strange at this level,
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and we'll actually have to get to quantum physics
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to really understand what the electron is doing.
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But a first mental model in your head is
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at the center of this atom, of this carbon 12 atom,
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you have this nucleus.
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You have this nucleus right over there.
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And these electrons are jumping around this nucleus.
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And the reason why these electrons
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don't just go off away from this nucleus,
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why they are kind of bound to this nucleus,
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and they form part of this atom,
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is that protons have a positive charge,
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and electrons have a negative charge.
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And it's one of these properties of these fundamental particles.
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When you start thinking about
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what is a charge fundamentally other than a label,
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and it starts to get kind of deep.
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But the one thing that we know,
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when we talk about electro-magnetic force,
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is that unlike charges attract each other.
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So the best way to think about it is:
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protons and electrons,
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because they have different charges,
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they attract each other.
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Neutrons are neutral,
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so they're really just sitting here inside of the nucleus,
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and they do affect the properties on some level,
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for some atoms of certain elements.
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But the reason why we have the electrons
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not just flying off on their own
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is because they are attracted.
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They are attracted towards the nucleus.
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And they also have an unbelievably high velocity
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-- it's actually hard for --
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we start touching once again
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on a very strange part of physics
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once we start talking about
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what an electron actually is doing
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-- but is has enough --
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I guess you could say
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it's jumping around enough
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that it doesn't want to just fall into the nucleus,
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I guess is one way of thinking about it.
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And so, I mentioned carbon 12 right over here
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defined by the number or protons.
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Oxygen would be defined by having 8 protons.
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But once again, electrons can interact with other electrons.
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They can be taken away by other atoms.
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And that actually forms
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a lot of our understanding of chemistry.
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It's based on how many electrons an atom has,
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or a certain element has.
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And how those electrons are configured,
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and how the electrons of other elements are configured,
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or maybe other atoms of that same element.
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We can start to predict how an atom of one element
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can react with another atom of that same element,
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or an atom of one element -- how it could react,
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or how it could bond, or not bond, or be attracted to,
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or repel another atom of another element.
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So for example,
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and we'll learn a lot more about this in the future,
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is: it is possible for another atom some place
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to swipe away an electron from a carbon,
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just because for whatever reason --
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and we'll talk about certain neutral atoms of certain elements
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have a larger affinity for electrons than others.
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So one, maybe one of those,
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swipes an electron away from a carbon,
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and then this carbon will be
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having less electrons than protons,
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so then we'll have 5 electrons and 6 protons.
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And then we'd have a net positive charge.
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So in this carbon 12, the first version I did,
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I had 6 protons, 6 electrons, the charges canceled out.
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If I lose an electron, then I only have 5 of these,
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and then I would have a net positive charge.
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And we're going to talk a lot more
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about all of this throughout the chemistry playlist,
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but hopefully you have an appreciation that
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this is already starting to get really cool.
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We can already get to this fundamental building block
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called the atom.
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And what's even neater is that
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this fundamental building block is built of
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even more fundamental building blocks.
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And these things can all be swapped around
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to change the properties of an atom,
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or even go from an atom of one element
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to an atom of another element.
