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  • - [Instructor] When we humans look

  • at the universe around us,

  • we're blown away by the complexity

  • and the diversity of all the things we see,

  • from the scale of things in the cosmos like stars.

  • This is a picture of our sun,

  • all the way down to a more human scale,

  • and all the way down to the microscopic scale.

  • This is a visualization of a coronavirus.

  • It seems like there's an infinite number

  • of things out there.

  • But an interesting question has always been,

  • are there some basic building blocks,

  • things, a smaller set, a finite set of things

  • that we can put together to make up all of this complexity?

  • Ancients thought about,

  • maybe it's fire, water, wind,

  • but now we know that there are things called elements,

  • and we have classified them

  • on the periodic table of elements.

  • And we know today of about 118 elements,

  • but we might discover more.

  • But what's mind blowing is all matter

  • that we know of in the universe is made up

  • of combinations of these elements.

  • Now, what's even more amazing is most

  • of what we experience in our everyday lives is made up

  • of an even smaller subset of these elements.

  • For example, almost 99% of the mass

  • on Earth is made up of these eight elements.

  • And if we look at ourselves,

  • if you were to stare at your hand or look in the mirror,

  • life, as we know it,

  • is made up of mainly these six elements:

  • hydrogen, carbon, nitrogen, oxygen, phosphorus, and sulfur.

  • Now, the earth and life is made up of other elements,

  • but it is amazing how much complexity

  • and how much can be made with combinations

  • of the things that we see in the periodic table of elements.

  • Now, the next question is, all right,

  • we can make things out of these elements,

  • but what if we were to keep cutting an element

  • or what if we were to keep cutting a substance down?

  • What is the smallest unit that still maintains

  • the properties of an element?

  • And that unit, you have probably heard the word,

  • is known as an atom,

  • and atoms can be further broken down.

  • In fact, an atom has a nucleus

  • and inside that nucleus,

  • it has subatomic particles known as protons

  • and neutrons in that nucleus.

  • And then you could imagine buzzing around,

  • and we're talking about very, very small scale,

  • and it's hard to pinpoint.

  • It's more of a probability where you might find these,

  • but buzzing around that nucleus, you have electrons,

  • and the protons have a positive charge,

  • the neutrons have a neutral charge,

  • and the electrons have a negative charge.

  • But everything we're talking about is made up

  • of combinations of these three fundamental particles,

  • and what's especially cool is

  • a given atom is mostly free space.

  • You have the dense nucleus

  • but then these atoms are just buzzing around

  • when mostly free space.

  • And what actually gives an atom the properties

  • of a specific element is the number

  • of protons we're dealing with.

  • So for example,

  • what makes an atom a hydrogen is it has one proton.

  • What makes an atom a chlorine is that it has 17 protons.

  • The number of electrons can change.

  • That will change its charge

  • and that might change how it interacts with other atoms,

  • but it still will be classified as a, for example, carbon,

  • regardless of how many electrons it has.

  • And similarly, the number

  • of neutrons don't affect its charge,

  • but it will affect the mass that we're dealing with.

  • But even if you change the number of neutrons

  • and you have the same number of protons,

  • you're still dealing,

  • if you say you have six protons,

  • no matter how many neutrons or electrons you have,

  • you're still dealing with carbon.

  • And it's really interesting to appreciate

  • just how small atoms are.

  • If you think about it just as a number,

  • the width of, let's say, a carbon atom,

  • and there are smaller atoms,

  • like a hydrogen atom or a helium atom,

  • but the width of a carbon atom is roughly one times 10

  • to the negative 10th meters.

  • Another way to think about it

  • and it depends on the context you're seeing the carbon,

  • but roughly speaking, if you took 10-billion carbons

  • and put them side by side, it would be about a meter wide.

  • Or if you wanna blow your mind even further,

  • if you had about 10-million carbons

  • and put them side by side, that would be about a millimeter.

  • So try to approximate a millimeter.

  • A millimeter, depending on the resolution of your screen,

  • might be something like that.

  • There would be 10-million carbons,

  • depending on how big you're looking at this video,

  • just in that space over there.

  • If that doesn't blow your mind enough,

  • another way to think about it is it's estimated

  • that there are more atoms in a grain of sand

  • than there are grains of sand

  • in all of the beaches on Earth.

  • And if that doesn't blow your mind,

  • roughly speaking, if you took an apple

  • and if you made the apple the size of the earth,

  • then an atom in that apple would be the size of an apple.

  • You can hear that again and process that.

  • If you took, or another way to think about it,

  • an atom of an apple is to the apple

  • as an apple is to all of Earth.

  • So atoms are tiny, tiny, tiny.

  • So I'm gonna leave you there.

  • That's enough mind blowing for one video.

  • And then in future videos, we'll discuss more in depth

  • about atoms and the subatomic particles that make them up,

  • and we'll talk more

  • about classifying the different types of matter.

- [Instructor] When we humans look

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Elements, atoms and subatomic particles | High school chemistry | Khan Academy

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    Lai Kimu に公開 2021 年 07 月 05 日
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