Name: Average atomic mass | Atomic structure and properties | AP Chemistry | Khan Academy
Uploaded: 2020-03-27T17:37:33.000Z
Duration: 8 min 38 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

- [Instructor] The thing that I've always found

In particular we're gonna be thinking about the atomic,

And by looking at that scale we can then begin to understand

and even be able to make predictions about what will happen,

and make things that are useful for human beings.

So if we're going to operate at this small of a scale,

and we're gonna appreciate in a few seconds

we're going to have to have some units of measurement.

And this video is going to focus on mass.

How do we measure mass at such a small scale?

has historically used something called an atomic mass unit.

I'll write it here, atomic, atomic mass unit,

that is denoted by just a U instead of an AMU.

Well, the unified atomic mass unit is defined as

Your first reaction, which would be an appropriate reaction,

is that wow, 10 to the negative 27 power is very small.

and then you would have one six six zero five four zero.

So very, very, very small, really unimaginably small.

We can only try to abstract it with things like mathematics.

is this feels like a bit of a hairy number here,

1.660540, why did they define it that way?

when we think about the mass of whether it's an atom

or the constituents of an atom like a proton or a neutron.

is approximately one unified atomic mass unit.

And the neutron is actually a little bit more

it's 1.008 approximately unified atomic mass units.

Now an electron's mass is actually far smaller

and usually neutrons and electrons as well,

on a periodic table of elements which we have here.

And we will study the periodic table of elements

But you can see a couple of interesting elements.

One, you have the abbreviation of a given element,

The number on top on this periodic table,

and that tells you how many protons it has.

And an element is defined by the number of protons.

So any atom that has exactly one proton in its nucleus

in its nucleus is going to be calcium by definition.

Any atom that has exactly 36 protons in its nucleus

So what would you expect the mass of a hydrogen atom to be?

that can have different numbers of neutrons.

actually has zero neutrons, zero neutrons.

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Average atomic mass | Atomic structure and properties | AP Chemistry | Khan Academy

entire

essentially

scale

average