Calculating atomic weight | Chemistry | Khan AcademyYouTube↗  IA↗(long shot)
Education  327.4K views 753 likes 50 dislikes   13 Oct 2016
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- [Instructor] We have, listed here...
We know that carbon 12 is the most common isotope of carbon on Earth.
C12 (Kohlenstoff) ist das häufigste Isotop des Kohlenstoffs auf der Welt.
98.89% of the carbon on Earth in carbon 12.
98,89% des Kohlenstoffs der Erde ist C12.
And we know that, by definition, its mass is exactly 12 atomic mass units.
Definitionsgemäß wissen wir, dass seine Masse exakt 12 atomare Masseneinheiten umfasst (12u).
Now that's not the only isotope of carbon on Earth.
Das ist nicht das einzige Kohlenstoffisotop auf der Erde.
There are other isotopes. The next most frequent one is carbon 13.
Das nächst häufigste ist C13.
1.11% of the carbon on Earth is carbon 13.
1,11% des Kohlenstoffs der Erde ist C13.
And we can experimentally find that
Experimentell findet man heraus, dass
its mass is 13.0034 atomic mass units.
seine atomare Masse 13,0034u beträgt
So, these numbers that we have here, just as a review, these are atomic mass. These are atomic mass.
Diese Zahlen, die wir hier haben, geben die Atommasse eines Elements an
And so, what we're gonna think about, in this video, is how do they come up with the atomic weight number
Worüber wir in diesem Video sprechen wollen ist, wie die atomare Masse entwickelt wurde,
that they'll give you on a periodic table like that?
die im Periodensystem steht wie hier?
So, atomic weight. Where does that come from?
Atomgewicht. Woher kommt das?
Well, in the video on atomic weight and on atomic mass,
In dem Video zu Atomgewicht und Atommasse
we see that the atomic weight is the weighted average
sehen wir, dass das Atomgewicht der gewichtete Durchschnitt
of the atomic masses of the various isotopes of that element.
der Atommasse der verschiedenen Isotope dieses Elements ist
So, to find this roughly 12.01,
Um diese genäherten 12,01u zu erhalten,
we take the weighted average of these two things.
nimmt man den gewichteten Durchschnitt dieser zwei Stoffe
And what do we weight it by?
Wie gewichtet man das?
We weight it by how common that isotope actually is.
Man gewichtet es danach, wie häufig das Isotop vorkommt.
So, what we wanna do is,
Was wir machen werden ist:
we could take 98.89% and multiply it by 12.
Wir nehmen 98,89% und multiplizieren es mit 12.
And I'll rewrite this percentage as a decimal.
Ich werde die Prozentzahl als Dezimalzahl schreiben
So it'll be 0.9889 times 12.
Also 0,9889 mal 12
And, to that, we are going to add... We are going to add 1.11% times 13.0034.
Und dazu addieren wir 1,11% mal 13,0034.
So, as a decimal, that's going to be 0.011. That's 1.11% is 0.011, oh, 111.
Als Dezimalzahl wären das 0,0111.
And I'm gonna multiply that times 13.0034 atomic mass units.
Wir multiplitzieren 0,0111 mit 13,0034u.
So, what does that give us? Let's get our calculator out here.
Was ergibt das mit dem Taschenrechner?
So, we are going to have 0.9889 times 12 is equal to 11.8668.
Wir haben also 0,9889 x 12 = 11,8668
And, to that, we are going to add... We are going to add 0.0111 times 13.0034.
Und wir addieren mit 0,0111 x 13,0034.
And I know it's going to do this multiplication first because it's a calculator knows about order of operations.
Zuerst wird multipliziert, da der Taschenrechner die Rechenregeln kennt
And so, that's all going to be, as you can see, 12.01113774,
Und das ergibt 12,01113774
which, if you were to round to the hundredths place, is how this atomic weight was gotten.
Gerundet auf die zweite Nachkommastelle erhält man die 12,01 u
So that's that. There you go. That's how we calculate atomic weight.
So errechnet man das Atomgewicht.
So, I can write this as approximately 12.01.
Genähert also 12,01 u
It's the weighted average of the atomic masses.
Das ist der gewichtete Durchschnitt der Atommassen
Now, another thing that you might want to note is, what's the difference between carbon 12 and carbon 13?
Eine weitere Sache, die zu notieren ist, ist der Unterschied zwischen C12 und C13.
Carbon 12, this right over here, is six protons.
C12, das hier oben, hat 6 Protonen
The six protons are what make it carbon,
Die 6 Protonen machen den Kohlenstoff aus,
so both of these will have six protons.
weswegen beide 6 Protonen haben
And the difference is in the neutrons.
Der Unterschied liegt in den Neutronen
This right over here has six neutrons, six neutrons.
C12 hat 6 Neutronen
And this, right over here, is gonna have one more neutron, seven neutrons.
und C13 hat eins mehr also 7 Neutronen.
So, when you look at the difference in atomic mass, notice the change is...
Wenn man sich den Unterschied der Atommassen anschaut, erkennt man,
Looks like it's plus 1.0034 atomic mass units.
dass 1,0034 u hinzugekommen sind.
So, from this, you can say, "Hey, look,
So kann man sagen:
if I add a neutron... Plus one neutron.
wenn ich ein Neutron addiere
Plus one neutron. It's roughly equal to an atomic mass unit." It's not exactly an atomic mass unit, but, roughly speaking, in a lot of very broad,
Entspricht das ungefähr 1 u, nicht genau, aber gerundet kommt es 1 u sehr nahe.
high-level terms, you can kind of view it as being very close to one atomic mass unit.
And the same thing is true of protons.
Das trifft auch auf Protonen zu.
Anyway, hopefully you now have an appreciation for the difference between atomic mass, which is the mass,
Hoffentlich hast du jetzt eine Vorstellung von dem Unterschied der Atommassen,
and atomic weight, which is the weighted average of the various isotopes of that element on Earth,
die Masse und das Atomgewicht, welche der gewichtete Durchschnitt der verschiedenen Isotope der Elemente ist
how to calculate it,
und wie man es berechnet
and roughly what the mass of a neutron is.
und was die ungefähre Masse eines Neutrons ist, bekommen
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