And I've actually seen this drawn this way in some chemistry classes or physics classes, and my immediate question is how does this half know that it must turn into nitrogen? And how does this half know that it must stay as carbon? And the answer is they don't know. And it really shouldn't be drawn this way. So let me redraw it. So this is our original block of our carbon What happens over that 5, years is that, probabilistically, some of these guys just start turning into nitrogen randomly, at random points. So if you go back after a half-life, half of the atoms will now be nitrogen.

So now you have, after one half-life-- So let's ignore this.

File:Half-age-plus-seven-relationship-rule.svg

So we started with this. All 10 grams were carbon. This is after one half-life. And now we have five grams of c And we have five grams of nitrogen Let's think about what happens after another half-life. So if we go to another half-life, if we go another half-life from there, I had five grams of carbon So let me actually copy and paste this one. This is what I started with. Now after another half-life-- you can ignore all my little, actually let me erase some of this up here.

Let me clean it up a little bit. After one one half-life, what happens? Well I now am left with five grams of carbon And by the law of large numbers, half of them will have converted into nitrogen So we'll have even more conversion into nitrogen So now half of that five grams.

So now we're only left with 2. And how much nitrogen? Well we have another two and a half went to nitrogen. So now we have seven and a half grams of nitrogen And we could keep going further into the future, and after every half-life, 5, years, we will have half of the carbon that we started. But we'll always have an infinitesimal amount of carbon. But let me ask you a question. Let's say I'm just staring at one carbon atom.

Let's say I just have this one carbon atom. You know, I've got its nucleus, with its c So it's got its six protons. It's got its eight neutrons. It's got its six electrons. What's going to happen? What's going to happen after one second? Well, I don't know. It'll probably still be carbon, but there's some probability that after one second it will have already turned into nitrogen What's going to happen after one billion years?

Well, after one billion years I'll say, well you know, it'll probably have turned into nitrogen at that point, but I'm not sure. This might be the one ultra-stable nucleus that just happened to, kind of, go against the odds and stay carbon So after one half-life, if you're just looking at one atom after 5, years, you don't know whether this turned into a nitrogen or not.

Now, if you look at it over a huge number of atoms. I mean, if you start approaching, you know, Avogadro's number or anything larger-- I erased that. I don't know which half, but half of them will turn into it. So you might get a question like, I start with, oh I don't know, let's say I start with 80 grams of something with, let's just call it x, and it has a half-life of two years. I'm just making up this compound. And then let's say we go into a time machine and we look back at our sample, and let's say we only have 10 grams of our sample left.

Science Biology History of life on Earth Radiometric dating. Carbon 14 dating 1. Carbon 14 dating 2. Atomic number, atomic mass, and isotopes. Video transcript What I want to do in this video is kind of introduce you to the idea of, one, how carbon comes about, and how it gets into all living things.

Half-life and carbon dating (video) | Nuclei | Khan Academy

And then either later in this video or in future videos we'll talk about how it's actually used to date things, how we use it actually figure out that that bone is 12, years old, or that person died 18, years ago, whatever it might be. So let me draw the Earth. So let me just draw the surface of the Earth like that. It's just a little section of the surface of the Earth. And then we have the atmosphere of the Earth. I'll draw that in yellow.

File usage on Commons

So then you have the Earth's atmosphere right over here. Let me write that down, atmosphere.

And I'll write nitrogen. Its symbol is just N.

• Carbon 14 Dating - Math Central?
• worst dating advice funny.
• File history.
• .

And it has seven protons, and it also has seven neutrons. So it has an atomic mass of roughly Then this is the most typical isotope of nitrogen. And we talk about the word isotope in the chemistry playlist. An isotope, the protons define what element it is. But this number up here can change depending on the number of neutrons you have. So the different versions of a given element, those are each called isotopes. I just view in my head as versions of an element. So anyway, we have our atmosphere, and then coming from our sun, we have what's commonly called cosmic rays, but they're actually not rays.

You can view them as just single protons, which is the same thing as a hydrogen nucleus.

Radiometric dating

They can also be alpha particles, which is the same thing as a helium nucleus. And there's even a few electrons.

And they're going to come in, and they're going to bump into things in our atmosphere, and they're actually going to form neutrons. So they're actually going to form neutrons. And we'll show a neutron with a lowercase n, and a 1 for its mass number. And we don't write anything, because it has no protons down here. Like we had for nitrogen, we had seven protons.

So it's not really an element.