A helium nucleus has two protons and two neutrons. How
many elect...

Question

A helium nucleus has two protons and two neutrons. How
many electrons does it take to equal the mass of a helium
nucleus?

Accepted Answer

Hey everyone in this example, we need to find the number of electrons that have a total mass equal to that of a lithium nucleus. Our first step is to find lithium on our periodic tables and we see that it's in group one a. And that corresponds to the Molar mass 6.9 four g per mole. So now that we have our moller massive lithium, we can also understand that molar mass is the same thing as atomic mass. Whereas atomic mass is just written in units of emu. So we can go ahead and actually around this to about seven am you. So now that we have that we're going to also go ahead and because we need to find a number of electrons and right now, the only information we know is our units of our lithium nucleus in am you. We want to recall the conversion factor that we have for one a.m. u A value of 1837 electrons. And so we're going to find our number of electrons by taking Our seven a.m. use of lithium. And going ahead to I'm sorry, we don't really need to plug in lithium. We can just say seven a.m. You because the question just tells us that the total mass is equal to that of a lithium nucleus. So we can go ahead and just begin with a seven a.m. Use in general. And we're gonna go ahead and go from a m U two electron as our final unit. So we can go ahead and substitute that conversion factor in this fraction here. So in our denominator we'll just plug in one a.m. you for 1837 electrons. This allows us to cancel our units of am us leaving us with electrons or in this case number of electrons, which is what we want and what we're going to get is seven times 1008, 1837 for our final answer. So this is going to give us a value Of 12859 electrons total. And so this completes this example as our number of electrons. So I hope that everything be reviewed was clear. If you have any questions, please leave them down below and I will see everyone in the next practice video.

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