I understand that this is the most basic knowledge of moles, however I'm still unsure - according to easy research, $\ce{O2}$ forms a mole of Oxygen. As a mole is $6.022*10^{23}$, exactly what on the periodic table can we use to find out that it's 2 Oxygen in one mole? Wouldn't it be $6.022*10^{23}$, instead of 2?

  • $\begingroup$ Welcome to chemistry.SE! You can visit the help center for questions you might have about our community. Or, you can just start by taking a little tour.||By the way, I really don't get your question. What has 2 in $\ce{O2}$ to do with the Avogadro number? I think you've misunderstood the concept of mole. $\endgroup$
    – M.A.R.
    Jan 15 '15 at 23:07
  • $\begingroup$ I'm very familiar with the stack exchange websites, however thanks for trying. Regarding the comment - That's exactly what I'm wondering. I've found One mole of oxygen gas, which has the formula O2. - Found at this link $\endgroup$
    – user12777
    Jan 15 '15 at 23:10

$\rm O_2$ is the most common form of oxygen---the periodic table won't really tell you that.

Avogadro's number tells you how many particles there are in a mole.

There are $6.022\times 10^{23}$ O atoms in a mole of O atoms.

There are $6.022\times 10^{23}$ $\rm O_2$ molecules in a mole of $\rm O_2$.

Since you have 2 oxygen atoms in one $\rm O_2$ molecule, there are $2\times 6.022\times 10^{23}$ O atoms in a mole of $\rm O_2$.

Do you see the difference?


A 'mole' is not short for a 'molecule'.

The 'mole' is a specific quantity (number of objects) defined by Avogadro's constant $N_A=6.022\times10^{23}mol^{-1}$. So a 'mole' of oxygen molecules has $6.022\times10^{23}$ molecules.

The '2' in $O_2$ means there are two oxygen atoms in an oxygen molecule.


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