The Wikipedia article on the mole states:

 The term gram-atom (abbreviated gat.) has been used for a related but distinct concept, namely a quantity of a substance that contains Avogadro's number of atoms, whether isolated or combined in molecules. Thus, for example, 1 mole of $\ce{MgB2}$ is 1 gram-molecule of $\ce{MgB2}$ but 3 gram-atoms of $\ce{MgB2}$.

Can anybody explain the difference between moles and gram atoms, and how is it that 1 mole of $\ce{MgB2}$ is 1 gram-molecule of $\ce{MgB2}$ but 3 gram-atoms of $\ce{MgB2}$?

  • $\begingroup$ The molecule has 3 atoms, so ...... $\endgroup$ – ChemExchange Apr 13 '15 at 15:14

$\ce{MgB2}$ is 1 gram-molecule of $\ce{MgB2}$ but 3 gram-atoms of $\ce{MgB2}$.

Why is this so? Let us consider this problem in the familiar mole:

If we were asked how many moles of the substance (molecule) were in this, we would state 1 mole, if there were $\pu{45.3 g}$ of substance. However, if we were asked how many moles of atoms were in the substance, we would accordingly state 3. Thus, in one molecule, there are 3 atoms, so if we simply consider the number of atoms, there would be the necessity of counting the number. of atoms in a molecule, as a molecule is comprised of more than a single atom

* This is purely hypothetical. One would probably not consider $\ce{MgB2}$, as J. LS pointed out, it decomposes . However, the concept can be applied to other compounds

  • $\begingroup$ There are no molecules of magnesium diboride as it decomposes before you can reach its melting point, which makes this a rather odd example to use here. $\endgroup$ – J. LS Apr 14 '15 at 8:19
  • $\begingroup$ @J.LS Thanks for pointing that out! I had simply used the example the asker had given, but I guess it would be nice to be aware of that point. $\endgroup$ – Andy Apr 14 '15 at 22:13
  • $\begingroup$ OP has also asked for difference between moles and gram atoms ,but nobody explained this point? $\endgroup$ – Rabik John May 12 '18 at 11:15

protected by orthocresol Jun 28 '17 at 18:07

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.