# Question #a31cd

Aug 14, 2016

Those are mass numbers of each molecular isotope, meaning those of ${\text{Br}}_{2}$. Bromine is naturally a diatomic liquid.

It doesn't mean that there are three naturally-existing atomic isotopes, but it does mean that one $\text{Br}$ on ${\text{Br}}_{2}$ doesn't necessarily have to be $\text{_(35)^(81) "Br}$ if the other is $\text{_(35)^(81) "Br}$, for example.

Add up the mass numbers and you should see that:

$79 + 79 = \textcolor{g r e e n}{158}$
$79 + 81 = \textcolor{g r e e n}{160}$
$81 + 81 = \textcolor{g r e e n}{162}$

That means you have the three naturally-existing isotopic molecules:

$\textcolor{b l u e}{\text{_(35)^(79) "Br"-""_(35)^(79) "Br}}$

$\textcolor{b l u e}{\text{_(35)^(79) "Br"-""_(35)^(81) "Br}}$

$\textcolor{b l u e}{\text{_(35)^(81) "Br"-""_(35)^(81) "Br}}$

Therefore, you still have:

• Two naturally-existing atomic isotopes.
• Due to the diatomic nature of naturally-existing bromine liquid, three combinations of atoms are possible, generating three naturally-existing molecules containing the three different combinations of atomic isotopes.