[jarceo]

The question reads:
There are two different Bromine isotopes. Under normal conditions,elemental bromine consist of  Br₂molecules.  and the mass of a Br₂ is the sum of the masses of the two atoms in the molecule. The mass spectrum of Br₂ consist of 3 peaks.
Mass (amu)      Relative Size
157.836              0.2569
159.834              0.4999   
161.832              0.2431

A) What is the origin of each peak? ( of what Isotopes does it consist)
B) What is the mass of each isotope?
C) Determine the  average  molecular mass  of Br₂ molecule
D) Determine the atomic  mass of a single bromine atom
E) Calculate the Abundance of the two molecule??

[Borek]

Please read forum rules. You have to show that you tried.

[jarceo]

Well, I asked my professor for help on this problem and he steered me in the right direction and then I got stuck.  So I graphed the peaks, (and the peaks are the abundances of the particular isotopes) Then I calculated the average atomic mass number by multiplying the abundance by the isotope mass no. I am now lost, because I have to calculate the average mass of a Br atom. I figure because the mass of the isotopes are of the diatomic Br species then all I have to do is divide the mass no. and do the same process for the atom's average mass. What I do not understand is that the question asks for the abundance of 2 isotopes,  are these 79 and 81??

[Borek]

There are two types of Br atoms, that gives three types of Br molecules - do you know why? In fact there are four types, just two of them are identical.

Lightest molecule - what isotopes does it contain? Half of the mass of this molecule - what does it equal?

[jarceo]

The lightest molecule- mass of 157.832 this is the Br -79 Isotope and half the mass is  39.459.? Right?

[Borek]

No, 39 seems to be a quarter.

[jarceo]

oh ok MOLECULE the key word. Sorry.... 1/2 mass is 78.916