stable and unstable isotops (1 Viewer)

[mitch_f1]

Hey
Just doing some questions from the textbook for nuclear chemistry (conquering chemistry 4th edn-HSC) and I came across a question that says:

'By comparing each of the following ioptopes with data for the element in the perioidic table, decide whether you wouldexpect it to be stable or not. Give your reason. Which, if any would you expect to be beta emitters"

For this question i used the zone of stability data (if Z<20 then n: p = 1.0, if Z=50 n: p = 1.3, if Z=80 n: p = 1.5, Z>83 instable)

In the question it lists 138,56 Ba, and 35,18 Ar, amongst many others.

The answers say that 138,56 Ba is stable, but it's n: p is 1.46 (putting it outside the zone of stability), and the answers say that 35,18 Ar is unstable, but it's n: p = 0.9 (putting it well inside zone of stability).......is this just a typo, or am I missing something.


Also, from the data given (atomic mass, atomic number, element name) how are you able to predict their ability to be beta/alpha emitters???


Thanks
Mitch

 

[mitch_f1]

no-one?

 

[Naylyn]

Have a look at the conquering chemsitry website they have a list of errors there.
If no-one else has answered this by this afternoon by the time I get home I'll give it a go.

 

[Naylyn]

For elements with attomic number 20 or less the ratio of neutron to protons should be about 1:1 for it to be stable, however as the atomic number get greater there needs to be more protons than neutrons for it to be stable.

Also if you look at the elements from 1-20 you will notice that nearly all of the elements have more neutrons than protons and so since there are more protons than neutrons in Ar 35, 18 it will be unstable.

Also if you look at the periodic table you will notice that the atomic mass of Ba 138, 56 is close to the average atomic mass given, suggesting that it will be stable, Ar 35, 18 however has a much lower atomic mass than the average suggesting that it will be unstable.

 

[mitch_f1]

Awesome, thanks heaps

Mitch

 

[Felix Jones]

bit late...but for all those who will reads this post later....the instability can come from both high n: p ratio and low n: p ratio...so 0.9 might be too low for the element.