Is it possible to deduce the number of protons from the mass

  • Context: High School 
  • Thread starter Thread starter rwooduk
  • Start date Start date
  • Tags Tags
    Mass Protons
Click For Summary

Discussion Overview

The discussion revolves around whether it is possible to deduce the number of protons in an isotope, specifically Lead-208 (208Pb), based solely on its mass number. Participants explore the relationship between mass number, the number of protons, and neutrons, as well as implications for decay modes of isotopes.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that the number of protons is defined by the element's symbol (Pb for lead), and the mass number (208) represents the total number of protons and neutrons, not allowing for the deduction of the number of protons alone.
  • Others argue that when the full notation (208Pb) is provided, one can deduce that there are 82 protons and 126 neutrons based on the identity of the element.
  • A participant questions whether the lack of energetically favorable decay modes for Lead-206 can be deduced from its mass number or if additional information is necessary.
  • Some participants mention that while 206 is not sufficient information to determine decay modes, there may be nuclear models that could predict decay based on known proton and neutron numbers.
  • There is a discussion about the potential misunderstanding of the original question regarding the deduction of protons from just the mass number.

Areas of Agreement / Disagreement

Participants generally disagree on whether the mass number alone can provide information about the number of protons. While some maintain that only the element's symbol provides that information, others contend that specifying the isotope allows for the deduction of proton and neutron counts.

Contextual Notes

Participants note that understanding the decay modes of isotopes may require looking up additional information about possible decay products, indicating that the discussion involves complexities that are not fully resolved within the thread.

rwooduk
Messages
757
Reaction score
59
...number?

If you are give say Lead, 208Pb. What is the 208? and is it possible to deduce the number of protons Z from it with no other information?

Haven't done chemistry yearts so any help would be appreciated.
 
Physics news on Phys.org
Nope. Number of protons is defined by the Pb symbol. 208 is sum of number of protons and neutrons (number of nucleons), and doesn't tell anything about how many of each there is.

It is also not uncommon to have several isotopes of different elements all having the same total number of nucleons, these are called isobars.
 
  • Like
Likes   Reactions: rwooduk
Borek said:
Nope. Number of protons is defined by the Pb symbol. 208 is sum of number of protons and neutrons (number of nucleons), and doesn't tell anything about how many of each there is.

It is also not uncommon to have several isotopes of different elements all having the same total number of nucleons, these are called isobars.

Many thanks for that, the lecturer seemed to assume we knew, no other info was given in class. So youre reply is reassuring thanks!

One more thing if you have a free minute, for Pb 206, he said that there are no energetically favourable decay modes, can this be deduced from the 206 value? or would more information be required? or it is common knowledge and something to memorise?
 
It is not a chemistry question - I will move the thread to nuclear physics. 206 is definitely not enough, but perhaps there are nucleus models that allow predicting decay modes from known Z and A.
 
  • Like
Likes   Reactions: rwooduk
Borek said:
It is not a chemistry question - I will move the thread to nuclear physics. 206 is definitely not enough, but perhaps there are nucleus models that allow predicting decay modes from known Z and A.

Ok. Many thanks for your replies!
 
Borek said:
Nope. Number of protons is defined by the Pb symbol. 208 is sum of number of protons and neutrons (number of nucleons), and doesn't tell anything about how many of each there is.
Am I misreading something here?

If you have a mass composed of Pb208, as the OP specified, then all the atoms contain 82 protons and 126 neutrons.

If they didn't, they would either not be the 208 isotope, or they would not be lead at all..
 
DaveC426913 said:
Am I misreading something here?

If you have a mass composed of Pb208, as the OP specified, then all the atoms contain 82 protons and 126 neutrons.

If they didn't, they would either not be the 208 isotope, or they would not be lead at all..

Did you deduce the bolded statement from the Pb208? Is there any chance that you could explain how?
 
Yes.

(My 'shut up and keep your head down' alarms are going off in my head, so it is against my better judgement that I'm challenging Borek, but) it seems to me that
- you specified the mass contains entirely Pb208
- lead contains 82 protons, so the rest (126) are neutrons.

Here it is, listed in the isotopes of lead chart:
http://en.wikipedia.org/wiki/Isotopes_of_lead

208Pb 82 126 207.9766521
 
  • Like
Likes   Reactions: rwooduk
DaveC426913 said:
Am I misreading something here?

Definitely there is some misunderstanding, could be my English failed.

As far as I understand the original question asked "is it possible to deduce number of protons from a single 208 number" - and then the answer is "no". At the same time when you are given entire "208Pb" information number of protons is given by the identity of the element, given by its symbol (and I believe that's what I wrote).
 
  • #10
Borek said:
Definitely there is some misunderstanding, could be my English failed.

As far as I understand the original question asked "is it possible to deduce number of protons from a single 208 number" - and then the answer is "no". At the same time when you are given entire "208Pb" information number of protons is given by the identity of the element, given by its symbol (and I believe that's what I wrote).
That's what I thought you were saying, yes. Given only 208, you do not know which element it is, and thus the ratio of protons/neutrons.

But the OP did specify Pb208. Which is enough to deduce the ratio.
 
  • #11
rwooduk said:
One more thing if you have a free minute, for Pb 206, he said that there are no energetically favourable decay modes, can this be deduced from the 206 value? or would more information be required? or it is common knowledge and something to memorise?
You have to look up the masses of possible decay products to see if the decays are possible. It is possible to estimate them theoretically but to do that precisely is way beyond the scope of homework problems. Alternatively, look up directly if the nucleus is stable.
 

Similar threads

Undergrad Probing into protons with high-energy particles
  • · Replies 10 ·
Replies
10
Views
2K
High School Fundamental particles and mass quantization
  • · Replies 13 ·
Replies
13
Views
3K
High School Why does the nucleus become unstable as the number of nucleons increases?
  • · Replies 12 ·
Replies
12
Views
5K
High School Explaination of beta + decay in layman language
  • · Replies 1 ·
Replies
1
Views
2K
High School Free Proton verses Nucleus Proton rest mass
  • · Replies 2 ·
Replies
2
Views
2K
High School How many gluons on average are there in a proton at once?
  • · Replies 9 ·
Replies
9
Views
3K
Undergrad Neutron/proton nucleon destruction by acceleration
  • · Replies 7 ·
Replies
7
Views
3K
Undergrad How powerful would a collider have to be to observe a sphaleron?
  • · Replies 2 ·
Replies
2
Views
3K
Undergrad Does the Higgs Field Consist of Higgs Bosons?
  • · Replies 8 ·
Replies
8
Views
3K
Undergrad What Are the Complexities of Radioactive Isotopes in Nuclear Chemistry?
  • · Replies 6 ·
Replies
6
Views
2K