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Preliminary chem: How do I know which isotopes are stable and which ones aren’t? (1 Viewer)

HazzRat

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Given a list of isotopes, how will I know which ones are stable and which ones aren’t?
I have a list here and I wasn’t told how to catagorise them.
(Since I’m typing on phone, I’ll write the mass number and atomic number like [A, Z] element.)
  • [3, 1] H
  • [20, 10] Ne
  • [232, 90] Th
  • [37, 17] Cl
  • [231, 91] Pa
  • [197, 79] Au
  • [18, 8] O
  • [238, 92] U
 

synthesisFR

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Depends on 2 factors
1) mass of the nucleus, if Z>83 then they are unstable
2) neutron to proton ration: must be stable, u should learn about the zone of stability graph at school
 

HazzRat

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So do I just use the graph then and base it off that?
 

synthesisFR

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usually u just follow 1)
but 2) might be relevant if the graph is given in exams, although i don't know if many schools teach this graph but i think its kinda important to know why n : p ratio is important because u will learn that:
for alpha decay: u release size quickly
beta decay: fixes an inappropriate n : p ration as a neutron decomposes into an electron and proton, hence u loose a neutron but gain a proton.

however if ur school doesn't teach these details i don't think u need to worry because its not relevant for the HSC
however u could still do some in depth research through a good chemistry textbook
 

synthesisFR

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Idk tho i kinda over-study chemistry bc of tutoring so i learn a lot more in depth to understand how things work but at the same time idk if its really needed.
 

HazzRat

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usually u just follow 1)
but 2) might be relevant if the graph is given in exams, although i don't know if many schools teach this graph but i think its kinda important to know why n : p ratio is important because u will learn that:
for alpha decay: u release size quickly
beta decay: fixes an inappropriate n : p ration as a neutron decomposes into an electron and proton, hence u loose a neutron but gain a proton.

however if ur school doesn't teach these details i don't think u need to worry because its not relevant for the HSC
however u could still do some in depth research through a good chemistry textbook
Ok, I'm only in week four so we'll probably get to that later
 

synthesisFR

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My schools physics and chem faculty is kinda trash ngl some topics we just don't go into enough depth
and my tutoring sometimes goes overboard
which is why also get confused on what i am meant to know and what i don't because theres such a big difference
luckily a lot of my classmates are aware because they self study and do hsc questions
 

HazzRat

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Ok. My chem teacher is pretty good though so I will learn it eventually. One small problem is that I have fallen behind and so I will catch up on the weekend and write some decent notes. How did you study for chem? Did you write notes or just do practise questions?
 

wizzkids

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These points are from my teaching guidelines for the Preliminary Chemistry Course, on Module 1 Properties of Matter.
Students are not required to predict the stability of any particular nucleus.
Students are provided the graph of the band of stability of isotopes, showing atomic number A (number of protons) on the horizontal axis, and number of neutrons on the vertical axis.
Students recognise the following patterns in the graph:
  • Stable isotopes of the light elements contain approximately a ratio of 1:1 protons and neutrons.
  • As A increases, more neutrons than protons are required to maintain stability in the nucleus. The graph bends upwards.
  • If a light nucleus contains substantially more protons than neutrons, it is likely to be unstable and emit Beta+ radiation to rid itself of the excess positive charge.
  • If a light nucleus contains substantially more neutrons than protons, it is likely to be unstable and emit Beta- radiation to increase the number of protons and decrease the number of neutrons.
  • At Z = 200 the proton : neutron ratio increases to 1:1.5 and beyond Z = 208 there are no stable isotopes.
  • All nuclei beyond Z = 208 decay, usually by emission of alpha particles, because emission of an alpha particle will move the nucleus quickly towards the band of stability.
 

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