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Physics question on isotopes

The question is: Potassium-40 decays to argon-40
a. What is the atomic number of potassium?
b. What is the atomic number of argon?
c. What must happen to one of the protons?
d. How can you ensure that the charges are conserved?
e. Write and equation to show this decay.
My answers where a - 19 b - 18 c - Formed by a neutron becoming a proton + electron d - An election is formed
e:
4019K + beta particle ----> 4018Ar
Am I along the right path or am I completely wrong I'm not as sure my teacher didn't really explain too well in class?
You're right about parts a and b. However, the atomic number of argon is one LESS than the atomic number of potassium, so you can't possibly have gained a proton - something must have happened to one of the protons in potassium. Do you know about beta plus decay?
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james113
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Original post by MrLatinNerd
You're right about parts a and b. However, the atomic number of argon is one LESS than the atomic number of potassium, so you can't possibly have gained a proton - something must have happened to one of the protons in potassium. Do you know about beta plus decay?


Does a neutron in the nucleus change into a proton and an electron in the potassium therefore potassium gains a proton

Would the equation be: 40/19K--> 40/18Ar + Beta particle?
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Mo H
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Try this video, see if it helps: https://www.youtube.com/watch?v=HwVFaiUpe3Q
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james113
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Original post by Mo H
Try this video, see if it helps: https://www.youtube.com/watch?v=HwVFaiUpe3Q


Thanks, the video has helped my overall understanding.

From the video according to the general formula the equation should be:
4019K --> 4020Ar + 0-1Beta

if thats right then was the question about atomic number of argon just to throw you off?
Reply 5
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Mo H
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As explained in the video, with beta- decay, Potassium-19 would decay into Calcium-20. So the question seems like it is referring to beta+ decay, which would be unusual at GCSE.
Beta+ decay involves a proton turning into a neutron and a positron, which is emitted from the nucleus, hence the proton number decreasing by 1 and the mass number remaining the same. I don't think this was in the video as it is not usually included in GCSE Physics. Sorry if I caused any confusion.

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