How many protons and how many neutrons are in (a) 3He, (b) 20Ne, (c) 60Co?

Please help! I know how to find basic protons and neutrons, but I am obviously missing something here! Any explanation would be wonderful.

How many protons and how many neutrons are in (a) 3He, (b) 20Ne, (c) 60Co?

N (He)

Z (He)

Z (Ne)

N (Ne)

Thank you in advance!

1 Answer

  • You need a periodic table or similar.

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    For 3He (helium-3):

    1) Look up helium’s atomic number (e.g. from the periodic table).

    You will find it is 2 That means it contains 2 protons. Z=2.

    (You should probably remember this as it is physics ‘general knowledge’; also remember that hydrogen has atomic number=1.)

    2) We are looking at 3He. The ‘3’ is the total number of protons + neutrons. To get the number of neutrons, subtract Z from 3.

    3-2=1. So there is 1 neutron. N=1.

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    The same method is used for 20Ne and 60Co.

    If that’s not clear, watch the first 3 or 4 minutes of the video in the link, which explains this more clearly.

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