Anonymous asked in Science & MathematicsChemistry · 3 weeks ago

Atomic Mass?

Since the average atomic mass of hydrogen is 1.0079 and hydrogen is composed of one proton and one electron then why isn't the average atomic mass of Helium exactly 4.0316(4x1.0079)?  

(Helium has an average atomic mass of 4.0026)

2 Answers

  • DrBob1
    Lv 7
    3 weeks ago

    As said, a He atom is made of 2 protons and 2 neutrons which do have different weights.  But I think the question goes back further in time.  The He nucleus is formed in a star from 4 H atoms.

    The difference in mass is what you see as sunshine.  Einstein showed us why:  e = mc^2

  • 3 weeks ago

    Because helium does not consist of four protons and four electrons. A helium nucleus usually contains 2 protons and 2 neutrons. Protons and neutron have slightly different masses.

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