Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Fida on August 21, 2016, 01:28:21 AM
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Hello!
"When nuclei are formed some of the mass is converted to energy,so that is why relative isotopic masses are not whole numbers."
What does this statement mean? Nuclei formed from what? How does mass convert to energy?
Thanks!
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Start from http://www.chemicalforums.com/index.php?topic=65859.0
then read
https://www.wikiwand.com/en/Nuclear_binding_energy#/Mass_defect
or
texbook on general chemistry
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[...] mass convert to energy
That's a common formulation but it's misleading. A better one could look like "every energy has a mass".
Kinetic energy for instance increases the mass of a moving object. Well, some Relativity specialists call "mass" only the rest mass and use some longer wording for mass+energy. I don't care.
The strong interaction that keeps the protons and neutrons together has a mass. Because it's attractive, the energy of the composite nucleus is less than its separate constituents, and so is the mass of the nucleus. If 4He is formed from two protons and two neutrons (over a complicated reaction path), the energy of the helium is less and the difference gets released during its formation.
The electrostatic interaction between the protons has a mass too. This one is repulsive, so it increases the nucleus' mass. Nuclei exist only because the strong interaction overwhelms the electrostatic repulsion, but as bigger nuclei have more and more protons, the electrostatic repulsion increases more quickly, so nuclei can't be too big. You observe that the nucleus' mass defect per nucleon decreases beyond iron.
Beyond lead, well before the size where nuclei would explode into protons and neutrons, they find ways to split into more favourable rearrangements. The most common one is to expel an alpha particle, that's alpha radioactivity. Sometimes heavy nuclei split into two or three smaller ones, that's fission.
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[...] mass convert to energy
That's a common formulation but it's misleading. A better one could look like "every energy has a mass"
I like that one. Really answers the question in one statement. +1
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I read the rules before posting,did I break any?
Thanks a lot for the link and the post.
So,energy has mass I did not know that.Now,what attraction is there between proton and neutron? I understood from your explanation that attractive forces decrease mass and repulsive forces increase mass.
The strong interaction that keeps the protons and neutrons together has a mass. Because it's attractive, the energy of the composite nucleus is less than its separate constituents, and so is the mass of the nucleus. If 4He is formed from two protons and two neutrons (over a complicated reaction path), the energy of the helium is less and the difference gets released during its formation.
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Now,what attraction is there between proton and neutron
https://www.wikiwand.com/en/Nuclear_binding_energy
Read nuclear force under this topics
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I see,nuclear force holds them together.
Thanks a lot