Why Are Proton-Proton and Neutron-Neutron Bonds More Stable in Atomic Nuclei?

In summary, the conversation discusses the preference for proton-proton and neutron-neutron bonds in the nucleus, as seen in the pairing term of the semi empirical mass formula. It is noted that nuclear physics differs from chemistry, as individual nucleon-nucleon bonds are not considered in the formation of nuclei. The pairing term is thought to be related to the shell model, where the alignment of spins is more stable with different orbitals. The Pauli exclusion principle (PEP) is mentioned as a factor in the formation of deuterium, as the combination of pn is favorable due to isospin issues.
  • #1
jeffbarrington
24
1
I am curious as to why proton-proton, neutron-neutron bonds are preferable in the nucleus; the pairing term in the semi empirical mass formula for the nucleus comes from the fact that pp and nn bonds are more stable in the nucleus (higher binding energy or more negative potential energy, however you want to look at it) whereas when talking about the formation of simple, two nucleon particles, the only one allowable is np, i.e. deuterium because of the PEP. Why isn't the PEP applying in the nucleus? Why does the pairing term not favour np bonds?
 
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  • #2
Nuclear physics is not chemistry. You don't make nuclei by considering individual nucleon-nucleon bonds. Each nucleon feels the potential created by the other nucleons.
 
  • #3
Vanadium 50 said:
Nuclear physics is not chemistry. You don't make nuclei by considering individual nucleon-nucleon bonds. Each nucleon feels the potential created by the other nucleons.
Of course, but the pairing term of the SEMF is to be thought of as being to do with pp and nn pairs in the nucleus. Is this an effect of the shell model? Like how in atoms it's lower energy (high binding energy) for the spins to be aligned if the electrons are all in different orbitals?
 
  • #4
Nuclei can have spin up and down, every available energy level can get two neutrons or protons, respectively. That makes pairs favorable, the next (odd) nucleon has to occupy a higher energy level.
 
  • #5
jeffbarrington said:
two nucleon particles, the only one allowable is np, i.e. deuterium because of the PEP

What is the PEP? I thought the combination pn was favorable because of isospin issues?
 

What is the difference between pp, np, and nn bonds?

PP, NP, and NN bonds refer to the types of chemical bonds formed between atoms. PP bonds are formed between two positively charged atoms, NP bonds are formed between a positively charged atom and a negatively charged atom, and NN bonds are formed between two negatively charged atoms.

How is the energy of a pp, np, or nn bond calculated?

The energy of a chemical bond is determined by the difference in energy between the bonded atoms and the separate atoms. This energy difference is known as the bond energy and is typically measured in units of kilojoules per mole (kJ/mol).

Which type of bond is the strongest: pp, np, or nn?

The strength of a chemical bond is determined by the distance between the bonded atoms and the type of atoms involved. Generally, pp bonds are the strongest, followed by nn bonds, and then np bonds.

What factors affect the energy of a pp, np, or nn bond?

The energy of a chemical bond can be affected by several factors, including the types of atoms involved, the distance between the bonded atoms, and the presence of any other nearby atoms or molecules.

How does the energy of a pp, np, or nn bond affect the stability of a molecule?

The energy of a chemical bond can greatly impact the stability of a molecule. Stronger bonds result in more stable molecules, as they require more energy to break. This stability is important for many biological processes, as well as in industrial applications.

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