| MadSci Network: Chemistry |
There are basically two factors that affect the “stability” of larger atoms: ratio of the number of protons to neutrons and nucleus size. First, the two basic forces in a nucleus are one of attraction and one repulsion. Specifically, they are the "strong" nuclear force holding protons and neutrons together (binding energy) and the electrostatic force of protons repelling each other (Coulomb force). Under certain arrangements (ratios) of protons and neutrons, the electrostatic forces balance each other and the binding energy holds the nucleus together. However, any other ratio of protons and neutrons where the electrostatic forces are not balanced, instability is created in the nucleus causing it to decay. The atom will continue to decay until it reaches a stable combination of protons and neutrons. Fundamentally, there are no stable nuclei with an atomic number (proton number) higher than 83 or a neutron number higher than 126. Included in the factor of proton and neutron ratios is a concept of “magic numbers”. These numbers are thought to be a geometric form of symmetry which create stability. They include the following numbers: 2, 8, 20, 28, 50, 82, 114, 126, 164. These magic numbers are applied separately to the number of neutrons and protons. This means a stable nucleus can have a neutron or proton number that is a magic number and the other not. Nuclei that have an odd number ratio of protons and neutrons is not as stable as one that may have one odd and one even number protons or neutrons. An even -even number of protons and neutrons is more stable than and even-odd ratio. In addition, having a proton or neutron number that is a magic number makes those nuclei even more stable. “Doubly magic” nuclei are extremely stable and have a combination of proton and neutron numbers that are both magic numbers; e.g. Helium has 2 protons and 2 neutrons, Oxygen has 8 protons and 8 neutrons and Lead has 82 protons and 126 neutrons. Next, the nuclear forces keeping the atom’s nucleus together are strong but are short range forces. The more protons in the nucleus, the more neutrons are needed for stability. However, the nuclear forces holding everything together eventually become weak as the size of nucleus grows. Or in more complex words, a more strong nuclear force is needed to compensate for the increasing Coulomb repulsion (proton-proton repulsion) in larger nuclei. This is the biggest factor in why the heaviest elements (atoms) are not as stable as smaller one. I hope this may begin to answer your question. For more information on nuclei stability and composition, you may want to look through the following websites: http://207.10.97.102/chemzone/lessons/11nuclear/nuclear.htm http://www.2bengineer.net/chemistry/ch5_3_2.html http://www.infodotinc.com/doenuclearphys/nuclearphysics17.htm http://hep.ucsd.edu/~branson/130/130b/130b_notes_prod/node128.html http://online.cctt.org/physicslab/content/PhyAPB/lessonnotes/dualnature/nuc lear.asp http://www.phys.ufl.edu/~acosta/phy3101/lectures/nuke2.pdf http://particleadventure.org/particleadventure/ Two research papers providing a detailed look at nuclide stability through geometric symmetry may be found at: http://www.phy.hr/~npavin/science/power_lawsCSF.pdf http://www.blazelabs.com/f-p-swave.asp
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