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NOVA ScienceNOW

Island of Stability

  • Teacher Resource
  • Posted 08.09.07
  • NOVA scienceNOW

In this video segment adapted from NOVA scienceNOW, learn how nuclear chemists are conducting their search for new elements. Scientists have encountered tremendous challenges working with heavy elements—those whose atomic weights exceed anything nature has created—because of the atomic forces at work, which include electromagnetic forces and the strong nuclear force. This video explores the concept of an "island of stability"—a stable new element that scientists predict should be possible to create amidst highly unstable and fleeting ones.

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NOVA scienceNOW Island of Stability
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  • Media Type: Video
  • Running Time: 6m 52s
  • Size: 20.5 MB
  • Level: Grades 9-12

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Source: NOVA scienceNow: "Island of Stability"

This media asset was adapted from NOVA scienceNOW: "Island of Stability".

Background

An element is defined according to the number of protons contained inside the nucleus of each atom. No two elements have the same number of protons, hence each element has a unique atomic number. The periodic table lists 90 naturally occurring elements—meaning those created in the aftermath of the Big Bang or later forged in the heat and pressure of stars. A further 28 elements have been created by humans in a laboratory setting.

The higher its atomic number, the heavier and less stable an element is. Elements are considered stable when the repulsive force that exists between positively charged protons is effectively countered by another force, the strong nuclear force, which corrals protons and chargeless neutrons and prevents them from bursting out of the nucleus. Heavy elements are unstable because their atoms contain lots of protons. While the strong force is about 100 times stronger than the electromagnetic repulsion between two protons, it is a short-range force. The electromagnetic force begins to overwhelm the strong force as the number of protons in a nucleus approaches 100 and the nucleus becomes over-large. When breakup, or decay, occurs, the energy pent up inside the nucleus is released in the form of radiation and a spray of particles.

Scientists have proven that it is possible to create new heavy elements artificially by taking an existing element and adding protons and neutrons—together called nucleons—to its nucleus. Frequently, they do this by bombarding an atom with nucleons with the hope that these nucleons are successfully incorporated into the nucleus. But as more protons are added to a nucleus, their tendency to repel one another gets stronger and stronger. Consequently, experimental heavy atoms tend to rip apart almost instantaneously. Their very brief existence makes it difficult for scientists to study their characteristics for potential applications in science.

The nuclear chemists trying to create element 114 are hopeful that this heavy atom would be longer-lived. Since the 1950s, scientists have viewed atomic nuclei as being built up in rings, a model similar to that of electron shells within the atom. According to this revised model, a ring filled with very precise numbers of protons and neutrons would give an element stability, even if elements nearby on the periodic table were highly unstable. For example, certain forms, or isotopes, of thorium (atomic number 90) and uranium (92) are the only naturally occurring atoms heavier than bismuth (83) that are relatively stable amidst other, far less stable elements. The elusive element 114 discussed in this video segment is, hypothetically, another "island of stability" in a "sea of instability." Scientists just have to find a way to get the "magic numbers" of 114 protons and 184 neutrons inside a nucleus.

To learn more about how the periodic table arranges elements and can even help predict characteristics of new ones, check out Periodic Table of the Elements and Graphing the Periodic Table.

To learn more about how we know that Earth's naturally occurring elements were created in stars, check out The Origin of the Elements.

To learn more about the structure of atoms, check out Atoms: The Space Between and Atom Builder.

To learn more about the strong nuclear force, check out String Theory: Gravity - The Odd Man Out.

Find viewing ideas for this video segment on NOVA Teachers.

Questions for Discussion

    • What explanation is proposed for the observation that protons with like charges (+) can stay close together in the nucleus of an atom? Why don't they repel each other right out of the nucleus?
    • What is meant by the "island of stability"? Why is it called an island?
    • What reasoning did the scientists use to predict the properties of element 114?
    • Why do you think it is so very difficult to have a direct collision between nuclei? Is it something to do with the size of the particles? Their charge?
    • What other combinations of two elements would, mathematically at least, yield the nucleus of element 114?

Resource Produced by:


					WGBH Educational Foundation

Collection Developed by:


						WGBH Educational Foundation

Collection Credits

Collection Funded by:


						National Science Foundation



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