Question

The material covered in this homework assignment relates directly to stellar evolution. nucleosynthesis and abundance of the chemical elements in our solar system. The following plot may be helpful. Abundances of the chemical elements in the solar system in terms of atoms per 10 ^6 atoms of Si. The data were derived primarily by analysis of carbonaceous meteorites and by optical spectroscopy of light from the Sun and nearby stars. (Fig 2.2. Faurc) Compile the abundances of the rare earth Which other elements also lack stable isotopes? Why is lead (Pb) more abundant than we might expect?

Answer 1

1)Ans: Any element is determined by the number of protons not the number of Neutrons. The isotope is determined by the number of neutrons. Hydrogen without Neutrons is Hydrogen. Hydrogen with a neutron is deuterium, and if it has 2 neutrons it is called Tritium. Helium is produced in the first stage of a stars life cycle. 2 Hydrogen atoms (this includes deuterium and tritium) fuse together to yield helium and energy as well as a slight loss of mass. In later stages of a stars life cycle it starts producing ever heavier elements until if it is massive enough it goes supernova and a whole spectrum of elements are developed. As the universe ages more and more of the hydrogen is used up, but Hydrogen is still the most abundant element in the Universe.

2Ans: The radioactive promethium and cerium are exception – relatively plentiful in Earth's crust, with cerium being the 25th most abundant element at 68 parts per million, or as abundant as copper. Because of their geochemical properties, rare earth elements are typically dispersed and not often found concentrated as rare earth minerals in economically exploitable ore deposits. It was the very scarcity of these minerals.

  
3Ans: Tc is the lightest element with no stable isotopes, Technetium goes through beta decay and is used in nuclear medicine for diagnostic tests. Pm Promethium is also a beta emitter. Rather, it is each isobar (nuclides with the same fixed number of nucleons, either protons or neutrons) that contains at least one nuclide stable with respect to beta decay, because beta decay is between nuclides on the same isobar, and one must be minimum-energy and not capable of decaying to the others. (For masses 5, 8, and 210 and up, the beta-stable nuclide(s) can alpha decay, so there are no stable nuclides in those isobars.)

On earth Tc and Pm are products of the nuclear age, but they do exist in large stars in their later life cycles i.e. Red Giant stage through supernova, but because none of their isotopes are radiologically stable they do not last long in geological terms. The longest living Tc half life is 4.2 million years. That sounds like a long time but compared to the Earths age of about 4 billion years that is not very long therefore no matter how much had existed early on in Earth’s history, almost all of it would be long gone by now. Pm is even worse with a half life of about 17 years.

4Ans: Of the 80 elements with at least one stable isotope, 26 have only one single stable isotope. The mean number of stable isotopes for the 80 stable elements is 3.1 stable isotopes per element. The largest number of stable isotopes that occur for a single element is 10 (for tin, element 50).

All of the elements have some isotopes that are radioactive (radioisotopes), although not all of these radioisotopes occur naturally. The radioisotopes typically decay into other elements upon radiating an alpha or beta particle. If an element has isotopes that are not radioactive, these are termed "stable" isotopes. All of the known stable isotopes occur naturally (see primordial isotope). The many radioisotopes that are not found in nature have been characterized after being artificially made. Certain elements have no stable isotopes and are composed only of radioactive isotopes: specifically the elements without any stable isotopes are technetium (atomic number 43), promethium (atomic number 61), and all observed elements with atomic numbers greater than 82.

5Ans: Lead is likely to form compounds that do not sink into the core but that stay above on Earth in its crust, even though without sinking deep into it.