MadSci Network: Chemistry

Re: Universe has many elements.Do all elements break down into Hydrogen

Date: Tue Oct 31 11:48:21 2000
Posted By: Tony Gaglierd, Faculty, Natural Science and Engineering Technology, Point Park College
Area of science: Chemistry
ID: 972660141.Ch

Dear Mr. McGannon

I gather you teach 7th grad science. You have quite an intelligent and curious group.

There are several parts to your question.

By definition an element is a substance that cannot be broken down into any simpler substance. As such elements cannot be broken down to hydrogen.

The next part of you question deals with the formation and development of the elements. Approximately 15 billion years ago the universe began as an extremely hot and dense region of radiant energy. The Big Bang. Immediately after the formation, it began to expand and cool. As the universe cooled, sub atomic particles, known as quarks condensed to form nucleons. This process is similar to the way steam condenses to water droplets as water vapor cools. Further expansion and cooling allowed the neutrons and some protons (hydrogen atoms) to fuse to form helium nuclei.

Substantial quantities of nuclei more massive than hydrogen were not made in the Big Bang. After about a billion years, clouds of cold atomic hydrogen and helium gas began to be drawn together. As they contracted to higher densities the clouds warmed. When the temperature reached a few million degrees Kelvin, nuclear reactions began in the cores of these massive stars.

Stars the size of the Sun will burn hydrogen into helium until the hydrogen is exhausted. At this point the cores of the star contracts and heats up until a fusion reaction of three helium nuclei are converted into carbon. At this stage the stare is known as a red giant.

Higher mass stars have higher internal temperatures than our sun and they are capable of fusing carbon into oxygen. In very massive stars, the fusion reaction can produce successively more massive nuclei all the way up to iron. Atomsí more massive than iron is produced by the capture of neutrons by atoms during the few moments of the explosion of a super nova. The sequence of such a reaction can produce elements all the way up to uranium 238.

Some books and articles on the origin of elements are:

Steven Weinberg, the First Three Minutes. Basic Books, New York, 1993

David Lindley, The End of Physics, Basic Books, New York, 1993

Radioactive elements both natural and manmade do under go nuclear decay and depending on the type of emission that occurs they do change into other elements but only to the stable form in the decay series. For naturally occurring radioactive elements they decay back to lead. Man-made elements decay back to the next stable element in the series in the periodic table.

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