History. Use/Application through History

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1 Isotopes create variance within atoms of the same element. They are both created in nature as well as synthesized in laboratories and are used for a variety of helpful procedures in the modern era. History Explore the discoverer's biography, including general facts about his life and anecdotes regarding how he made this particular discovery. Also see other significant scientific discoveries built largely on this concept and other real-world applications in history that may not still be relevant. Discoverer/Developer Henri Becquerel ( ) discovered the existence of multiple masses for the same element when he realized a product of uranium's radioactive decay, ionium, was unable to be retrieved again by chemical means from the element thorium. Because chemical uniqueness is a defining characteristic of an element, it had to be concluded that ionium was not a new element, just a different variation of thorium. Frederick Soddy ( ) was an English scientist who worked along with Ernest Rutherford on his research with radioactivity; he was awarded for his identification of isotopes with the Nobel Prize in Chemistry in Soddy worked with Sir Ernest Rutherford in the McGill University, and hypothesized in 1913 that elements existed with different atomic masses that were chemically inseparable and indistinguishable. He concluded that these were all the same element and should reside in the same place on the periodic table. He coined these different atoms in the same element isotopes. Use/Application through History The discovery of different atomic masses for the same element shattered Dalton's theory that atoms interacted with each other differently based on their atomic mass. The defining characteristics of elements became their number of protons as well as them being chemically indistinguishable from another element. Different isotope masses for every element also led to the discovery of mass spectroscopy by Francis William Aston ( ), which greatly increased the accuracy of calculating atomic masses of different isotopes and elements. Mass spectroscopy measured the mass of elements to a much higher degree of accuracy than anything before it. Aston soon found the principle isotopes for almost all the elements as well as their abundance. He was awarded the Nobel Prize for Chemistry in 1922 for his extensive identification of isotopes. 1 / 6

2 Concept Definition Study the primary definition of this concept, broken into general, basic, and advanced English definitions. Also see the mathematical definition and any requisite background information, such as conditions or previous definitions. General Science The nucleus of an atom is made up of protons (positive particles) and neutrons (neutral particles). Isotopes are atoms that have the same number of protons, thus they are the same element; however they have different numbers of neutrons. Basic The defining characteristic of unique elements is the number of protons they possess, which also is the number of electrons when the element is not charged. What can vary with atoms within the same element are the number of neutrons that reside with the protons in the nucleus. Atoms with a different number of neutrons, but the same number of protons, are known as isotopes. Isotopes will have different atomic masses because neutrons have almost the same mass as protons. Advanced Although all atoms in the same element have an equal number of protons, they often vary in the number of neutrons they contain; this creates isotopes. Isotopes are atoms of the same element, yet they have different numbers of neutrons and subsequently different atomic masses. Many isotopes are found in nature; however usually there is a single isotope that is the most stable combination of neutrons and protons, and hence more common. Elements may have one or more isotopes that are radioactive, while other isotopes are stable. The isotopes of different elements differ in their atomic mass. The mass of the element that is presented on the periodic table is the average atomic mass. This utilizes the percent abundance of each isotope to calculate a value for most amounts of each element. Background Information The term isotope was suggested to Frederick Soddy by Margaret Todd. It derived from isos, which is Greek for "equal", and 2 / 6

3 topos, which is Greek for "place." In Soddy's eyes this was because even though these atoms have different atomic masses they should occupy the same place in the periodic table. Real World Application Discover processes or disciplines in the natural or man-made worlds that employ the concept. Atomic mass is most affected by the number of protons and neutrons an atom contains. Isotopes generally have a mass equal to almost exactly the addition of their neutrons and protons. Carbon-12, which has 6 protons and 6 neutrons, has an atomic mass of exactly Because of this unique trait carbon-12 is used as a reference mass when calculating atomic mass. In order to calculate atomic mass, the mass of all isotopes must be multiplied by their abundance and then added together. This will give the average mass of the element. For elements that have no stable isotopes, the mass of the most stable isotope is given as the atomic mass. Isotopes are used in a multitude of everyday objects. Smoke detectors, for instance, often contain a small amount of americium-241. One of the radioactive properties of this material allows for smoke to be detected at an extremely early stage. Another rising use for radioactive isotopes is food irradiation. This is a process where food is exposed to the radiation of an element, often cobalt-60, though not in direct contact with it. With the high energy particles that are passing through the food, bacteria and microorganisms are killed. Cellular processes that lead to over-ripening and spoiling are also hindered. Carbon, the main element in organic materials, has a variety of isotopes that are present in living organisms. By analyzing the abundances of these carbon molecules, paleontologists are able to discover the age of organic materials from bones to clothing. 3 / 6

4 - A hydrogen atom usually contains only one proton in its nucleus, however deuterium, an isotope of Vocabulary Learn important vocabulary for this concept, including words that might appear in assessments (tests, quizzes, homework, etc.) that indicate the use of this concept. Important Vocabulary Term Context Isotope Mass Spectroscopy - An accurate way to measure the mass of different isotopes is through mass spectroscopy. Neutron - Neutrons exhibit no charge, but have a similar mass to a proton. Radioactivity - Lead is a common element used to protect scientists and civilians against radioactivity. Videos Browse relevant videos from the Journal of Chemical Education's (JCE) Chemistry Comes Alive! library and other video sources. Ice Cubes in Water H 2 O (s), or ice, is placed into liquid water and floats. Heavy Water Ice Cubes D 2 O (s), or heavy ice, is put into water and sinks. Carbon Dating Explanation A short description of how Carbon dating is carried out, as well as one of its uses. 4 / 6

5 Summary Read a summary of the concept, indicating the enduring understanding students should retain after class. Summary Almost all elements have isotopes, atoms with a different number of neutrons but the same number of protons. They are often unstable but have specific uses in modern technology. Sample Problems Explore sample problems from the JCE QBank and other sources. Sample Problems Works Cited Review the works cited to write the researched parts of this page, such as the discover's biographical information and other areas. Works Cited [LINK URL: [LINK URL: [LINK URL: 5 / 6

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