The International Union of Pure and Applied Chemistry decided to change the atomic weight of ten common elements - instead of number one there will be different values under different conditions
For the first time in history, there will be changes in the atomic weight of some of the elements listed in the periodic table of the chemical elements, the well-known table displayed on the walls of chemistry classrooms and on the covers of chemistry books all over the world.
In the new table, which appears in the announcement published this month, the atomic weights of ten elements - hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine and thallium - will appear in a new format that will more accurately reflect the appearance of the elements in nature.
"Over a hundred and fifty years ago, many people learned to use the normal atomic weights - individual values - found on the inside cover of books for studying chemistry and on the periodic table of the elements. With the advancement of technology, we discovered that the numbers in the table are not as static as we previously thought," says Dr. Michael Wieser, a professor at the University of Calgary, Canada, who also serves as secretary of the Committee on Isotope Distribution and Atomic Weights at the International Union of Pure and Applied Chemistry (IUPAC). This organization oversees the evaluation and dissemination of information about atomic weight values.
Advanced analytical methods are able to measure the atomic weight of many of the elements accurately, and these small deviations in the atomic weight of the elements are important in research and industry. For example, accurate measurements of the distribution of carbon isotopes could be used to determine the cleanliness level and origin of food, such as vanilla and honey. Isotopic measurements of nitrogen, chlorine, and other elements are used to monitor pollutants in streams and groundwater. In sports drug testing, performance-enhancing hormones, such as testosterone, are detectable in the human body since the atomic weight of natural testosterone in humans is slightly higher than synthetic testosterone.
The atomic weights of these ten elements will henceforth be expressed as intervals with an upper limit and a lower limit, which more accurately reflects these small deviations in atomic weight. These changes were published in an official announcement by the organization.
For example, it is accepted that the sulfur atom has an atomic weight of 32.065. However, its practical atomic weight may be any weight between the value 32.059 and the value 32.076, depending on the source of the element's presence. "In other words, knowing the exact atomic weight can be used to decipher the origins and history of a certain element in nature," says the researcher.
Elements with a single stable isotope do not exhibit deviations in their atomic weights. For example, the normal atomic weights of fluorine, aluminum, sodium, and gold are constant, and their values are known to an accuracy of more than six decimal places.
"Although this change provides many advantages in understanding chemistry, you can imagine the challenge now facing teachers and students who will have to choose a single value from a list of values when they come to perform chemistry calculations," says one of the committee partners. "We hope that chemists and chemistry teachers will treat this challenge as a unique opportunity to encourage the interest of young students in chemistry and generate enthusiasm for the creative future of chemistry."
The University of Calgary has contributed, and continues to contribute greatly to the study of atomic weight deviations. Professor H. Roy Krouse founded the Stable Isotope Laboratory in the Department of Physics and Astronomy in 1971. His earlier research established the wide natural range of atomic weights of important elements, including carbon and sulfur. Today, university researchers in the fields of physics, environmental science, chemistry and geology use deviations in atomic weight values to trace the origins of meteorites, to determine the sources of pollutants found in air and water, and to study the trajectory of carbon dioxide gas in a geological medium. This significant change in the presentation of the atomic weights is based on work conducted between 2010-1985 which was funded by IUPAC, the University of Calgary and other members and institutions represented on the committee.
It was decided that the year 2011 will be the International Year of Chemistry, in which the changes in the table of atomic weights of the elements will be presented, as part of the activities dedicated to this year.
The official news from the organization
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Arya, I was also disappointed by the title "Revolutionary", to put it mildly. Not even a change such as the introduction of newly discovered unstable elements (not that this is a revolutionary discovery anymore...), but more detail instead of the weighted value that was presented until now...
Let's hope that there will be more "exciting" and interesting articles in chemistry in the future.
"Revolutionary change" - define revolutionary... I was already expecting to see innovations on the structure of the universe. This is a minor change to my non-chemical impression. False title.
Oren, thanks for the clarification. I have no knowledge of chemistry except for memories from decades ago of what we learned a little in high school. So I understand that in general I was right and the only thing I was wrong about was that I thought that the common weight appears in the table and in fact the weighted one appears.
Aria, a small mistake in your previous knowledge. Isotopes are elements that have the same atomic number (same number of protons) but different atomic mass (different number of neutrons), when the electron mass is neglected. It is customary to consider the common element (as opposed to its isotopes) as an atom with the same amount of neutrons as protons, and indeed it is usually the most common, but this is not always the case, especially in the light elements. In hydrogen, the most common atom has one proton and no neutrons.
Therefore, it was decided that in the periodic table the weighted value is presented (according to the degree of distribution of all isotopes in nature) - and not the most common element as you thought. Indeed, sometimes the other isotopes are so common that their influence on the atomic weight is almost unnoticeable.
Their proposal is, in my opinion, to specify for the elements for each isotope (or at least the common ones among them) their distribution and weight separately. So we will not use the weighted weight calculations (unless otherwise known) but will adjust the calculations according to the uses and the source of the atom (for example for hydrogen).
Indeed, for every student, engineer and chemist, this will not make much difference, apart from the lack of need to look for the information in the literature and accessibility to the information in the periodic table. But for high school students this will be a more complete understanding of the world of chemistry. I believe they hope this will wink more students studying chemistry in high school for example to see the more applied world of chemistry (beyond better understanding) and attract them to this field.
The chemist gentlemen will teach me. If I understood correctly - the variation of the atomic weight is due to different mixtures of isotopes. After all, it was always known that isotopes have different atomic weights. So in the past they put in a table the atomic weight of the most common isotope (which is also the most stable? If there is instability) right? If I'm right then all they did was decide to list the range which is basically everything between the heaviest and the lightest atomic weight. This is not actually an exciting innovation but just a listing in the table of the range for convenience. And all the applications resulting from the knowledge of the range, for example the knowledge of the source of the element as explained in the article - could have been carried out even before that, even if it was not listed in the table, because the information existed. Am I right?