Gold and Another 18 Elements Get a New Atomic Weight

Nineteen of chemical elements in the periodic labels (including gold, cadmium, arsenic, and aluminum) having atomic weight adjustment. The International Union of Pure and Applied Chemistry (IUPAC) announced the approval of a new weighting to all elements, thanks to the measurement and calculation of a particular isotope abundance is better and more accurate.

Standard atomic weight is the average mass of an element in atomic mass units. One Atomic Mass Unit (AMU) is equal to 1/12 the mass of one atom of carbon-12: One carbon atom is roughly equal to 5.857x10^-26 ounces.

To calculate the standard atomic weight of an element, the scientists calculate average atomic weight of all the stable isotopes. All atoms of an element have the same number of protons in the core, but the number of neutrons in the nucleus varies depending isotopes. This condition causes the difference in atomic weight. For example, carbon-12 has six protons and six neutrons. Slightly heavier from its cousin, carbon-13 which has six protons and seven neutrons.

"An abundance of isotopes in the Earth also varies. Growing number of isotopes, the more it will affect the average," wrote the scientists, as quoted by LiveScience, on Tuesday, October 1, 2013.

The IUPAC officials said the new calculations lead to changes in the abundance of this isotope weights for the element molybdenum, cadmium, selenium, and thorium. Weight changes selenium is vital for non-metallic chemical element has not been revised since 1934. "It does not happen often," said Juris Mejía, Secretary of the IUPAC Commission for isotopic abundance and atomic weight.

The classic Periodic Table organizes the chemical elements according to the number of protons that each has in its atomic nucleus. (Picture from: http://www.livescience.com/)

New weights of another 15 chemical elements are determined through a more accurate measurement. The change is also not too flashy. For an axample, atomic weight of Gold is updated from 196.966 569(4) AMU to 196.966 569(5) AMU. The numbers in parentheses represent the uncertainty in the last digits of the atomic weights.

Changes in chemical elements will be published in the "Table of Standard Atomic Weights 2013" in the Pure and Applied Chemistry 2014 journal. Mejía said that, although very small changes in the weight element but it brough practical implications for research.

"Knowledge of the atomic mass is very important to understand the laws of physics," he said. In 2005, a highly accurate atomic mass measurements were allows the researchers to test the validity of the law of relativity formula E=mc² is composed by Albert Einstein. Studies that rely on atomic masses of silicon and sulfur was published the Nature journal. *** [EKA | FROM VARIOUS SOURCES | LIVESCIENCE | MAHARDIKA SATRIA HADI | KORAN TEMPO 4361]

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Here are the details:

• Molybdenum: from 95.96(2) to 95.95(1) 
• Cadmium: from 112.411(8) to 112.414(4) 
• Selenium: from 78.96(3) to 78.971(8) 
• Thorium: from 232.038 06(2) to 232.0377(4) 
• Beryllium: from 9.012 182(3) to 9.012 1831(5) 
• Fluorine: from 18.998 4032(5) to 18.998 403 163(6) 
• Aluminum: from 26.981 5386(8) to 26.981 5385(7) 
• Phosphorus: from 30.973 762(2) to 30.973 761 998(5) 
• Scandium: from 44.955 912(6) to 44.955 908(5) 
• Manganese: from 54.938 045(5) to 54.938 044(3) 
• Cobalt: from 58.933 195(5) to 58.933 194(4) 
• Arsenic: from 74.921 60(2) to 74.921 595(6) 
• Yttrium: from 88.905 85(2) to 88.905 84(2) 
• Niobium: from 92.906 38(2) to 92.906 37(2) 
• Cesium: from 132.905 4519(2) to 132.905 451 96(6) 
• Praseodymium: from 140.907 65(2) to 140.907 66(2) 
• Holmium: from 164.930 32(2) to 164.930 33(2) 
• Thulium: from 168.934 21(2) to 168.934 22(2) 
• Gold: from 196.966 569(4) to 196.966 569(5)