The International
Union of Pure and Applied Chemistry and the US
Geological Survey, announced the change after new research measured the
average mass of atoms more accurately.
Among those to have had their standard atomic weights adjusted are elements
like aluminium, fluorine, arsenic, caesium, cadmium and selenium.
The changes have occurred due to a greater understanding of the prevalence of
different versions of the atoms, known as isotopes.
Each isotope of an atom has a slightly different mass due to the number of
neutrons it contains.
The standard atomic weight is then calculated by taking into account the
abundance of each isotope to give an average weight for an atom.
These are then displayed on the Periodic Table that appears in text books
around the world.
Improved measurements and better data on the proportions of different atomic isotopes meant that nineteen of the atoms in the periodic table needed to be reassessed.
While some of the atoms were found to have an average weight that was a tiny fraction greater than previously calculated, others decreased.
The changes mean the total weight displayed on a Periodic Table has increased by 0.003640021, although clumped the changes together in this way means very little.
As atomic weights are relative they do not carry units.
In reality the tweaks to the standard atomic weight are unlikely to result in any fundamental changes in science and their main value lies purely from an academic point of view.
Only the most detailed of textbooks are likely to have to change the values, with atoms like thorium gaining just 0.000322 in weight.
Cadmium, however, has lost 0.0026 of weight in the reassessment. Gold was also reassessed but it was found to have the same atomic weight as before.
However, more accurate measurements of the different isotopes that were used to calculate the atomic weights could become useful for helping scientists date archaeological findings and trace materials in forensic investigations, for example.
Juris Meija, secretary of the IUPAC Commission on Isotopic Abundances and Atomic Weights, said: "The changes in the atomic weights are tiny.
"For many elements the atomic weights actually vary slightly in nature. This is because the proportion of the light and heavy isotopes of those elements is different from place to place.
"On a more precise scale, there are implications in science. Knowledge of atomic masses are important to understand the laws of physics.
"A good recent example of that was in 2005 when high-precision measurements of atomic masses allowed researchers to test the validity of the iconic E=mc2."
The IUPAC Commission on Isotopic Abundances and Atomic Weights meets every two years to reassess the atomic weights in the periodic table.
The use of Standard Atomic Weight has, however, been a controversial topic over the years due to confusion over how it was defined and what the term means.
However, they now define it as: “An atomic weight (relative atomic mass) of an element from a specified source is the ratio of the average mass per atom of the element to 1/12 of the mass of an atom of 12C.”
In recent years several new elements have also been added to the Periodic Table.
A spokesman for the International Union of Pure and Applied Chemistry said: “The importance of determining precise atomic weights has long been recognised, resulting in the creation of the International Atomic Weights Committee in 1899.
“IUPAC has overseen the periodic evaluation and dissemination of standard atomic-weight values since its formation in 1919.
“These changes in the standard atomic weights will be published in a new ‘Table of Standard Atomic Weights 2013’.”
The elements that have gained weight
Aluminium (Al): from 26.981 5386 to 26.981 5385 (+0.0000001)
Beryllium (Be): from 9.012 182 to 9.012 1831 (+0.0000011)
Cadmium (Cd): from 112.411 to 112.414 (+0.003)
Caesium (Cs): from 132.905 4519 to 132.905 451 96 (+0.00000006)
Thulium (Tm): from 168.934 21 to 168.934 22 (+0.00001)
Holmium (Ho): from 164.930 32 to 164.930 33 (+0.00001)
Praseodymium (Pr): from 140.907 65 to 140.907 66 (+0.00001)
Selenium (Se): from 78.96 to 78.971 (+0.011)
The elements that have lost weight
Arsenic (As): from 74.921 60 to 74.921 595 (-0.000005)
Cobalt (Co): from 58.933 195 to 58.933 194 (-0.000001)
Fluorine (F): from 18.998 4032 to 18.998 403 163 (-0.000000037)
Manganese (Mn): from 54.938 045 to 54.938 044 (-0.000001)
Molybdenum (Mo): from 95.96 to 95.95 (-0.01)
Niobium (Nb): from 92.906 38 to 92.906 37 (-0.00001)
Phosphorus (P): from 30.973 762 to 30.973 761 998 (-0.000000002)
Scandium (Sc): from 44.955 912 to 44.955 908 (-0.000004)
Thorium (Th): from 232.038 06 to 232.0377 (-0.00036)
Yttrium (Y): from 88.905 85 to 88.905 84 (-0.00001)
And the one that did not change
Gold (Au): from 196.966 569 to 196.966 569 (0)
Source: http://www.telegraph.co.uk/science/science-news/10333341/The-Periodic-Table-puts-on-weight.html
Improved measurements and better data on the proportions of different atomic isotopes meant that nineteen of the atoms in the periodic table needed to be reassessed.
While some of the atoms were found to have an average weight that was a tiny fraction greater than previously calculated, others decreased.
The changes mean the total weight displayed on a Periodic Table has increased by 0.003640021, although clumped the changes together in this way means very little.
As atomic weights are relative they do not carry units.
In reality the tweaks to the standard atomic weight are unlikely to result in any fundamental changes in science and their main value lies purely from an academic point of view.
Only the most detailed of textbooks are likely to have to change the values, with atoms like thorium gaining just 0.000322 in weight.
Cadmium, however, has lost 0.0026 of weight in the reassessment. Gold was also reassessed but it was found to have the same atomic weight as before.
However, more accurate measurements of the different isotopes that were used to calculate the atomic weights could become useful for helping scientists date archaeological findings and trace materials in forensic investigations, for example.
Juris Meija, secretary of the IUPAC Commission on Isotopic Abundances and Atomic Weights, said: "The changes in the atomic weights are tiny.
"For many elements the atomic weights actually vary slightly in nature. This is because the proportion of the light and heavy isotopes of those elements is different from place to place.
"On a more precise scale, there are implications in science. Knowledge of atomic masses are important to understand the laws of physics.
"A good recent example of that was in 2005 when high-precision measurements of atomic masses allowed researchers to test the validity of the iconic E=mc2."
The IUPAC Commission on Isotopic Abundances and Atomic Weights meets every two years to reassess the atomic weights in the periodic table.
The use of Standard Atomic Weight has, however, been a controversial topic over the years due to confusion over how it was defined and what the term means.
However, they now define it as: “An atomic weight (relative atomic mass) of an element from a specified source is the ratio of the average mass per atom of the element to 1/12 of the mass of an atom of 12C.”
In recent years several new elements have also been added to the Periodic Table.
A spokesman for the International Union of Pure and Applied Chemistry said: “The importance of determining precise atomic weights has long been recognised, resulting in the creation of the International Atomic Weights Committee in 1899.
“IUPAC has overseen the periodic evaluation and dissemination of standard atomic-weight values since its formation in 1919.
“These changes in the standard atomic weights will be published in a new ‘Table of Standard Atomic Weights 2013’.”
The elements that have gained weight
Aluminium (Al): from 26.981 5386 to 26.981 5385 (+0.0000001)
Beryllium (Be): from 9.012 182 to 9.012 1831 (+0.0000011)
Cadmium (Cd): from 112.411 to 112.414 (+0.003)
Caesium (Cs): from 132.905 4519 to 132.905 451 96 (+0.00000006)
Thulium (Tm): from 168.934 21 to 168.934 22 (+0.00001)
Holmium (Ho): from 164.930 32 to 164.930 33 (+0.00001)
Praseodymium (Pr): from 140.907 65 to 140.907 66 (+0.00001)
Selenium (Se): from 78.96 to 78.971 (+0.011)
The elements that have lost weight
Arsenic (As): from 74.921 60 to 74.921 595 (-0.000005)
Cobalt (Co): from 58.933 195 to 58.933 194 (-0.000001)
Fluorine (F): from 18.998 4032 to 18.998 403 163 (-0.000000037)
Manganese (Mn): from 54.938 045 to 54.938 044 (-0.000001)
Molybdenum (Mo): from 95.96 to 95.95 (-0.01)
Niobium (Nb): from 92.906 38 to 92.906 37 (-0.00001)
Phosphorus (P): from 30.973 762 to 30.973 761 998 (-0.000000002)
Scandium (Sc): from 44.955 912 to 44.955 908 (-0.000004)
Thorium (Th): from 232.038 06 to 232.0377 (-0.00036)
Yttrium (Y): from 88.905 85 to 88.905 84 (-0.00001)
And the one that did not change
Gold (Au): from 196.966 569 to 196.966 569 (0)
Source: http://www.telegraph.co.uk/science/science-news/10333341/The-Periodic-Table-puts-on-weight.html
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