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Is a element whose common isotopic form is the basis of the atomic mass unit?
Wiki User
∙ 11y ago
In the modern Periodic Table, an atom of the isotope carbon-12 has a mass of exactly 12.0000 dalton.Until around 1970 the basis was oxygen (natural mixture of isotopes) = 16.000 dalton, but by then the inconvenience of the fact that the "natural" mixture of isotopes was somewhat variable had made this concept rather difficult to work with, and the benefits of working with a defined isotope had been recognized. Carbon-12 had a mass very close to 12 on the old scale, so its adoption as the basis meant that the older tables of Atomic Mass could be used without modification.
Wiki User
∙ 11y ago
Wiki User
∙ 11y agoIt's not just an element, it's a particular isotope of a particular element.
The currently accepted standard is carbon-12, which by definition has a mass of precisely 12 atomic mass units when at rest, isolated, and in its nuclear and electronic ground states.
Before 1961, the scale was based on oxygen instead, but since this standard came into being before isotopes were known, it was a bit confusing:
Before 1929, or before 1961 if you were a chemist, an atomic mass unit was 1/16 of the isotopically weighted average mass of an oxygen atom.
However, if you were a physicist, between 1929 and 1961 an atomic mass unit was 1/16 the mass of an oxygen-16 atom.
The two definitions differed by about 0.03% - not a lot, but enough to show up in high precision work, which is the reason for the 1961 redefinition.
(Originally, the mass of hydrogen was used as the standard. I can't find any information on precisely when the switch to oxygen took place, but it would almost certainly have been after 1875.)
Wiki User
∙ 14y agoCarbon Atomic mass unit (u) is one twelfth of the mass of an isolated atom of carbon-12 (12C) at rest and in its ground state.
Wiki User
∙ 13y agoCarbon-12.
One Carbon-12 atom is given a relative mass of 12, so a single atomic mass unit is 1/12th the mass of a carbon-12 atom.
Wiki User
∙ 15y agoCarbon-12
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∙ 12y agoCarbon
Wiki User
∙ 11y agoCarbon (C)
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Why was basis of classification of element in the periodic table changed from atomic mass to atomic number?
Mendeleev's periodic table was based on the atomic masses of elements. However, this was not effective when isotopes were discovered. An isotope of an element is defined as the element having the same atomic number but varying mass numbers. So, mass numbers weren't constant and hence, a better characteristic was chosen -atomic number. Atomic number of any element was a characteristic of a particular element. Hence atomic numbers were taken as the basis of classification instead of atomic masses.
Can the atomic number of an particular element ever change?
No, the atomic number of an element can't change. Because, we can identify an element by its atomic number and atomic mass. and hence they have been arranged in the periodic table on the basis of their mass number and atomic mass so , it couldn't be changed. Every element has a fixed atomic number..
How is moseleys basis for arranging the elements different from mendelees?
Moseley's basis and Mendeleev's basis both involved experimental measurements. But Moseley's involved X-ray properties, and X-rays were not discovered when Mendeleev first stated the Periodic Law. Atomic weight and atomic number follow nearly the same sequence, but there are three cases of reversal of order: Argon element 18 atomic weight 40.0; potassium element 19 atomic weight 39.1. (Argon was not discovered until 1894; first periodic table 1869). Cobalt element 27 atomic weight 58.9; nickel element 28 atomic weight 58.7. (Very small difference; Mendeleev gave these two elements identical atomic weights) Tellurium element 52 atomic weight 127.6; iodine element 53 atomic weight 126.9 (Major problem for Mendeleev -- he insisted that the atomic weight of tellurium had to be 125, but careful re-measurements continued to show 127.5-128) Moseley's atomic number is definitely a better basis for the periodic law than Mendeleev's original suggestion of atomic weight.
Early attempts at organizing the element arranged them according to?
properties of the elements and atomic masses
Why is atomic number the proper basis for classification of elements?
Because Atomic number is the identity of an element , all the atoms of an element have the same atomic number while their mass numbers ma be different. for Example Argon(Ar) a noble gas and Calcium(Ca) an active metal have the same mass number 40.
Why was basis of classification of element in the periodic table changed from atomic mass to atomic number?
Mendeleev's periodic table was based on the atomic masses of elements. However, this was not effective when isotopes were discovered. An isotope of an element is defined as the element having the same atomic number but varying mass numbers. So, mass numbers weren't constant and hence, a better characteristic was chosen -atomic number. Atomic number of any element was a characteristic of a particular element. Hence atomic numbers were taken as the basis of classification instead of atomic masses.
John Dalton's atomic theory stated that atoms of the same?
According to John Dalton, all the atoms of a single element will have the same mass. This is the basis for the modern atomic theory.
Can the atomic number of an particular element ever change?
No, the atomic number of an element can't change. Because, we can identify an element by its atomic number and atomic mass. and hence they have been arranged in the periodic table on the basis of their mass number and atomic mass so , it couldn't be changed. Every element has a fixed atomic number..
How is moseleys basis for arranging the elements different from mendelees?
Moseley's basis and Mendeleev's basis both involved experimental measurements. But Moseley's involved X-ray properties, and X-rays were not discovered when Mendeleev first stated the Periodic Law. Atomic weight and atomic number follow nearly the same sequence, but there are three cases of reversal of order: Argon element 18 atomic weight 40.0; potassium element 19 atomic weight 39.1. (Argon was not discovered until 1894; first periodic table 1869). Cobalt element 27 atomic weight 58.9; nickel element 28 atomic weight 58.7. (Very small difference; Mendeleev gave these two elements identical atomic weights) Tellurium element 52 atomic weight 127.6; iodine element 53 atomic weight 126.9 (Major problem for Mendeleev -- he insisted that the atomic weight of tellurium had to be 125, but careful re-measurements continued to show 127.5-128) Moseley's atomic number is definitely a better basis for the periodic law than Mendeleev's original suggestion of atomic weight.
What property is used to arrange element on the periodic table?
Atomic number on the basis of Modern periodic law as on the view of Henry Mosely
Early attempts at organizing the element arranged them according to?
properties of the elements and atomic masses
Why is atomic number the proper basis for classification of elements?
Because Atomic number is the identity of an element , all the atoms of an element have the same atomic number while their mass numbers ma be different. for Example Argon(Ar) a noble gas and Calcium(Ca) an active metal have the same mass number 40.
Why are the numbers ordered as they are on the periodic table?
The numbers of the elements on the periodic table correspond to the number of protons the element has. For example, Oxygen has atomic nuber 8, which means it has 8 protons.
How did Henry Moseley revise mendeleevs periodic table?
In 1914 Henry Moseley found a relationship between an element's X-ray wavelength and its atomic number (Z), and therefore rearranged the table by nuclear charge / atomic number rather than atomic weight. Before this discovery, atomic numbers were just sequential numbers based on an element's atomic weight. Moseley's discovery showed that atomic numbers had an experimentally measurable basis.
When did mosley create his periodic table?
1914. In 1914 Henry Moseley found a relationship between an element's X-ray wavelength and its atomic number (Z), and therefore resequenced the table by nuclear charge rather than atomic weight. Before this discovery, atomic numbers were just sequential numbers based on an element's atomic weight. Moseley's discovery showed that atomic numbers had an experimentally measurable basis.
How did Henry Moseley affect the development of the periodic table?
He discovered that each element has its own atomic number.In 1914 Henry Moseley found a relationship between an element's X-ray wavelength and its atomic number (Z), and therefore resequenced the table by nuclear charge rather than atomic weight. Before this discovery, atomic numbers were just sequential numbers based on an element's atomic weight. Moseley's discovery showed that atomic numbers had an experimentally measurable basis.
What discovery did Henry Moseley lead him to reorganize the periodic table?
In 1914 Henry Moseley found a relationship between an element's X-ray wavelength and its atomic number (Z), and therefore resequenced the table by nuclear charge rather than atomic weight. Before this discovery, atomic numbers were just sequential numbers based on an element's atomic weight. Moseley's discovery showed that atomic numbers had an experimentally measurable basis.
