Atomic weight carbon-12 standard

Its atomic weight was used as a standard of comparison for each of the other elements until 1961 when the International Union of Pure and Applied Chemistry adopted carbon 12 as the new basis. 

Atomic Weights of the Elements Based on the Carbon 12 Standard... 

C = 12 internationally adopted as the unified atomic weight standard by both chemi.sts and physicists. 6-coordinate carbon established in various carboranes by W. N. Lipscomb and others. (Nobel Prize 1976 for structure and bonding of boranes). 

At one time, the hydrogen atom with one proton and no neutron was used as the standard to define 1 atomic mass unit (1 amu). Today, chemists use carbon-12, the most abundant isotope of carbon for the standard amu, which is defined as 1/12 of the C-12 atom. Therefore, the actual atomic weight for an element is in average mass units (numbers), taking into account all the isotopes (atoms) of that element. 

Symbol Sn atomic number 50 atomic weight 118.69 a Group IV A (Group 14) metaUic element of carbon family electron configuration Kr] 4di°5s25p2 valence states +2, +4 atomic radius 1.41 A electronegativity 1.7 standard electrode potential, E° for Sn2+ -i- 2e Sn is -0.1375 V ten naturally-occurring sta-... 

Molecular Weight mwi) or atomic weight awi) is calculated from the molecular formula, using standard elemental molecular weights (carbon = 12.01). 

The density of ethylene at very low pressure corresponds to the ideal density 1.251223 g/l at standard conditions. The formula of ethylene is C2H4. Calculate from this information a precise value of the molecular weight of ethylene. Assuming the atomic weight of hydrogen to be 1.0080, calculate the atomic weight of carbon. 

To know more about molecular weights, one must first become familiar with the concept of atomic weights. Because an element (e.g., carbon, oxygen, sulfur, etc.) often exists as a mixture of two or more (stable and unstable forms) natural isotopes that have the same number of protons but differ in the number of neutrons, atomic masses of these isotopes are slightly different from each other. In this case, atomic masses are averaged and the ratio of the resultant value to some standard is defined as the atomic weight of the element. 

This value is carbon s atomic mass. Because an element s atomic mass is often described without units, carbon s atomic mass is usually described as 12.011 instead of 12.011 u. The atomic mass of any element is the weighted average of the masses of the naturally occurring isotopes of the element. (It is very common to call this property atomic weight, but because it describes the masses of the atoms, not their weights, this text will use the term atomic mass.) Scientists have calculated the atomic masses of all elements that have stable isotopes, and they can be found on any standard periodic table, including the table in this book. 

The mole (abbreviated mol) is defined as the amount of a substance comprising as many elementary units as there are atoms in 12 g of The definition of the mole is equivalent to the statement that the mass of one mole of a pure substance in grams is numerically equal to its molecular weight calculated from the standard table of atomic weights, in which the atomic weight of carbon is given as 12.01115. This number differs from 12 because it applies to the natural isotopic mixture of carbon rather than to pure... 

Radiometric dating is a method that scientists use to measure the age of things. The most widely known form of radiometric dating is that based on carbon-14. It works like this. Carbon-12 is the most common form of carbon, and carbon-14 is what is called an isotope of it. (An isotope is a variation of the normal atom of an element, in that it has more or less neutrons than the standard atom.) Carbon-12 has six protons and six neutrons at its nucleus, and is therefore said to have an atomic weight of 12. The component of an atom that determines its character is the number of electrons in orbit around its nucleus. In carbon s case there are six. 

The atomic weight of an element is the average weight of all the isotopic masses of the element, calculated on the basis of their relative abundance in nature. The atomic weights are set on a carbon-12 scale. This is the standard weight scale that is used worldwide to express atomic weights. Exploring this further, we can say that 12 atomic mass units (amu) make up the mass of one... 

In 1961, however, international organizations of both chemists and of physicists agreed to adopt an atomic weight standard based on carbon-12 set equal to exactly 12.0000. This new standard was almost exactly that of the old chemical atomic weights and yet it was tied to a single isotope and not to the average of a group of them. 

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