Why any atom of an element is divided by 1/12th of carbon atom to find out the atomic mass of that same element
I assume you mean as the definition of an atomic unit. Since protons and neutrons have slightly different weights, and average of the two is used to determine an atomic unit. Carbon-12 is the most common and readily available isotope to have exactly the same number of protons and neutrons, 6 of each, and thus provides a perfect average when divided by the total number of protons and neutrons. (Carbon-12 also has 6 electrons, but the mass of an electron is so small as to be considered negligible). Dividing by 12 allows even the smallest atom, hydrogen, to have a mass that is a whole number, rather than a fraction.
There are several atoms smaller than carbon-12 with the same number of protons and neutrons, (for example, dueterium, the hydrogen isotope present in heavy water), but they are much less common. By setting the most common isotope of carbon as the standard, it insures that it is readily available to anyone who needs access to it
the usage of 1/12 of a carbon is a convention that had been adopted quite a long time back.
It is based on the fact that the carbon-12 atom has 6 protons, 6 neutrons and 6 electrons. Of these the 6 electrons have negligible weight compared to the others (1 electron is around 1/1836 times as heavy as a proton). Protons and neutrons weigh almost the same at least at the accuracy levels during the time when the convention was adopted.
Hence 1 proton weighs equal to 1 neutron = 1/12 of a carbon-12 atom which has 6 protons and 6 neutrons.
And as the weight of all atoms is almost completely from the contained protons and neutrons, it is mentioned in terms of 1/12 carbon-12 atom.
So for example, oxygen has 8 protons and 8 neutrons, the weight of oxygen is approximately (8+8)*1/12 of carbon-12 atom.
I assume you mean as the definition of an atomic unit. Since protons and neutrons have slightly different weights, and average of the two is used to determine an atomic unit. Carbon-12 is the most common and readily available isotope to have exactly the same number of protons and neutrons, 6 of each, and thus provides a perfect average when divided by the total number of protons and neutrons. (Carbon-12 also has 6 electrons, but the mass of an electron is so small as to be considered negligible). Dividing by 12 allows even the smallest atom, hydrogen, to have a mass that is a whole number, rather than a fraction.
There are several atoms smaller than carbon-12 with the same number of protons and neutrons, (for example, dueterium, the hydrogen isotope present in heavy water), but they are much less common. By setting the most common isotope of carbon as the standard, it insures that it is readily available to anyone who needs access to it
the usage of 1/12 of a carbon is a convention that had been adopted quite a long time back.
It is based on the fact that the carbon-12 atom has 6 protons, 6 neutrons and 6 electrons. Of these the 6 electrons have negligible weight compared to the others (1 electron is around 1/1836 times as heavy as a proton). Protons and neutrons weigh almost the same at least at the accuracy levels during the time when the convention was adopted.
Hence 1 proton weighs equal to 1 neutron = 1/12 of a carbon-12 atom which has 6 protons and 6 neutrons.
And as the weight of all atoms is almost completely from the contained protons and neutrons, it is mentioned in terms of 1/12 carbon-12 atom.
So for example, oxygen has 8 protons and 8 neutrons, the weight of oxygen is approximately (8+8)*1/12 of carbon-12 atom.
