Tuesday, July 17, 2012

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Atomic number and mass

Atomic number
The number of proton present in the nucleus of an atom of an element is called its atomic number. As the number of protons is equal to the number of electrons,the atomic number is also defined as the number of electrons present in an atom.


    Atomic number= Number of protons= Number of electrons


Each element has its own atomic number.


Atomic mass
The mass of electron is very small so it can't be calculated.The protons and nucleus are located at the nucleus. In practice,the mass of an atom is the sum of the masses of protons and nucleus in it. Thus,the sum of protons and neutrons is called atomic mass.It is also called atomic weight.



    Atomic mass= Number of protons+ Number of neutrons



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