What is atomic number

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All atoms of a particular element have the same number of protons in the nucleus .This number is a basic property of an element,called it atomic number (Z) .


        The atomic number (z) is the number of protons in the nucleus of an atom.


       Z = number of protons


For example : the hydrogen atom have one proton in the nucleus; and  uranium have 92 protons in the nucleus.So,


H atom  Z = 1


U atom Z = 92


 Mass  number : We characterize a nucleus by its atomic number (Z) and its mass number (A).The mass number (A) is the total number of protons and neutrons in a nucleus.


For example : sodium atom has number of protons 11 and number of neutrons 12 .So,


   Mass number of Na atom = number of protons + number of neutrons = 11 + 12 = 23 


 A nuclide is a particular nucleus characterized by a definite atomic number and mass number. The  shorthand notation for any nuclide consists of the symbol of the element with the atomic written as a subscript on the left and the mass number as a superscript on the left.