CHAPTER 2.2 modified - CHAPTER2.2 ATOMICNUMBER MASSNUMBER...

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CHAPTER 2.2  ATOMIC NUMBER,  MASS NUMBER &  ISOTOPES
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§ Represented by the letter Z. § The number of protons in the nucleus  of an atom.    Atomic Number A proton is one of the three basic "building  blocks" of the atom (along with the neutron  and electron). It is a subatomic particle with  a unit positive charge. (The unit of charge  is 1.602 x 10-19 coulomb.
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Represented by the letter A. The total number of protons and neutrons in the  atomic nucleus of an atom.    Mass Number + Number of neutrons Number of protons = Mass Number total number of nucleons in the atom's nucleus. Hydrogen has three natural isotopes: 1H, 2H, and 3H. Each isotope has a  different   mass number. 1 H has  1 proton . Its  mass number  is 1. 2H has 1 proton and 1 neutron. Its mass  number is 2. 3H has 1 proton and 2 neutrons. Its mass number is 3. 99.98% of all  hydrogen is 1H 0.018% of all hydrogen is 2H 0.002% of all hydrogen is 3H  Together, they give a value of atomic mass of hydrogen equal to 1.0079 g/mol. 
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It is not a whole number  because it is an average.  Atomic Masses are the  decimal numbers on the  periodic table .
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