What is bohrs law?please can you teach me how calculate relative atomic mass

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jwuenschel eNotes educator| Certified Educator

I'm guessing you are referring to Bohr's model as Bohr's law.  Bohr's law states, "The crazier the theory, the more likely it is to be correct."  It is attributed to the same scientists that is came up with Bohr's model, Neils Bohr.  The Bohr model refers to atoms in a simplistic manner.  Each atom is depicted much the same as we view our solar system with the sun at the center and the planets orbiting it.  In the case of the atom, we have a positively charged nucleus made up of protons and neutrons being orbited by negatively charged electrons.

Calculating relative atomic mass is not difficult.  Relative atomic mass is defined as "the weighted average of the masses of the isotopes relative to 1/12 of the mass of a carbon-12 atom."  Basically, you are calculating a weighted average.  Let's suppose you have some element "A" that has two isotopes (Isotope: atoms having the same number of protons but different numbers of neutrons.) A-11 and A-17(11 and 17 are the atomic numbers of each isotope).  Further suppose that in any random sample of 100 atoms of element A you find 60 atoms of A-11 and 40 atoms of A-17.  To calculate the relative atomic mass you would simply do the following:

1.multiply each isotope's atomic number by the number of atoms of each

2.add the products

3. divide the sum of the products by the total number of atoms

((11 x 60) + (17 x 40))/100 = 13.4

13.4 is the relative atomic mass of element A