Nuclear symbols Na 23 11 Mass number =? Atomic number =? p + n p ( = e - ) p? e-?e-? n? 11 12
What are isotopes? Cl 35 17 Cl 37 17 p? e-?e-? n? p? e-?e-? n? 17 1820 17 Atoms of the same element with: The same atomic number but different mass numbers Same number of protons but different numbers of neutrons
Why is 35 Cl O.K.? Cl 35 17 Cl 37 17 Relative isotopic mass Cl-35 Cl-37 Chlorine always has an atomic number of 17!
So what is relative atomic mass? Cl-35 Cl-37 75% 25%
Relative atomic mass is the average of the relative isotopic masses Cl-35 Cl-37 75% 25% How do we get a relative atomic mass of 35.5?
What 2 things did we need to know? Relative isotopic masses. The relative abundances.
How do we find them out? Use a mass spectromete r