1. Isotopes

2. Nuclear Symbol
M ass He 4 2
A tomic
N umber

3. Hyphen Notation
Helium - 4

4. Isotopes Are…. Atoms w/ same # p+ but different # no
different mass # s
chemically alike- react the same way
b/c identical # of p+ & e-
Atomic Mass rounds to most abundant isotope

5. Atomic Mass Formula Mass (amu) x Abundance (%) = Relative Mass or
Then add up all the relative masses or
( Mass* % Abundance) + (Mass * %Abundance)+…

6. Example Cr-50= 4.31%; Cr-52= 83.76%; Cr-53=9.55%; Cr-54=2.38%
Chromium exists in 4 isotopic forms with the following abundances:
Cr-50= 4.31%; Cr-52= 83.76%; Cr-53=9.55%; Cr-54=2.38%
Calculate the average atomic mass of chromium.