2. Atomic Mass Standard mass unit is derived from carbon 12 Atomic mass unit – the mass equal to 1/12 the mass of one Carbon 12 atom

3. Atomic Mass Experiments show that H is 8.400% less massive than carbon 0.084 x 12.00 amu = 1.008 amu

4. Average atomic mass The number on the periodic table is based on the average of isotopes Carbon is labeled as 12.011 seems unlikely from above discussion Carbon comes in two main isotopes: 98.90% carbon 12 and 1.10% carbon 13 Mass of carbon 12 = 12.00000 amu carbon 13 = 13.00335 amu

5. Average atomic mass To get average (Percent/100) a x mass a + (Percent/100) b x mass b + …. For carbon (0.9890) (12.00000 amu) + (0.01110) ( 13.00335) = = 12.01

6. Problem Mg has three naturally occurring isotopes. Mg 24 (23.985 amu) with 78.99 % abundance, Mg 25 (24.986 amu) with 10.00% abundance, and a third will 11.01% abundance. Using the atomic mass of magnesium from the periodic table, calculate the mass of the third isotope.

7. Mass spectrometer

9. Mass Spec of Hexane

10. Different samples of Gold