Average Atomic Mass

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Average Atomic Mass : 

Average Atomic Mass Most of the atom’s mass comes from the nucleus When measuring the mass of a single atom, we use the units u (atomic mass unit). 1 u = 1/12 the mass of a single Carbon-12 atom

Why aren’t the masses on the Periodic Table whole numbers? : 

Why aren’t the masses on the Periodic Table whole numbers? The atomic masses on the Periodic Table are average masses for all of the isotopes of that element. Isotopes – atoms of the same element that differ only in their mass The abundance of each isotope is determined with an instrument known as a mass spectrometer.

Slide 3: 

In a given sample of chlorine… 75.78% is Chlorine-35 24.22% is Chlorine-37 To calculate the average atomic mass, multiply each isotope’s mass by its relative abundance. Then add these up. 0.7578 x 35 u = 0.2422 x 37 u = 26.52 u 8.961 u 35.481u = 35.48u