Isotopes

1. Isotopes Average Atomic Masses

2. Atomic Number • The atomic number of an element is the number of protons in the nucleus. • The atomic number of an atom will never change. • If the number of protons in an atom changes, the atom no longer has the properties of that atom

3. Atomic Mass • The mass number is the total number of protons and neutrons in the nucleus. • That means that the mass number is the total number of protons plus the total number of neutrons.

4. Isotopes • Atoms that have different numbers of neutrons than other atoms of the same element. • All elements can be found as isotopes. • Examples • C12 C14 • He3 He4

5. Average Atomic Mass • weighted average of the atomic mass of an element’s isotopes • If you know the abundance of each isotope, you can calculate the average atomic mass of an element.

6. How to find Average Atomic Mass • The mass of a Cu-63 atom is 62.94 amu, and that of a Cu-65 atom is 64.93 amu. • Using the data below, find the average atomic mass of copper. • abundance of Cu-63 = 69.17% • abundance of Cu-65 = 30.83%

7. How to find Average Atomic Mass • The contribution of each isotope is equal to its atomic mass multiplied by the fraction of that isotope. • contribution of Cu-63: 62.94 amu × 0.6917 • contribution of Cu-65: 64.93 amu × 0.3083 • Average atomic mass is the sum of the individual contributions: • (62.94 amu × 0.6917) + (64.93 amu × 0.3083) • = 63.55 amu • Video Link

8. Assignment • Complete the Average Atomic Mass Worksheet • Quiz 4