1. Lesson 24: Isotopes An element can be identified by the # of protons it has # of neutrons can vary Neutrons add to the mass of the atom, but do not change the element’s identity

2. Lesson 24: Isotopes Potassium-37Potassium-42 Mass Number 3742 # of protons 19 # of neutrons

3. Lesson 24: Isotopes Potassium-37Potassium-42 Mass Number 3742 # of protons 19 # of neutrons 1823

4. Lesson 24: Isotopes Potassium-37 and Potassium-42 are isotopes of potassium Isotopes have the same # of protons, but different masses and different # of neutrons

5. Lesson 24: Isotopes U-233U-235U-238 Mass Number # of protons # of neutrons

6. Lesson 24: Isotopes U-233U-235U-238 Mass Number 233235238 # of protons 92 # of neutrons 141143146

7. On the Periodic Table they do NOT list all the isotopes for each element. Instead they calculate the average of the isotopes masses, this is called: ATOMIC WEIGHT Use the Periodic Table, find the Atomic Weights for the following: CONaCl

8. How to calculate ATOMIC WEIGHT: (mass*decimal %) + (mass*decimal%)… = Ex. In the world, 75.53% of the chlorine is chlorine-35. In the world, 24.47% of the chlorine is chlorine-37. (35 * 0.7553) + (37 * 0.2447) = 35.45 so the atomic weight of chlorine’s isotopes is 35.45 amu