Isotopes and Mass Number

1. Isotopes and Mass Number

2. Isotope Atoms of the same element with: Same number of protons BUT Different number of neutrons ELEMENT IS TO ISOTOPE AS DOG IS TO DOG BREED

3. Mass Number: Mass of an atom • FLASHBACK: • Protons are what animal? • Neutrons are what animal? • Electrons are what animal? • Mass # = mass of the nucleus • Nucleus = protons + neutrons • Therefore: mass# = protons + neutrons

4. Nomenclature Carbon - 14 Mass Number C 14 6 Atomic Number

5. Practice Draw Diagram • Carbon – 12 C 12 6 6 6 6 6 12 Oxygen - 17 8 O 17 8 8 9 17 9

6. Calculating Atomic Mass • Atomic Mass is the average of all an element’s masses • You need two values • Mass of each isotope • % abundance of each isotope • Percent abundance is how much of the isotope is represented in the world

7. Example: The following is data for the unknown element X. For element X mass = 6.015 abundance = 7.50% 6 7 For element X mass = 7.016 abundance = 92.5%

8. Atomic Mass Chart X - 6 6.015 7.50 45.1 x X - 7 7.016 x 92.5 649 + 694 6.94 amu = 100

9. Find the atomic mass on the periodic table What is element X? 6.94 amu The element is Lithium!