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: FLASHBACK: Protons are what animal? Protons are what animal? Neutrons are what animal? Neutrons are what animal? Electrons are what animal? Electrons are what animal? Mass # = mass of the nucleus Mass # = mass of the nucleus Nucleus = protons + neutrons Nucleus = protons + neutrons Therefore: Therefore: mass# = protons + neutrons

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

5. Practice  Carbon – 12 2. 2. p+p+p+p+ e-e-e-e- n0n0n0n0 Mass # 17 8 p+p+p+p+ e-e-e-e- n0n0n0n0 Draw Diagram 6 6 6 12 8 8 9 17 O Oxygen - 17 12 6 C 6 9

6. Calculating Atomic Mass Atomic Mass is the average of all an element’s masses Atomic Mass is the average of all an element’s masses You need two values You need two values Mass of each isotope Mass of each isotope % abundance of each isotope % abundance of each isotope Percent abundance is how much of the isotope is represented in the world 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 For element X mass = 7.016 abundance = 92.5% 7

8. Atomic Mass Chart Isotope Mass (amu) % Abundance X - 66.0157.50 X - 77.01692.5 x x 45.1 649 + 694 100 = 6.94 amu

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