Reminders & Daily Schedule

1. Reminders & Daily Schedule • Element Quiz #2 tomorrow • Atomic Structure Test Friday • Review Isotope/Different Element Worksheet • Remind 101 • Isotope Abundance/Average Atomic Mass Notes • Isotope Practice Packet

3. Isotopes: Average Atomic Mass & Abundance

4. Average Atomic Mass • The decimal number on periodic table • Weighted average of all isotopes of an element • Depends on percent (relative) abundance and mass of each isotope • Measured in “atomic mass units” (amu)

5. Example • Element X has two isotopes • #1: • Mass=6 amu • Relative Abundance= 7.5% • #2 • Mass=7 amu • Relative Abundance=92.5% • What element is it?

6. To solve example 1 Average atomic mass= [(mass #1)x(abundance #1)] + [(mass #2)x(abundance #2)] (6 x .075) + (7 x .925)= 0.45 + 6.475= 6.925 amu Closest to ? Lithium 6.94

7. Finding Percent Abundance There are two stable isotopes of Chlorine: Chlorine-35 (which weighs 34.97 amu) and Chlorine-37 (which weighs 36.97 amu). If the relative atomic mass of Chlorine is 35.45 amu, what is the percent abundance of each isotope?

8. Chlorine-35 (which weighs 34.97 amu) &Chlorine-37 (which weighs 36.97 amu). X • Cl-35= ? % • Cl-37= ? % Y ? • Having 2 variables would be much harder. • We want to express Cl-37 abundance using X .6 & .4 .8 & .2

9. Chlorine-35 (which weighs 34.97 amu) & Chlorine-37 (which weighs 36.97 amu). Chlorine relative atomic mass 35.45 amu. • Cl-35 = 34.97 amu • Cl-37 = 36.97 amu X • Cl-35= ? % • Cl-37= ? % 1-X 35.45 34.97 36.97 X 1-X (34.97X) + (36.97)-(36.97X) = 35.45 -2.00X + 36.97 = 35.45 -2.00X = -1.52 2.00X = 1.52 X= 1.52/2.00 X = 0.76

10. Chlorine-35 (which weighs 34.97 amu) & Chlorine-37 (which weighs 36.97 amu). Chlorine relative atomic mass 35.45 amu. • Cl-35 = X = .76 = 76% • Cl-37 = (1-X) = (1-.76) = .24 = 24%

11. Isotope Practice Packet • Turn in if finished today—if not it is homework due at the beginning of class tomorrow • Don’t forget to sign up for and tell your parents about remind 101