1. WHAT DO THESE BOXES MEAN?? Number of protons/ Atomic Number All atoms of the same element have the same number of protons

2. THE ATOM…THROUGH THE YEARS

4. IF WE MADE A SCALE MODEL OF AN ATOM AND WANTED TO USE COWBOY STADIUM AS OUR ELECTRON CLOUD, THE NUCLEUS OF THE ATOM WOULD BE THE SIZE OF THE ERASER ON THE END OF YOUR PENCIL. AN ELECTRON WOULD STILL BE SMALLER THAN THE POINT ON A STRAIGHT PIN.

5. AVERAGE MASS OF SUBATOMIC PARTICLES Subatomic Particle Electric Charge Mass Number (amu) Location Electron0Electron cloud Proton+11Nucleus Neutron01Nucleus Atomic Mass Unit 1 amu = 1.66 x 10 -24 g

6. ATOMS OF THE SAME ELEMENT WITH DIFFERENT NUMBERS OF NEUTRONS (THEREFORE HAVE DIFFERENT MASSES). Isotopes

7. TWO ISOTOPES OF SODIUM

8. ISOTOPE SYMBOL X : element symbol

9. ISOTOPE SYMBOL A: Mass Number #protons + # neutrons in the nucleus Always larger than Z

10. ISOTOPE SYMBOL Z : Atomic number #protons

11. ISOTOPES OF SODIUM Na 11 Na 11 23 24

12. 2 WAYS TO WRITE ISOTOPE SYMBOL Na 11 23 Or Sodium-23

13. EXAMPLE PROBLEM Write the isotope symbol for the chemical element that has 6 protons and 8 neutrons

14. WORK IT OUT! Take out Whiteboards and Markers Talk over answer with partner Raise board when directed

15. #1 Write the isotope symbol for the chemical element that has 17 protons and 16 neutrons Cl or Chlorine-33 17 33

16. #2 How many protons are in the isotope 54 Cr? (Chromium-54) 24 (like every atom of Chromium)

17. #3 How many neutrons are in the isotope 42 Ca? 22 neutrons

18. #4 How many electrons are in the isotope 23 Na? 11 electrons

19. QUICK BREAK …

20. BY THE END OF THE CLASS TODAY I WILL BE ABLE TO… calculate the average atomic mass of an element using isotopic composition

21. AVERAGE ATOMIC MASS the weighted average of the atomic masses of all naturally occurring isotopes of an element. Where can we find the average atomic mass of each element?

22. WHAT IS THE DIFFERENCE?? The A or ‘Mass Number’ is the mass of that specific isotope The number on the periodic table is the average of all the existing isotopes Example of Carbon

23. LET’S TAKE A LOOK AT PENNIES…

24. The US mint estimates that of all the pennies currently in circulation 66.5% of them are “new” (post-1982) pennies and 33.5% are ‘old’ pennies. A ‘new’ penny weighs 2.5g and an old penny weighs 3.1 g. Use this information to determine the average mass of a penny.

25. HOW DO WE CALCULATE THE AVG. MASS OF A PENNY? Penny YearMass (grams)Percentage in Circulation Post-19822.5g66.5% Pre-19823.1g33.5% 2.5 + 3.1 = 5.6 5.6 ÷ 2 = 2.8 grams

26. WE MUST TAKE INTO CONSIDERATION THE PERCENTAGES OF EACH TYPE OF PENNY! Penny YearMass (grams)Percentage in Circulation Post-19822.5g66.5% Pre-19823.1g33.5% (2.5 x 0.665) + (3.1 x 0.335) = 2.7 grams

27. WHAT IS THE AVERAGE ATOMIC MASS OF COPPER?? IsotopeMass Number Percentage Natural Abundance Copper-636369.17% Copper-656530.83% (63 x 0.6917) + (65 x 0.3083) = 63.61 grams

28. YOU TRY: Rubidium has two common isotopes, Rubidium-85 and Rubidium-87. If the abundance of Rubidium-85 is 72.2% and the abundance of Rubidium-87 is 27.8%, what is the average atomic mass of rubidium?

29. QUIZ TIME