2. If you change the number of… It will affect the…And the result will be a… Protons Electrons Neutrons Identity of the atom completely different atom ChargeIon MassIsotope

3. They are atoms of the same element that have different numbers of neutrons. It’s just a change in the number of neutrons!!! Why are you making this complicated?

4. Hydrogen has 3 isotopes There are 3 different “versions” of a hydrogen atom Note how the number of protons never change!!!

5. Hydrogen has 3 isotopes There are 3 different “versions” of a hydrogen atom Having more neutrons increases the mass

6. Hydrogen has 3 isotopes There are 3 different “versions” of a hydrogen atom Mass number = 1 Mass number = 2 Mass number = 3

7. 6 C 12.01115 10 Ne 20.180 13 Al 26.982

8. 1 H 1.00797 This atomic mass is the one number that best represents the mass of all three versions of hydrogen.

9. 1 H 1.00797 No atom of hydrogen anywhere in the universe actually has this mass.

10. 1 H 1.00797 This number is a “weighted” average of the masses of every isotope of hydrogen

11. 1. First, you have to know the mass of each isotope 2. Second, you have to know the percent abundance * of each isotope *see next slide

12. Percent abundance is how often that particular isotope occurs in a sample of the element Sample of Magnesium A sample of magnesium collected anywhere in the universe will contain three isotopes of magnesium.

13. These are the percent abundances of each isotope of magnesium Sample of Magnesium 78.90% of this magnesium will be the isotope named “magnesium 24” 10.00% of this magnesium will be the isotope named “magnesium 25” 11.10% of this magnesium will be the isotope named “magnesium 26”

14. This data will be provided to you in problems or you will be given a table where you can look it up. Sample of Magnesium 78.90% of this magnesium will be the isotope named “magnesium 24” 10.00% of this magnesium will be the isotope named “magnesium 25” 11.10% of this magnesium will be the isotope named “magnesium 26”

15. The formula (Mass of isotope #1)(percent abundance) 100 (Mass of isotope #2)(percent abundance) 100 (Mass of isotope #3)(percent abundance) 100

16. # protons# neutronsMass (amu’s) % abundance Isotope 1 (magnesium-24) 12 23.985045 78.90% Isotope 2 (magnesium-25) 1213 24.985839 10.00% Isotope 3 (magnesium-26) 1214 25.982595 11.10%

17. Using the formula for calculating a weighted average 23.985045(.7890) +24.985839(.1000) + 25.982595(.1110) 24.306852 amu’s Since its a “weighted” average this number has more influence since this mass occurs 79% of the time It’s NOT just a straight average where you add the masses and divide by 3 Note how the % abundances were converted to decimals (just divide each by 100)

19. IsotopeMass% abundance #1 49.9460464.35 #2 51.94051083.79 #3 52.9406519.50 #4 53.9388822.36

20. 49.946046(0.0435) 51.940510(0.8379) +52.940651 ( 0.0950) 53.938882 ( 0.0236) 51.995926 amu’s

21. Terms associated with isotopes

22. Atomic number = the number of protons  It’s the same as the element’s position on the periodic table  For example, carbon is the 6 th element on the table, so its atomic number is 6 which means it has 6 protons (and 6 electrons if it’s a neutral atom)

23. Atomic mass = the “weighted” average mass of all the different isotopes of an atom  This is the “weird” number on the periodic table that usually has a bunch of places past the decimal point

24. Mass number = the sum of protons + neutrons  This one kind of makes sense because the electrons essentially don’t have any mass  This HAS to be a whole number because you can’t have part of a proton or neutron  Mass number is NOT given on the periodic table

25. 1. What is the mass number of a carbon atom that has 6 neutrons? 7 neutrons? 2. How many neutrons does a nitrogen atom have if its mass number is 14? 3. How many neutrons does a chlorine atom have if its mass number is 36? 4. What is the atomic number of neon? 5. What is the atomic mass of neon?

26. 1. 12 and 13 2. 7 3. 19 4. 10 5. 20.180 amu’s

27. A shorthand way to write isotopes

28. AXZAXZ “A” is the symbol for Mass Number (#protons + #neutrons) “Z” is the symbol for Atomic Number (# of protons) “X” will be the symbol of the element

29. Yo! If you’re doin’ chem problems I feel bad for you son…. I got 99 problems, and here’s the first one….HIT ME!!!!

36. How many protons, electrons, and neutrons are in this isotope? 41 Ca 2+ 20

37. How many protons, electrons, and neutrons are in this isotope? 41 Ca 2+ 20 20 protons, 18 electrons, 21 neutrons

38. How many protons, electrons, and neutrons? 1. 56 Fe 2+ 26 2. 27 Al 3+ 13 3. 79 Se 2- 34

39. How many protons, electrons, and neutrons? 1. 56 Fe 2+ 26 26, 24, 30 2. 27 Al 3+ 13 13, 10, 14 3. 79 Se 2- 34 34, 36, 45

42.  35 Cl 17 is the same as 35 17 Cl  Might also see “Cl-35” or “chlorine-35”