Isotopes

1. Isotopes Isotopes of chlorine 35Cl 37Cl 1717 chlorine - 35 chlorine - 37

2. Hyphen notation • Put the mass number after the name of the element • carbon - 12 • carbon - 14 • uranium - 235

3. Isotopes • Chlorine-37 • atomic #: • mass #: • # of protons: • # of electrons: • # of neutrons: 17 37 17 17 20

4. 9 10 9 9 19 • Find the • number of protons • number of neutrons • number of electrons • Atomic number • Mass Number 19 F 9

5. 35 45 35 35 80 • Find the • number of protons • number of neutrons • number of electrons • Atomic number • Mass Number 80 Br 35

6. if an element has an atomic number of 34 and a mass number of 78 what is the • number of protons • number of electrons • number of neutrons • complete nuclear symbol 34 34 44 78 Se 34

7. if an element has 91 protons and 140 neutrons what is the • Atomic number • Mass number • Number of electrons • Complete symbol 91 231 91 231 Pa 91

8. if an element has 78 electrons and 117 neutrons what is the • Atomic number • Mass number • number of protons • Complete symbol 78 195 78 195 Pt 78

9. An atom of zinc has a mass number of 65. A. Number of protons in the zinc atom 30 B. Number of neutrons in the zinc atom 35 What is the mass number of a zinc isotope with 37 neutrons? 67

10. 16 O 8 Write the nuclear symbols for atoms with the following: A. 8 p+, 8 n, 8 e- B. 17p+, 20n, 17e- C. 47p+, 60 n, 47 e- 37 Cl 17 107 Ag 47

11. An atom has 14 protons and 20 neutrons. A. It has atomic number 14 B. It has a mass number of 34 C. The element is Si D. Another isotope of this element would be 36X 14

12. Calculating averages • You have five rocks, four with a mass of 50 g, and one with a mass of 60 g. What is the average mass of the rocks? • Total mass = 4 x 50g + 1 x 60g = 260g • Average mass = 4 x 50g + 1 x 60g = 260g 5 5

13. Avg. Atomic Mass Average Atomic Mass • weighted average of all isotopes • decimal numbers on the Periodic Table • round to 2 decimal places

14. Average Atomic Mass • Is not a whole number because it is an average.

15. Avg. Atomic Mass Average Atomic Mass • EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O. 16.00 amu

16. Avg. Atomic Mass Average Atomic Mass • EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37. 35.40 amu

17. Average Atomic Mass • Magnesium has three isotopes: 78.99% magnesium - 24 with a mass of 23.9850 amu, 10.00% magnesium - 25 with a mass of 24.9858 amu, and the rest is magnesium - 26 with a mass of 25.9826 amu. What is the average atomic mass of magnesium? • If not told otherwise, the mass of the isotope is the mass number in amu 24.30 amu

18. Atomic Mass • Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass of 64.93 amu. 63.55 amu

19. Learning Check Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the atomic mass of gallium?

20. Solution Ga-69 68.9 amu x 60.2 = 41.5 amu for 69Ga 100 Ga-71 70.9 amu x 39.8 = 28.2 amu for 71Ga 100 Atomic mass Ga = 69.7 amu

21. Finding An Isotopic Mass A sample of boron consists of 10B (mass 10.0 amu) and 11B (mass 11.0 amu). If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope?

22. Assign X and Y values: X = % 10B Y = % 11B Determine Y in terms of X X + Y = 100 Y = 100 - X Solve for X: X (10.0) + (100 - X )(11.0) = 10.8 100 100 Multiply through by 100 10.0 X + 1100 - 11.0X = 1080

23. Collect X terms 10.0 X - 11.0 X = 1080 - 1100 - 1.0 X = -20 X = -20 = 20 % 10B - 1.0 Y = 100 - X % 11B = 100 - 20% = 80% 11B

24. Learning Check Copper has two isotopes 63Cu (62.9 amu) and 65Cu (64.9 amu). If the average atomic mass of Cu is 63.55 amu, what is the % abundance of each copper isotope?

25. Solution 62.9X + 6490 - 64.9X = 6355 -2.0 X = -135 X = 67.5 %