Unit 3: The Atom Relative Atomic Mass (Isotopes) Intro: ● Define Isotope: Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number 1. 2. ● Compare and contrast the physical and chemical properties in an isotope: ● Give the formula for calculating the average atomic mass: Here are three isotopes of an element: 12 13 6C 6C 14 6C a. The element is: carbon b. The number 6 refers to the _a #, # of p c. The numbers 12, 13, and 14 refer to the M# of, p+n d. How many protons and neutrons are in the first isotope? _________________ e. How many protons and neutrons are in the second isotope? _________________ f. How many protons and neutrons are in the third isotope? _________________ Complete the following chart: Isotope name Atomic # mass # Potassium-37 (K) 19 37- Oxygen-17 (O) 8 Uranium-235 (U) 92 Uranium-238 (U) 92 # of protons # of neutrons # of electrons 19 = 18 19 17- 8= 9 8 235- 92 = 143 92 238- 92 = 143 92 Boron-10 (B) 5 10- 5= 5 5 Boron-11 (B) 5 11- 5= 6 5 DIRECTIONS: For the following problems, show your work! Be thorough. 3. Naturally occurring europium (Eu) consists of two isotopes was a mass of 151 and 153. Europium-151 has an abundance of 48.03% and Europium-153 has an abundance of 51.97%. What is the atomic mass of europium? 4. Strontium consists of four isotopes with masses of 84 (abundance 0.50%), 86 (abundance of 9.9%), 87 (abundance of 7.0%), and 88 (abundance of 82.6%). Calculate the atomic mass of strontium. (84 x.5) + (86 x 99) + ( 88 x 826)= 87.712 5. Titanium has five common isotopes: 46Ti (8.0%), 47Ti (7.8%), 48Ti (73.4%), 49Ti (5.5%), 50 6. Ti (5.3%). What is the average atomic mass of titanium? Calculate the atomic mass of copper if copper-63 has a mass of 62.978 amu and is 69.17% abundant and copper-65 has a mass of 64.894 and is 30.83% abundant. 7. Boron exists in two isotopes, boron-10 and boron-11. Based on the atomic mass, which isotope should be more abundant? 10.81 8. Lithium-6 is 4% abundant and lithium-7 is 96% abundant. What is the average mass of lithium? 9. Iodine is 80% 127I, 17% 126I, and 3% 128I. Calculate the average atomic mass of iodine. 10. The natural abundance for boron isotopes is 19.9% 10B and 80.1% 11B . Calculate boron’s atomic Mass. 11. Hydrogen is 99% 1H, 0.8% 2H, and 0.2% 3H. Calculate its average atomic mass. 12. Rubidium is a soft, silvery-white metal that has two common isotopes, 85Rb and 87Rb. If the abundance of 85Rb is 80.2% and the abundance of 87Rb is 19.8%, what is the average atomic mass of rubidium? 13. What is the atomic mass of hafnium if, out of every 100 atoms, 5 have a mass of 176, 19 have a mass of 177, 27 have a mass of 178, 14 have a mass of 179, and 35 have a mass of 180.0? 14. Why is the mass of a carbon-12 atom reported as 12.011?
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