Report

Calculating Average Atomic Mass Introduction • The value for atomic mass for a particular element is the average atomic mass. • Each sample of an element is composed of a mixture of different isotopes. • Therefore, we need to average the masses of the isotopes to find the average atomic mass. Calculations • Copper has two common isotopes. o o 63Cu is 69.15% of copper samples. 65Cu is 30.85% of copper samples. • We would expect the average atomic mass to be somewhere in between 63 and 65. Calculations • Copper has two common isotopes. o o 63Cu is 69.15% of copper samples. 65Cu is 30.85% of copper samples. • To find the average atomic mass o multiply the mass number by the percentages (as a decimal value) Calculations • Copper has two common isotopes. o o 63Cu is 69.15% of copper samples. 65Cu is 30.85% of copper samples. • To find the average atomic mass o multiply the mass number by the percentages (as a decimal value) • 63 × 0.6915 = 43.56 • 65 × 0.3085 = 20.05 Calculations • Copper has two common isotopes. o o 63Cu is 69.15% of copper samples. 65Cu is 30.85% of copper samples. • To find the average atomic mass o multiply the mass number by the percentages (as a decimal value) • 63 × 0.6915 = 43.56 • 65 × 0.3085 = 20.05 Calculations • Copper has two common isotopes. o o 63Cu is 69.15% of copper samples. 65Cu is 30.85% of copper samples. • To find the average atomic mass o multiply the mass number by the percentages (as a decimal value) • 63 × 0.6915 = 43.56 • 65 × 0.3085 = 20.05 Calculations • Copper has two common isotopes. o o 63Cu is 69.15% of copper samples. 65Cu is 30.85% of copper samples. • To find the average atomic mass o multiply the mass number by the percentages (as a decimal value) • 63 × 0.6915 = 43.56 • 65 × 0.3085 = 20.05 o and add the values Calculations • Copper has two common isotopes. o o 63Cu is 69.15% of copper samples. 65Cu is 30.85% of copper samples. • To find the average atomic mass o multiply the mass number by the percentages(as a decimal value) • 63 × 0.6915 = 43.56 • 65 × 0.3085 = 20.05 o and add the values • 43.56 + 20.05 = Calculations • Copper has two common isotopes. o o 63Cu is 69.15% of copper samples. 65Cu is 30.85% of copper samples. • To find the average atomic mass o multiply the mass number by the percentages(as a decimal value) • 63 × 0.6915 = 43.56 • 65 × 0.3085 = 20.05 o and add the values • 43.56 + 20.05 = Calculations • Copper has two common isotopes. o o 63Cu is 69.15% of copper samples. 65Cu is 30.85% of copper samples. • To find the average atomic mass o multiply the mass number by the percentages(as a decimal value) • 63 × 0.6915 = 43.56 • 65 × 0.3085 = 20.05 o and add the values • 43.56 + 20.05 = 63.61 Calculations • Iron has three common isotopes. o o o 54Fe is 5.85% of iron samples. 56Fe is 91.75% of iron samples. 58Fe is 2.82% of iron samples. • We would expect the average atomic mass to be somewhere in between 54 and 58. Calculations • Iron has three common isotopes. o o o 54Fe is 5.85% of iron samples. 56Fe is 91.75% of iron samples. 58Fe is 2.82% of iron samples. • multiply the mass number by the percentages o 54 × 0.0585 = 3.16 o 56 × 0.9175 = 51.38 o 58 × 0.0282 = 1.61 Calculations • Iron has three common isotopes. o o o 54Fe is 5.85% of iron samples. 56Fe is 91.75% of iron samples. 58Fe is 2.82% of iron samples. • multiply the mass number by the percentages o 54 × 0.0585 = 3.16 o 56 × 0.9175 = 51.38 o 58 × 0.0282 = 1.61 • and add the values Calculations • Iron has three common isotopes. o o o 54Fe is 5.85% of iron samples. 56Fe is 91.75% of iron samples. 58Fe is 2.82% of iron samples. • multiply the mass number by the percentages o 54 × 0.0585 = 3.16 o 56 × 0.9175 = 51.38 o 58 × 0.0282 = 1.61 • and add the values o 3.16 + 51.38 + 1.61 = 56.15 Try one on your own • Magnesium has three common isotopes. o o o 24Mg is 78.99% of magnesium samples. 25Mg is 10.00% of magnesium samples. 26Mg is 11.01% of magnesium samples. • What would be the average atomic mass of Mg? Do not move on until you try this problem. Try one on your own • Magnesium has three common isotopes. o o o 24Mg is 78.99% of magnesium samples. 25Mg is 10.00% of magnesium samples. 26Mg is 11.01% of magnesium samples. • What would be the average atomic mass of Mg? o 24 × 0.7899 = 18.96 o 25 × 0.1000 = 2.50 o 26 × 0.1101= 2.86 Try one on your own • Magnesium has three common isotopes. o o o 24Mg is 78.99% of magnesium samples. 25Mg is 10.00% of magnesium samples. 26Mg is 11.01% of magnesium samples. • What would be the average atomic mass of Mg? o 24 × 0.7899 = 18.96 o 25 × 0.1000 = 2.50 o 26 × 0.1101= 2.86 o 18.96 + 2.50 + 2.86 = 24.32 Try one on your own • Chlorine has two common isotopes. o o 35Cl is 75.76% of chlorine samples. 37Clg is 24.24% of chlorine samples. • What would be the average atomic mass of Cl? Do not move on until you try this problem. Try one on your own • Chlorine has two common isotopes. o o 35Cl is 75.76% of chlorine samples. 37Clg is 24.24% of chlorine samples. • What would be the average atomic mass of Cl? o 35 × 0.7576 = 26.52 o 37 × 0.2424 = 8.97 Try one on your own • Chlorine has two common isotopes. o o 35Cl is 75.76% of chlorine samples. 37Clg is 24.24% of chlorine samples. • What would be the average atomic mass of Cl? o 35 × 0.7576 = 26.52 o 37 × 0.2424 = 8.97 o 26.52 + 8.97 = 35.48 Summary • To find the average atomic mass of an element, we need to know the percent abundance of each isotope. • We multiply the mass number of each isotope by the percentages (as a decimal number) and add the values for each isotope to get the average atomic mass.