Calculating Average Mass

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Presentation transcript:

Calculating Average Mass Atomic mass is the average of all the naturally isotopes of that element. Copper = 63.546 amu Isotope Symbol Composition of the nucleus Mass in (amu) Relative Abundance (% in nature) Copper-63 63 29 29 protons 34 neutrons 62.93 69.2 % Copper-65 65 36 neutrons 64.93 30.8 % Cu Cu x Mass (amu) Relative abundance (% as a decimal) Copper-63 62.93 amu x 0.692 = 43.54756 amu + Copper-65 64.93 amu x 0.308 = 19.99844 amu 63.546 amu Periodic Table of Elements

Your Turn (Calculate Average Mass) Isotope Symbol Atomic # neutrons electrons Mass Number (p+ + n0) Isotope Mass in (amu) Relative abundance Carbon-12 6C 6 12 - 6 = 6 6 - 6 + 6 = 12 12.000 98.89% Carbon-13 13 – 6 = 7 6 + 7 = 13 13.003 1.11% 12 13 x Mass (amu) Relative abundance (% as a decimal) Carbon-12 12.000 amu x 0.9889 = 11.8668 amu + Carbon-13 13.003 amu x 0.0111 = 0.1443333 amu 12.0111333 amu 12.01 amu Atomic # C Carbon 6 12.011 Atomic mass (average)

Your Turn (Calculate Average Mass) Isotope Symbol Atomic # neutrons electrons Mass Number (p+ + n0) Isotope Mass in (amu) Relative abundance Nitrogen-14 N 14.003 99.63% Nitrogen-15 15.000 0.37% Chlorine-35 Cl 34.969 75.77% Chlorine-37 36.966 24.23% 14 7 7- 14 14-7=7 7 15 7 7- 15 15-7=8 7 35 17 17- 35 35-17=18 17 37 17 17- 37 37-17=20 17 x Mass (amu) Relative abundance (% as a decimal) Nitrogen-14 14.003 amu x 0.9963 = 13.9511889 amu + Nitrogen-15 15.000 amu x 0.0037 = 0.0555 amu 14.0066889 amu N Nitrogen 7 14.007 14.007 amu

Your Turn (Calculate Average Mass) Isotope Symbol Atomic # neutrons electrons Mass Number (p+ + n0) Isotope Mass in (amu) Relative abundance Nitrogen-14 N 14.003 99.63% Nitrogen-15 15.000 0.37% Chlorine-35 Cl 34.969 75.77% Chlorine-37 36.966 24.23% 14 7 7- 14 14-7=7 7 15 7 7- 15 15-7=8 7 35 17 17- 35 35-17=18 17 37 17 17- 37 37-17=20 17 x Mass (amu) Relative abundance (% as a decimal) Chlorine-35 34.969 amu x 0.7577 = 26.4960113 amu + Chlorine-37 36.966 amu x 0.2423 = 8.9568618 amu 35.4528731 amu Cl Chlorine 17 35.453 35.453 amu

Pb Calculate Average Mass Mass # = p+ + n0 1.37 100 + 204 206 207 208 Lead 82 207.20 Calculate Average Mass Mass # = p+ + n0 82p 122n 82p 124n 82p 125n 82p 126n % abundance: 1.37% 26.26% 20.82% 51.55% Mass # 204 206 207 208 1.37 100 No amu mass shown. Use mass # instead. x Mass (amu) Relative abundance (% as a decimal) Lead-204 204 x 0.0137 = 2.7948 Lead-206 206 x 0.2626 = 54.0956 Lead-207 207 x 0.2082 = 43.0974 + Lead-208 208 x 0.5155 = 107.224 207.2118 207.21

Your Turn (Calculate Average Mass) Isotope Symbol Atomic # neutrons electrons Mass Number (p+ + n0) Isotope Mass in (amu) Relative abundance Helium-3 2He 2 1 2 - 3 3.0160 0.0001% Helium-4 4 4.0026 99.9999% 3 4 x Mass (amu) Relative abundance (% as a decimal) Helium-3 3.0160 amu x 0.000001 = 0.000003016 amu + Helium-4 4.0026 amu x 0.999999 = 4.002595997 amu 4.002599013 amu 4.0026 amu Atomic # He Helium 2 4.0026 Atomic mass (average)