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Isotopes. Atoms with the same number of protons but different numbers of neutrons Ex) Carbon 12 vs. Carbon 14 These atoms have a different mass Chemically alike because still have the same number of protons. Isotopes of Hydrogen. Hydrogen -1 simply called hydrogen
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Isotopes • Atoms with the same number of protons but different numbers of neutrons • Ex) Carbon 12 vs. Carbon 14 • These atoms have a different mass • Chemically alike because still have the same number of protons
Isotopes of Hydrogen • Hydrogen -1 simply called hydrogen • Hydrogen - 2 called deuterium • Hydrogen - 3 called tritium
Development of AMUs • Atomic Mass Units (AMUs) • Protons have a mass of 1 amu • Neutrona have a mass of 1 amu • Electrons have a mass of 0 amu
Atomic Mass • The weighted average mass of the isotopes in a naturally occurring sample of the element • Don’t confuse with “mass number” • To calculate atomic mass you need 3 pieces of information • 1. The number of stable isotopes • 2.The mass of each isotope • 3.The natural percent abundance of each isotope
Atomic Mass • Example Problem - Calculate the atomic mass for element X. One isotope has a mass of 10 amus (10X) and is 20% abundant. The other has a mass number of 11 amus (11X) and an abundance of 80%. • To solve: Multiply the mass number times the abundance than add them together.
Atomic Mass • 10 x 0.20 = 2.0 • 11 x 0.80 = 8.8 • Add 2.0 + 8.8 = 10.8 • The atomic mass of element X is 10.8 amus
Atomic Mass • Your turn. Solve: • What is the atomic mass of Element Z? The isotopes are 16Z, 17Z, 18Z; with percent abundances of 99.759, 0.037, 0.204.
Atomic Mass • Answer • 16 x 0.99759 = 15.961 • 17 x 0.00037 = 0.0063 • 18 x 0.00204 = 0.0367 • 15.961 + 0.0063 + 0.0367 = 16.004 • Tha atomic mass of element Z is 16.004 amus