Isotopes

1
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

2
Isotopes of Hydrogen

• Hydrogen -1 simply called hydrogen
• Hydrogen - 2 called deuterium
• Hydrogen - 3 called tritium

3
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

4
Atomic Mass

• The weighted average mass of the isotopes in a
  naturally occurring sample of the element
• Dont 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

5
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.

6
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

7
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.

8
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