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ISOTOPES

ISOTOPES. Atom Review. All matter is made up of elements (e.g. carbon, hydrogen, etc.). The smallest part of an element is called an atom. Atoms of different elements contain different numbers of protons. The mass of an atom is almost entirely due to the number of protons and neutrons.

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ISOTOPES

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  1. ISOTOPES

  2. Atom Review All matter is made up of elements (e.g. carbon, hydrogen, etc.). The smallest part of an element is called an atom. Atoms of different elements contain different numbers of protons. The mass of an atom is almost entirely due to the number of protons and neutrons.

  3. The Atom The atom consists of two parts: 1. The nucleus which contains: protons neutrons 2. Orbiting electrons.

  4. Mass number = number of protons + number of neutrons A X Element symbol Z Atomic number = number of protons Isotopic Notation

  5. A X Z A = number of protons + number of neutrons (mass number) Z = number of protons (atomic number) A – Z = number of neutrons Number of neutrons = Mass Number – Atomic Number

  6. ISOTOPES • THE NUMBER OF PROTONS FOR A GIVEN TYPE OF ATOM NEVER CHANGES. • THE NUMBER OF NEUTRONS CAN CHANGE. • TWO ATOMS WITH THE SAME NUMBER OF PROTONS BUT DIFFERENT NUMBERS OF NEUTRONS ARE CALLED ISOTOPES.

  7. ISOTOPES ISOTOPES ARE ATOMS WITH THE SAME NUMBER OF PROTONS BUT DIFFERENT NUMBER OF NEUTRONS.

  8. 238 235 U U 92 92 EXAMPLES OF URANIUM ISOTOPES:

  9. 238 235 U U 92 92 EXAMPLES OF URANIUM ISOTOPES: Isotopes of any particular element contain the same number of protons, but different numbers of neutrons.

  10. Atomic Weight To calculate the atomic weight (average atomic mass) for a particular element we must consider how much of one isotope of an element exists versus another isotope of the same element. These are the "natural" abundances (% abundance) on earth.

  11. Rule for Calculating Atomic Weight To calculate the average atomic weight, each exact atomic weight is multiplied by its percent abundance (expressed as a decimal). Then, add the results together and round off to an appropriate number of significant figures.

  12. mass number exact weight percent abundance 14 14.003074 99.63 15 15.000108 0.37 Example #1: Nitrogen This is the solution for nitrogen: (14.003074) (0.9963) + (15.000108) (0.0037) = 14.007

  13. mass number exact weight percent abundance 24 23.985042 78.99 25 24.985837 10.00 26 25.982593 11.01 Practice Problem # 1 Calculate the average atomic weight for magnesium:

  14. Answer # 1 This is the solution for magnesium: (23.985042) (0.7899 ) + (24.985837) (0.1000) + (25.982593) (0.1101)= 24.305

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