Isotopes and Atomic Mass How to write it The isotope of an element can be indicated in two ways: An element is distinguished by always having the same number of protons in the nucleus. Using the elements symbol (numbers can either be to the left or the right of the symbol): However, there can be a variable number of neutrons. 54 Atomic mass 54 An isotope of an element has the Fe Atomic number Fe 26 (may not be present) 26 same atomic number but has a different number of neutrons.
This will affect the average mass Using the elements of an atom of an element. name:
If we take a specific example it will become clear. Next > Iron- 54 Next >
Example Question 1
Iron, atomic number 26, has four Carbon has an atomic number of 6. Its two naturally naturally occurring isotopes. Atomic mass number occurring isotopes are carbon 12 and carbon 13. 54 (number of nucleons) They are: How many neutrons do carbon 12 and 13 have? Fe Atomic number Fe-54, Fe-56, Fe-57, and Fe-58. 26 (number of protons) Carbon -12 Carbon -13 From the table, we can A) 6 7 see the number of protons neutrons nucleons B) 12 13 neutrons in each Fe-54 26 28 54 isotope’s nucleus. Fe-56 26 30 56 C) 7 6 A nucleon, is a Fe-57 26 31 57 D) 13 12 particle that is in the Fe-58 26 32 58 nucleus (either a proton or a neutron). Next > Next >
Question 1 Abundance of each Isotope of Iron
Carbon has an atomic number of 6. Its two naturally If a sample of iron was occurring isotopes are carbon 12 and carbon 13. examined with a mass How many neutrons do carbon 12 and 13 have? spectrometer, the abundance of each Carbon -12 Carbon -13 isotope could be A) 6 7 measured.
B) 12 13 Luckily, tables exist giving Mass spectrometer us this information from Abundance in % C) 7 6 previous experiments. Fe-54 5.8 Fe-56 91.72 D) 13 12 How does this give us Fe-57 2.2 the average mass of Fe-58 0.28 Next > an atom? Next >
1 Question 2 Question 2
Copper has two naturally occurring isotopes (Cu-63 Copper has two naturally occurring isotopes (Cu-63 and Cu-65). and Cu-65). If copper 63 has an abundance of 69.17% what is If copper 63 has an abundance of 69.17% what is the abundance of copper 65? the abundance of copper 65?
Give your answer as a percentage. Give your answer as a percentage. 30.83 (%)
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Calculation of Atomic Mass Number Calculation of Atomic Mass Number
What is the atomic mass of each isotope? Multiply the mass Abundance Atomic mass Atomic mass of each isotope in % abundance Fe-54 53.93612 5.8 3.12829 Atomic mass by the Again, tables give us that Fe-56 55.93439 91.72 51.30302 Fe-54 53.93612 abundance, to data. (This is the atomic Fe-57 56.935396 2.2 1.25258 Fe-56 55.93439 give the mass relative to 1/12 of a Fe-58 57.933278 0.28 0.16221 Fe-57 56.935396 contribution of carbon atom). Total 55.8461 Fe-58 57.933278 each isotope.
Summing the individual abundances, gives the total relative (average) atomic mass of iron.
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Calculation of Atomic Mass Number
If we round up our calculation to 2 d.p. we also get 55.85.