Final answer:
The isotope notation for a nucleus with 56 protons and 117 nucleons is written as 117Ba56. It represents a barium isotope with 56 protons and 61 neutrons.
Step-by-step explanation:
The student is asking for the isotope notation for a nucleus with 56 protons and 117 nucleons. In isotope notation, this is represented as the mass number over the atomic number alongside the element symbol. The mass number (A) is the total number of protons and neutrons in the nucleus, which equals the number of nucleons, and the atomic number (Z) is the number of protons. With 56 protons, the element is barium (Ba), because that is the atomic number for barium. As the number of nucleons is 117, the mass number will also be 117. Therefore, the isotope would be written as 117Ba56. To find the number of neutrons, you subtract the number of protons from the number of nucleons: 117 - 56 = 61 neutrons.
To further clarify with an example, the symbol for the isotope of uranium with an atomic number of 92 and a mass number of 235 is 235U92. A similar uranium isotope would have the same bottom number (the atomic number) but a different top number (the mass number) indicating a different number of neutrons. For our barium isotope, the atomic number remains at 56, while the mass number is 117.