Problem

Iodine has a lower atomic mass than tellurium (126.90 for iodine, 127.60 for tellurium) even though it has a higher atomic number (53 for iodine, 52 for tellurium). Explain.

Relevant Solution
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Hi everyone. This problem reads the atomic mass of cobalt 58.933 atomic mass units is slightly higher than that of nickel 58.693 atomic mass units. Despite cobalt having a lower atomic number identify the statement that explains why. Okay, so this is what we want to do statement a reads. Cobalt has more neutrons than nickel. Be The isotopes of nickel are more stable than that of cobalt. Sea. Cobalt has one isotope while nitrogen has multiple isotopes which affects its atomic mass greatly. So let's go ahead and talk about isotopes for both. Okay, so we have cobalt and we have nickel. Okay, so cobalt only has one natural isotope and that isotope is cobalt 59 Which is 58.9 atomic mass units. Okay, nickel has multiple natural isotopes. It actually has five. Okay. And we're gonna list those out here. So we have Nickel 58 and it has an abundance of 68.077%. With an atomic mass unit of 57.935. Okay, then we have Nickel which has an abundance of 26.2-3%. And an atomic mass unit of 59.931. Then we have Nickel 61 which has an abundance of 1.140% abundance and an atomic mass unit of 60.931 atomic mass units followed by Nickel 62 which has an abundance of 3.635 And an atomic mass unit of 61. Atomic mass units. And lastly Nickel Which has an abundance of 0. With an atomic mass unit of 63.928. Okay. So looking at this With our isotopes for Nickel, the isotope with the greatest abundance is Nickel 58 with 57.935 Atomic mass units. So this means it has more weight to the average atomic mass. And this is going to be the reason why the atomic mass of cobalt is slightly higher than that of nickel, despite cobalt having a lower atomic number. Okay, the statement that explains why is statement. See that cobalt has one isotope while Nicole has multiple isotopes, which affects its atomic mass greatly. Okay, so our correct answer for this problem is going to be answer choice C. Okay, so that is it for this problem. I hope this was helpful.