Mass Weight Rounding Problem

[rooksai]

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I understand the concepts fine when it comes to determining the number of protons, neutrons, and electrons. However I just don't get the rounding part because it is weird.

Problem:

Determine the number of protons, neutrons, and electrons in a nickel 58 atom.

In the periodic table, it shows that Nickel has a mass of 58.7, however, the book solution rounds down Nickel's mass to 58, and uses that to determine the number of neutrons.

Book Explanation: Nickel has an atomic number of 28 and a mass number of 58. Nickel will have then 28 protons, 28 electrons or 30 neutrons.

If I would have done it: I will have rounded it up to 59, since periodic table shows Nickel at 58.7. Do I just round down for every element, even for an element such as Copper which has a mass of 58.9?

Monkeyvokes pointed out the obvious @@ This post is done.

 

[monkeyvokes]

I understand the concepts fine when it comes to determining the number of protons, neutrons, and electrons. However I just don't get the rounding part because it is weird.

Problem:

Determine the number of protons, neutrons, and electrons in a nickel 58 atom.

In the periodic table, it shows that Nickel has a mass of 58.7, however, the book solution rounds down Nickel's mass to 58, and uses that to determine the number of neutrons.

Book Explanation: Nickel has an atomic number of 28 and a mass number of 58. Nickel will have then 28 protons, 28 electrons or 30 neutrons.

If I would have done it: I will have rounded it up to 59, since periodic table shows Nickel at 58.7. Do I just round down for every element, even for an element such as Copper which has a mass of 58.9?

Well.. the numbers on the periodic table are a weighted mean of the isotopes found in nature (weighted by their prevalence). Sounds like your question was specifically referring to the isotope Ni 58?