Chapter 30, Problem 1CQ

To determine

Whether the atom A has a larger atomic number than B.

Answer to Problem 1CQ

No, the atom A need not have larger atomic number than B even the atom A has larger atomic mass.

Explanation of Solution

According to general trend an atom have larger atomic mass correspond to larger atomic number. But there are many exceptions on this generalization. Most of the elements have a number of its isotopes. Sometimes, the heavier isotope of one element may have more mass than a lighter isotope of an atom with a slightly higher atomic number.

For example, consider the atoms ${}^{59}\text{Co}$ and ${}^{58}\text{Ni}$. The atomic mass of ${}^{59}\text{Co}$ is larger than ${}^{58}\text{Ni}$, but the atomic number of cobalt is $27$ and nickel is $28$. That means even the atomic mass is larger, they do not indicate that it have larger atomic number.

Conclusion:

Therefore, the atom A need not have larger atomic number than B even the atom A has larger atomic mass.