Chapter 30, Problem 5Q

To determine

Why are the atomic masses of many elements not close to whole members

Answer to Problem 5Q

Solution:

The atomic mass of an element as shown in the periodic table is the average atomic mass of all naturally-occurring isotopes.

Explanation of Solution

The atomic mass of an element as shown in the periodic table is the average atomic mass of all naturally-occurring isotopes.

For example, chlorine occurs as roughly 75% and 25% and so its atomic mass is about 35.4. Atomic mass of an element should be the average atomic mass that a sample of naturally-occurring chlorine would have. Other smaller effects would include the fact that the masses of the nucleons are not exactly 1 atomic mass unit, and that some small fraction of the mass energy of the total set of nucleons is in the form of binding energy. The atomic mass of an element as shown in the periodic table is the average atomic mass of all naturally-occurring isotopes. This is the reason atomic masses of many elements not close to whole members