Why is it impossible for an element to have an atomic number of 110.5?

• A. Atomic numbers can be fractional if the element is radioactive.
• B. Elements with atomic numbers above 100 are unstable and cannot exist.
• C. Atomic numbers represent the average mass of an atom, which can be fractional.
• D. Atomic numbers must be whole numbers because they represent the number of protons in an atom.

Answer: (D)

Verified step by step guidance

1. Understand that the atomic number of an element is defined as the number of protons in the nucleus of an atom.
2. Recognize that protons are discrete particles and cannot be divided, so the number of protons must be a whole number (an integer).
3. Note that atomic numbers cannot be fractional because you cannot have half a proton; each proton contributes exactly one unit to the atomic number.
4. Clarify that atomic numbers are not averages or related to mass; instead, they uniquely identify each element based on its proton count.
5. Conclude that an atomic number like 110.5 is impossible because it violates the fundamental definition of atomic number as a count of whole protons.