Question

Choose the correct answer. The difference between the mass number of an isotope and its atomic number is (a) directly related to the identity of the element; (b) the number of electrons; (c) the number of neutrons; (d) the number of isotopes.

Short answer

(c) the number of neutrons

Step-by-step solution

Understand Mass Number

The mass number of an isotope is defined as the total number of protons and neutrons in its nucleus.

Understand Atomic Number

The atomic number of an element is the number of protons in the nucleus of an atom. This is a unique identifier for each element.

Calculate the Difference

The difference between the mass number and the atomic number of an isotope is given by subtracting the atomic number (number of protons) from the mass number (total number of protons and neutrons).

Find the Relationship

The difference represents the number of neutrons in the isotope, since: \[ \text{Number of neutrons} = \text{Mass number} - \text{Atomic number} \]

Choose Correct Answer

Based on the calculated relationship, the correct answer is (c) the number of neutrons.

Key concepts

mass number

The mass number is a fundamental concept in understanding the structure of an atom. It tells us the total number of protons and neutrons in an atom's nucleus. Remember that protons and neutrons are collectively called nucleons.
For example, if an atom has 6 protons and 7 neutrons, its mass number is 13. This mass number helps distinguish between different isotopes of the same element.

Isotopes are atoms with the same number of protons but different numbers of neutrons.

atomic number

The atomic number is like an atom's unique fingerprint. It specifies the number of protons in the nucleus, which determines the element's identity. For instance, all carbon atoms have 6 protons, so the atomic number of carbon is 6. This atomic number is crucial because it defines the chemical behavior of an element. Since all atoms of a given element have the same number of protons, the atomic number does not change among isotopes.

neutrons in isotopes

The number of neutrons in an atom can vary, leading to different isotopes of the same element. To find the number of neutrons in an isotope, you subtract the atomic number from the mass number:
\(\text{Number of neutrons} = \text{Mass number} - \text{Atomic number}\)

For example, if an isotope has a mass number of 14 and an atomic number of 6, then it has 8 neutrons:
\[14 - 6 = 8\]\

These neutrons play a vital role in the stability of the atom and its isotopes' behavior in nuclear reactions.