What are isotopes?

What are isotopes?

• A. Atoms of different elements with similar properties
• B. Atoms with different numbers of protons
• C. Atoms that have the same mass
• D. Atoms of the same element that have different numbers of neutrons

Answer: (D)

Isotopes are variants of the same element that differ in the number of neutrons. Because they share the same number of protons, they are the same element and have the same chemical properties, but the different neutron counts give them different masses. For example, carbon‑12 and carbon‑14 are both carbon because they each have 6 protons, but carbon‑12 has 6 neutrons while carbon‑14 has 8 neutrons, so their masses differ (and carbon‑14 can be radioactive). The other descriptions don’t fit isotopes: atoms of different elements with similar properties are not isotopes since isotopes must be the same element; atoms with different numbers of protons would be different elements altogether; and having the same mass would not reflect the variation in neutron numbers that defines isotopes.

Isotopes are variants of the same element that differ in the number of neutrons. Because they share the same number of protons, they are the same element and have the same chemical properties, but the different neutron counts give them different masses. For example, carbon‑12 and carbon‑14 are both carbon because they each have 6 protons, but carbon‑12 has 6 neutrons while carbon‑14 has 8 neutrons, so their masses differ (and carbon‑14 can be radioactive).

The other descriptions don’t fit isotopes: atoms of different elements with similar properties are not isotopes since isotopes must be the same element; atoms with different numbers of protons would be different elements altogether; and having the same mass would not reflect the variation in neutron numbers that defines isotopes.