Question Video: Understanding Changes in the Neutron Number of an Atomic Nucleus | Nagwa Question Video: Understanding Changes in the Neutron Number of an Atomic Nucleus | Nagwa

Question Video: Understanding Changes in the Neutron Number of an Atomic Nucleus Science

Which of the following does an atomic nucleus become if it loses only neutrons when it undergoes radioactive decay? [A] A different element from the one it was before the decay [B] A different isotope of the element it was before the decay

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Video Transcript

Which of the following does an atomic nucleus become if it loses only neutrons when it undergoes radioactive decay? (A) A different element from the one it was before the decay. (B) A different isotope of the element it was before the decay.

This question asks us whether an atomic nucleus that loses only neutrons changes what element it is a nucleus of or if it changes what isotope of an element it is a nucleus of. If an atomic nucleus only loses neutrons, this means that the number of protons in the nucleus does not change.

To answer this question, we must recall the difference between an element and an isotope of an element. Recall that the number of protons in an atomic nucleus determines what element an atom is an atom of. For example, these two nuclei have the same number of neutrons, three, but different numbers of protons. The nucleus on the left has three protons. If you look at a periodic table, you’ll see that the element with an atomic number of three is lithium. The nucleus on the right has four protons, which makes it a beryllium nucleus. These are nuclei of different elements.

On the other hand, atoms with nuclei that have the same number of protons but different numbers of neutrons are atoms of different isotopes of the same element. In this example, we see two lithium nuclei with different numbers of neutrons. We refer to the nucleus on the right, with four neutrons, as a lithium-7 nucleus. The nucleus on the left is instead a lithium-6 nucleus. It has one fewer neutron than the lithuim-7 nucleus. These nuclei are both lithium nuclei, but with different numbers of neutrons.

Therefore, we say the answer to this question is (B). If an atomic nucleus loses neutrons only, it becomes a different isotope of the element it was before the decay.