Video: Identifying the Set of Numbers of Protons, Neutrons, and Electrons That Would Form an Ion with a Given Mass Number and Charge in a List of Sets

Which of the following sets could combine to form an ion with a mass number of 83 and a net charge of −1? [A] 41 neutrons, 42 protons, and 41 electrons [B] 42 neutrons, 41 protons, and 40 electrons [C] 42 neutrons, 41 protons, and 41 electrons [D] 45 neutrons, 38 protons, and 37 electrons [E] 45 neutrons, 38 protons, and 39 electrons

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Video Transcript

Which of the following sets could combine to form an ion with a mass number of 83 and a net charge of minus one? (A) 41 neutrons, 42 protons, and 41 electrons. (B) 42 neutrons, 41 protons, and 40 electrons. (C) 42 neutrons, 41 protons, and 41 electrons. (D) 45 neutrons, 38 protons, and 37 electrons. Or (E) 45 neutrons, 38 protons, and 39 electrons.

An atom is the smallest particle of an element that can exist. Atoms are composed of a central nucleus surrounded by various electron-containing shells. The nucleus is positively charged because it contains positively charged protons. The nucleus also contains neutral particles. These particles have no charge and are called neutrons. The shells around the nucleus contain negatively charged particles called electrons. Protons, neutrons, and electrons are known as subatomic particles.

Atoms are electrically neutral, which means that they contain an equal number of protons and electrons, in other words, an equal number of positive and negative charges. An ion is an atom or molecule which has lost or gained one or more electrons and thus has a net charge. In other words, ions are electrically charged particles, and the number of protons is not equal to the number of electrons.

The question asks about an ion with a net charge of minus one. When an ion has a negative one charge, this means that there is one more electron than there are protons. In other words, the atom has gained an electron to form a minus one charge. The question also asks for an ion with a mass number of 83. Mass number is the sum of the number of protons plus the number of neutrons in an atom or ion.

We can express the number of protons, neutrons, and electrons for this ion using atomic notation, where 𝑥 is the symbol of the element. And we do not yet know which element this is. 𝐴 is the mass number, in other words, the number of protons plus neutrons. And zed or zee, the atomic number, in other words, the number of protons.

We know 𝐴, the mass number, is 83. We do not know the number of protons, 𝑍. But we know the charge is negative one, in other words, 𝑥 one minus. We have not been given enough information to determine the number of protons, neutrons, and electrons in the ion in this question. And so, our only option is to look at the possible answers to see which answer gives a mass number of 83 and a net charge of minus one, in other words, one excess electron.

Calculating the mass number for each answer by adding the number of protons and neutrons, we see that the mass number for each is 83. So, the last step is to compare the number of protons and electrons in each answer and see which answer has one excess electron.

In answer (A), there is one more proton than there are electrons. In answer (B), there is one more proton than there are electrons. In answer (C), the number of protons equals the number of electrons, so this cannot be an ion. In answer (D), there is one more proton than electrons. It is only in answer (E) that there is one more electron than there are protons, in other words, giving an ion with a minus one charge.

Finally, the set which could combine to form an ion with a mass number of 83 and a net charge of minus one is 45 neutrons, 38 protons, and 39 electrons.

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