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Question Video: Explaining Why Atoms Do Not Have a Charge Chemistry • 7th Grade

Why do atoms not have an overall charge?

05:48

Video Transcript

Why do atoms not have an overall charge? (A) The number of electrons equals the number of neutrons. (B) The number of electrons equals the number of protons. (C) The number of neutrons equals the number of protons. (D) The number of electrons and neutrons equals the number of protons. (E) The number of electrons plus protons equals the number of neutrons.

This question asks about overall charge. Charge can be positive or negative like the opposite ends of a magnet. If there’s no charge, we can say that the charge is neutral. Overall charge refers to the charge of the atom as a whole. And if we want to know about the atom’s overall charge, we need to know about the charges of the subatomic particles that make up the atom.

Protons, found in the nucleus, have a positive charge. Neutrons, also found in the nucleus, have no charge or a neutral charge. And electrons, found in the electron cloud outside the nucleus, have a negative charge. So in other words, this question’s asking, how do the numbers of protons, neutrons, and electrons result in an atom not having an overall positive or negative charge? It’s important to know that the charge of a positive proton and the charge of a negative electron have equal strength. In other words, putting together one proton with a positive charge and one electron with a negative charge will balance out to be neutral.

In fact, the only way to have a neutral atom is for the total positive charge to be equal in strength to the total negative charge. This arrangement is described in answer (B), the number of electrons equals the number of protons. If the number of electrons equals the number of protons, then the positive and negative charges of the protons and electrons will balance out and become neutral. When an atom gains or loses electrons to become an ion, it no longer has an equal number of electrons and protons. As a result, it will have an overall positive or negative charge.

The number of neutrons has no effect on the overall charge of the atom. Neutrons help give the nucleus of the atom stability. Even though we have already identified the correct answer, let’s thoroughly examine the other possible answers.

As we look at these answers, let’s consider an atom of the element fluorine with nine protons, 10 neutrons, and nine electrons. We know that it has nine protons because it has an atomic number of nine, which also tells us that, as a neutral atom, it will have nine electrons. Most fluorine atoms have 10 neutrons because the atomic mass of fluorine is very close to 19. Nine protons plus 10 neutrons equals an atomic mass of 19.

Choice (A), the number of electrons equals the number of neutrons, is incorrect. For one, this answer tells us nothing about the number of protons in the atom. So we don’t know if the negative charge of the electrons is balanced out by the positive charge of the protons. And in fact, the number of electrons doesn’t always equal the number of neutrons. For example, in our fluorine atom, there are nine electrons and 10 neutrons. So (A) is incorrect.

Choice (C) is incorrect for essentially the same reasons. Not only does this answer tell us nothing about how much of a negative charge there is to balance out the positive charge, there’s also not an equal number of neutrons and protons in many atoms. So choice (C) is also incorrect.

Our next incorrect answer is choice (D), the number of electrons and neutrons equals the number of protons. It does not make sense to combine electrons and neutrons and compare them to protons. Neutrons do not contribute any negative charge to the atom. So combining electrons and neutrons before comparing them to the number of protons does not accurately give us a picture of how the positive and negative charges of the constituent parts of the atom are balanced. While this choice does factor in both electrons and protons, the addition of neutrons makes it inaccurate. Also, we can compare the answer to our example atom of fluorine and see that the number of electrons and neutrons does not always equal the number of protons.

Our last incorrect answer is choice (E), the number of electrons plus protons equals the number of neutrons. Again, this choice incorporates both electrons and protons but in an inaccurate way. The total number of electrons and protons and the number of neutrons are irrelevant to the overall charge of the atom. Also, in our example atom of fluorine, there are 18 protons and electrons combined and only 10 neutrons. So this statement is not true for all atoms.

Overall, atoms have no overall charge because their positive charge and their negative charge are of equal strength because the positively charged particles and the negatively charged particles within them have the same strength of charge. The charges only canceled out when there’s the same number of particles of each type. So atoms do not have an overall charge because, answer (B), the number of electrons equals the number of protons.

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