Difficulty: Hard

Average Score: 39%

What is the meaning of “–” when writing Cl⁻?

Rationale

The atom has gained an electron and now has a net negative charge.

The symbol Cl⁻ indicates that the chlorine atom has gained an extra electron, resulting in a net negative charge. This addition of an electron alters the overall electrical balance of the atom, leading to a negatively charged ion known as an anion.

A (The atom has gained a proton and now has a net positive charge.) YOUR ANSWER

Gaining a proton would increase the atomic number of chlorine, transforming it into a different element rather than forming an ion. Chlorine (Cl) cannot gain a proton without changing into a different element entirely, and thus cannot have a net positive charge in this context.

B (The atom has lost an electron and now has a net positive charge.) YOUR ANSWER

If the chlorine atom lost an electron, it would become positively charged (Cl⁺), not negatively charged. The presence of the negative sign in Cl⁻ indicates the opposite scenario, where the atom has indeed gained an electron rather than lost one.

C (The atom has gained an electron and now has a net negative charge.) CORRECT

This statement accurately describes the situation with Cl⁻. By gaining an electron, the chlorine atom achieves a negative charge, making it an anion. This is the fundamental definition of ionic charge, reflecting the balance of protons and electrons.

D (The atom has lost a proton and now has a net negative charge.) YOUR ANSWER

Losing a proton would decrease the atomic number of chlorine, which would not result in a net negative charge but rather change the identity of the element. An atom cannot lose a proton and retain its elemental identity while becoming negatively charged; it would need to gain electrons to achieve that state.

Conclusion

The notation Cl⁻ signifies that the chlorine atom has gained an electron, which results in a net negative charge, thus forming an anion. Understanding ionic charges is crucial in chemistry, as it impacts reactivity and bonding behavior. The incorrect choices misinterpret the fundamental relationship between protons and electrons in determining the charge of an atom.

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