# Problem: Rank the following items in order of decreasing radius: Mg, Mg2+ , and Mg2−The size of ions as measured by ionic radii varies in a systematic manner. The size of the ion can be explained in part by effective nuclear charge, Zeff, which is the net nuclear charge felt by an electron. The effective nuclear charge takes into account the actual nuclear charge and the shielding of this charge by inner electrons. When an atom loses electrons, the resulting cation is smaller both because the remaining electrons experience a larger Zeff and because these electrons are usually in orbitals closer to the nucleus than the electrons that were lost. The more electrons that are lost, the smaller the ion becomes. Similarly, when an atom gains electrons, the resulting anion is larger owing to both increased electron-electron repulsions and a reduction in Zeff. The more electrons that are gained, the larger the ion becomes.

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Rank the following items in order of decreasing radius: Mg, Mg2+ , and Mg2−

The size of ions as measured by ionic radii varies in a systematic manner. The size of the ion can be explained in part by effective nuclear charge, Zeff, which is the net nuclear charge felt by an electron. The effective nuclear charge takes into account the actual nuclear charge and the shielding of this charge by inner electrons. When an atom loses electrons, the resulting cation is smaller both because the remaining electrons experience a larger Zeff and because these electrons are usually in orbitals closer to the nucleus than the electrons that were lost. The more electrons that are lost, the smaller the ion becomes. Similarly, when an atom gains electrons, the resulting anion is larger owing to both increased electron-electron repulsions and a reduction in Zeff. The more electrons that are gained, the larger the ion becomes.

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Periodic Trends: Ionic Radius concept. You can view video lessons to learn Periodic Trends: Ionic Radius. Or if you need more Periodic Trends: Ionic Radius practice, you can also practice Periodic Trends: Ionic Radius practice problems.

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Based on our data, we think this problem is relevant for Professor Davis & Chen's class at McMaster University.