## 6th edition chapter 3 problem 9

Karina Vasquez 1D
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### 6th edition chapter 3 problem 9

Which M^2+ ions (where M is a metal) are predicted to have the following ground-state electron configurations: (a) [Ar]3d7; (b) [Ar]3d6

I don't understand how to begin finding M because are the 2+ electrons lost already or do we apply it to the following? Assuming its the latter would I take from 4s^2?

Chem_Mod
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### Re: 6th edition chapter 3 problem 9

According to the Aufbau principle, the 4s sublevel is filled up before the 3d sublevel because the 4s sublevel is lower in energy so electrons in the 4s sublevel would be lost first. An ion with a +2 charge has loss two electrons, so its configuration would have two less electrons than it would have if it did not have a +2 charge. Co+2 would have the configuration in (a) and Fe+2 would have the configuration in (b).

hannabarlow1A
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### Re: 6th edition chapter 3 problem 9

I had trouble with this question too, until I realized the subshells we were dealing with. With the 4s vs. 3d subshells, electron configurations do not follow the typical "protocol." It takes less energy for electrons to join the 4s orbital and also to leave it, so the +2 charge means that 2 electrons are lost from 4s, not 3d.