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Postby elliekauffman1I » Tue Nov 07, 2017 8:39 pm

Why, for part A, does [Ar]3d6 cause the answer to be Co3+? Same for part B with Fe3+? On 3.9 when we had 3d6, the answer involved Fe, but on this one 3d6 involved Co. I'm confused as to why this is.

Hannah Chew 2A
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Re: 3.11

Postby Hannah Chew 2A » Tue Nov 07, 2017 9:50 pm

The difference between 3.11 and 3.9 is that 3.11 is talking about a 3+ cation whereas 3.9 is talking about a 2+ cation. For 3.11A, we need to find an element with the configuration [Ar]3d74s2. A parent atom loses 3 valence electrons to form a cation, so going from a cation to a parent atom means that we must add 3 electrons. Therefore, the parent must have the configuration [Ar]3d74s2. The same process can be said about 3.11B.

Leah Savage 2F
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Re: 3.11

Postby Leah Savage 2F » Fri Nov 10, 2017 11:54 am

[Ar] 3d6 for an 3+ cation means that 2 4s valence electrons plus one d electron were taken away. This makes sense for Co, which normally is 3d7 4s2. Two 4s electrons and one d electron was taken away from Co3+. For Fe 3+, two 4s electrons and 1 d electron were taken away leaving 3d5, so this must be Fe, which normally is 3d6 4s2.

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Re: 3.11

Postby AtreyiMitra2L » Sat Nov 25, 2017 1:02 pm

Electrons are removed from the outer most energy sub shell. In Co, the electron configuration would be [Ar]3d74s2. Because the cobalt is now Co 3+, 3 electrons are removed. The first 2 are removed from 4s2. The next outermost sub shell is 3d7. So now its just 3d6. In number 9, note that we are only removing 2 electrons not 3.

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