Hello! I have a question that asks what will the electron configurationfor Cr (a

Question

Hello!

I have a question that asks what will the electron configurationfor Cr (atomic number 24) be if it lost 3 electrons?

The correct answer is [Ar] 3d3

My thinking is this: I know that 4S fills before 3D. But it did notin this case. Also, I thought when electrons are lost, they losefrom the highest energy level number first, which is 3D in thiscase. So, if Cr goes from atomic number of 24 to 21, 3 electronsshould lose from the 3D quantam. But, why would it take away 3electrons from the 3D if the 4S has not been filled yet?

I am confused.

If someone can answer this in the simplest way, I will be gratefuland rate high.

Explanation / Answer

This is a weird case that happens with many elements but it isbasically because the orbitals are more stable if they are moresymmetrical. Cr is a poor example of this and thereforeconfusing. Emptying the 4s orbital first will allow moreelectrons to be in the 3d so it can be more stable. You willalso see elements strive for half orbitals some times in onesometimes in both the 4s and 3d. Such as Fe2+ willlose electrons from both the s and d orbital, one from each sothere is 1 left in the s and 5 left in the d which will half fillthem both. If it turns into the Fe3+ ion then thelast electron in the s orbital will be lost not a d orbitalelectron. Good Luck

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