[Adam2126]

I don't fully understand why, when using short-hand notation to describe Fe's electron configuration, people use: [Ar] 3d(6)4s(2). 

I thought when writing electron configs you would use the last orbital, which in this case is 3d(6), rather than the last and second-to-last. On top of this, the last orbital comes before the second-to-last orbital? I do recall my chemistry teacher telling us that it is acceptable that if two orbitals with the same letter wind up being last, then you would use them, in order of coefficients, for short-hand notation. But this I do not understand, as the letters and numbers are different.

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Reply soon, and thank you for your time.

[Adam2126]

I don't fully understand why, when using short-hand notation to describe Fe's electron configuration, people use: [Ar] 3d(6)4s(2). 

I thought when writing electron configs you would use the last orbital, which in this case is 3d(6), rather than the last and second-to-last. On top of this, the last orbital comes before the second-to-last orbital? I do recall my chemistry teacher telling us that it is acceptable that if two orbitals with the same letter wind up being last, then you would use them, in order of coefficients, for short-hand notation. But this I do not understand, as the letters and numbers are different.

*{Mod Edit -- add useful title}*

Reply soon, and thank you for your time.

Okay, I figured out why they used [Ar], and know that it is convention to list the latest orbitals numerically, but I still fail to understand why that has to be done? Is 4s on a farther orbital than 3d?

[Borek]

Order in which they are listed doesn't matter, filling order is important. Notation is only a matter of convention.

Compare this recent thread: http://www.chemicalforums.com/index.php?topic=66441.0