[rooksai]

The question is:
Which of the following possesses the highest energy electron?
A. Br-
B. Ca2+
C. Cr+
D. As

My attempt at the problem:
Br- has its last electron in the 4p6, which is [Ar]
Ca2+ has its last electron in the 3p6 level
Cr+ has its last electron in the 3d5 level, because regular Cr has electron config of [Ar]3d5 4s1
As has its last electron in the 4p3 level.

I answered C. But the book's answer is D. But I don't understand why because I thought by energy level from lowest to highest goes by this:
1s2 2s2 2p6, 3s2 3p6 4s2 4p6 3d10, which d has a higher energy level than p. Additionally, going by the book, As has its electron at the 4p3 suborbital
whereas, A has its electron at the 4p6 which is higher than 4p3. Please help me. Thank you!

[juanrga]

The question is:
Which of the following possesses the highest energy electron?
A. Br-
B. Ca2+
C. Cr+
D. As

My attempt at the problem:
Br- has its last electron in the 4p6, which is [Ar]
Ca2+ has its last electron in the 3p6 level
Cr+ has its last electron in the 3d5 level, because regular Cr has electron config of [Ar]3d5 4s1
As has its last electron in the 4p3 level.

I answered C. But the book's answer is D. But I don't understand why because I thought by energy level from lowest to highest goes by this:
1s2 2s2 2p6, 3s2 3p6 4s2 4p6 3d10, which d has a higher energy level than p. Additionally, going by the book, As has its electron at the 4p3 suborbital
whereas, A has its electron at the 4p6 which is higher than 4p3. Please help me. Thank you!

Why 10 electrons would have the same energy than 5?

[AbodunrinE]

The 4p orbital has higher energy than the 3d orbital by convention and so, electrons enter the 3d before going on further to occupy the 4p orbital. So instead of 1s2 2s2 2p6 4s2 4p6 3d10 it becomes 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2. problem solved.

[juanrga]

The 4p orbital has higher energy than the 3d orbital by convention and so, electrons enter the 3d before going on further to occupy the 4p orbital. So instead of 1s2 2s2 2p6 4s2 4p6 3d10 it becomes 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2. problem solved.

Cr violates the Madelung rule. For Cr and for Cr⁺ it is not (4s 3d) but (3d 4s).

[Ikana]

Hi and thanks for opening this topic!  

I've been studying General Chemistry for the MCAT and in my Princeton Review book I encountered a question that I could not understand or find help on understanding, hoping someone here can give me a hand.

Which of the following possesses the highest energy electron?

A) Br-
B) Ca2+
C) Cr+
D) As

I was thinking that Br- and As would both possess electrons of the same energy (the 4p level being their highest) and went with Br- because it has 4p6, which I thought would be higher than the 4p3 that As has.  The book lists As as the correct answer and I can't understand why.  I felt I understood what they were talking about, but still do not understand how it answers the question or why the question's answer is the way it is.  Your help is much appreciated!



Edit: Topics merged, redundant link removed. Dan