An atom contains a total of 25 electrons. When the atom is in the ground state, how many different principal energy levels will contain electrons?
Answers
Well, with
25
electrons, whatever atom it is, it need not be neutral... but since it's within the neighborhood of a transition metal, we can assume it's one of them... i.e. it may be
Mn
, or perhaps
Co
2
+
.
With
25
electrons, we can immediately write the electron configuration. Argon has
18
electrons and is the previous noble gas, and thus we use it as the noble gas core.
1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
3
d
5
4
s
2
→
[
A
r
]
3
d
5
4
s
2
And you can convince yourself that
18
+
5
+
2
=
25
electrons total.
This lands us in the first-row transition metals, and so we have involved
n
=
1
,
2
,
3
,
and
n
=
4
. Those are the only principal energy levels involved... These contain the following orbitals:
n
=
1
:
1
s
n
=
2
:
2
s
,
2
p
n
=
3
:
3
s
,
3
p
,
3
d
n
=
4
:
4
s
We ignore the
4
p
,
4
d
,
4
f
obviously because they are empty.
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