electron configuration

how would the 7 electrons of a particular atom be configured amongst its
shells? i cant seem to remember this stuff and need someones help to resolve
an argument. my friend thinks that there would be 2 electrons in the first
shell, and a total of 5 in the second.

i agreed with this at first, but remember hearing that there has to be
either 8 or 2 electrons in the outer shell, so i make the configuration to
be 2 in the first, 3 in the second and 2 in the third.

can anyone shed some light?

Your friend is right.
In the first shell (1s): two electrons, ms = 1/2, -1/2
In the second shell (2s and 2p): two electrons with l=0 and ms = 1/2, -1/2
and 6 with l = 1, m = 1,0,-1 and ms = 1/2, -1/2
So together the two lowest shells can contain 8 electrons.

"Jeremy Watts" <[Only registered users see links. ]> skrev i meddelandet
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"Mattias" <m.h@t.c> wrote in message
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2+2+6=10

-Neon-


Tom Davidson
Brighton, CO

"Jeremy Watts" <[Only registered users see links. ]> wrote in message
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Presumably you are discussing nitrogen...


Did you forget that the *inner* shells get filled first?

Two electrons go into the first shell (2*1^2), the 1S shell.

The second shell has *room* for 8 electrons (2*2^2) [2 in the 2S subshell
and 6 in the 2P subshell]. The third has room for 18 electrons (2*3^2), [2
in the 3S, 6 in the 3P, and 10 in the 3D subshells], and so on. The actual
*energy* of these shells and subshells is more complicated, however, so they
don't always fill in a simple order. For example, the 4S subshell electrons
[potassium, calcium] have lower energy than the 3D subshell electrons
[scandium, titanium, etc] , so they get placed first.

Back to your simple case, a nitrogen *atom* has only 7 electrons, of which 5
sit in a shell [the 2 shell, including the 2S and 2P subshells] which would
be satisfied with 8. Nitrogen will then "look around' for electrons on
other atoms to share. If it finds another nitrogen atom, each will share 3
of their own electrons with the other, forming 3 electron pairs shared
between two atoms (called "chemical bonds"). Each nitrogen then has 2 of
its own electrons in the 2S subshell and 6 shared electrons in the 2P
subshell. That makes 3 bonds between the two atoms, which makes the
nitrogen *molecule* N2 very stable and unreactive.


Tom Davidson
Brighton, CO