Number of Period = Row number in table, so it concerns Li to Ne...
4 Quantum numbers:
n = Principal number (basically row number);
#l# ## = Azimuthal (Orbital) number;
m = Magnetic number;
s = Spin number.
Maximum values:
n = 1,2,3,4,5 etc. (remember, this is the row number)
#l# ranges from 0 to n-1.
m ranges from #-l""# to #+l#
If n =1 (row 1) then #l# can only be 0. (n-1 = 1-1 = 0)
If #l#=0 then m can only be 0. (#-l""# to #+l # )
s is always either -1/2 or +1/2
This describes the #1S#-orbital, with max. 2 #e^-# in it.
If n=2, then #l# ranges from 0 to n-1, which is 1.
Once again:
If #l#=0 then m can only be 0. (#-l""# to #+l # )
s is always either -1/2 or +1/2
since n=2, this describes the #2S#-orbital, with max. 2 #e^-# in it.
If however #l#=1 then m can be #color(red)"-1, 0 or 1"# (#-l""# to #+l # )
#l# = 1 describes the #P#-orbital, or rather set of:
m=-1: #rarr P_x#
m=0: #rarr P_y#
m=+1: #rarr P_z#
Therefore, in period 2 there are 4 orbitals: #2S, 2P_x, 2 P_y # and #2P_z#
2 electrons in each orbital: #rarr# 4 x 2 = 8 #e^-#...
The #2S#-orbital (S for Spherical) has a larger diameter than the #1S#, and therefore completely envelopes it.
Hence the two #e^-# of the #1S# are sheltered and play no part in normal reactions. They are therefore not Valence Eectrons.
