Representative Elements
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Representative Elements

Remember from the earlier review of electron configurations that H, Li and Na all ended with s1. If you look at the rest of the elements in that group you will see that the similarity continues on down the periodic table. All of the elements in group Ia end in s1 for their electron configuration. What is different about them is which level of s1 they end with.

Notice also that this periodic table only shows the last part of the electron configuration. The reason for this is that the chemical properties of an element are determined by the outermost electron structure. So this periodic table was prepared with just those outermost electron configurations written on it.

Ia
H   1s1
Li   2s1
Na   3s1
K   4s1
Rb   5s1
Cs   6s1
Fr   7s1

 

Now look at group IIa, all of them end in s2 but a different s2 for each one: 2s2 for beryllium, 3s2 for magnesium, and so on. Next, what comes after the s sublevel is filled? If we go one electron past magnesium, we get aluminum. Its outermost electron configuration is 3s23p1. Notice that if you look above and below aluminum, all of the outermost electron configurations for this group of elements have the same pattern. What is different is which period they are in. Boron is 2s22p1. Aluminum is 3s23p1. Gallium is Ga and is an element you didn't have to memorize, but from its position on the periodic table, you can see that it is 4s24p1. And so on, on down.
IIa IIIa
Be   2s2 B   2s22p1
Mg   3s2 Al   3s23p1
Ca   4s2 Ga   4s24p1
Sr   5s2 In   5s25p1
Ba   6s2 Tl   6s26p1
Ra   7s2  

 

If you keep going to the right on the periodic table, notice how with each column there is one more p electron in each of the energy levels, right over to the inert gases.
B
2s22p1
C
2s22p2
N
2s22p3
O
2s22p4
F
2s22p5
Ne
2s22p6
Al
3s23p1
Si
3s23p2
P
3s23p3
S
3s23p4
Cl
3s23p5
Ar
3s23p6
Ga
4s24p1
Ge
4s24p2
As
4s24p3
Se
4s24p4
Br
4s24p5
Kr
4s24p6
In
5s25p1
Sn
5s25p2
Sb
5s25p3
Te
5s25p4
I
5s25p5
Xe
5s25p6
Tl
6s26p1
Pb
6s26p2
Bi
6s26p3
Po
6s26p4
At
6s26p5
Rn
6s26p6
 

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