|
ModifiedFrom-http://www2.asd.k12.ak.us/hauser/curriculum/html/Chemistry/Unit%209%20Modern%20Atomic%20Theory/Handouts%20and%20Notes/Unit_09_Light_(Handout).htm
Electron
configuratons and the periodic table
It will
be helpful now to look at electron configurations also
in the context of the periodic table. The
periodic table can be broken into “blocks” that show
what the last electron added to the electron
configuration is.
The
alkali metal electron configurations (group 1) always
end with “s1” and the alkaline earth
metals (group 2) always end with “s2”.
These 2 groups are know as “s
block” elements.
“P
block” elements are all those in groups 13-18 and
always end with 1 or more “p” electrons.
For example, all the elements in group 13,
beginning with boron, end with “p1”.
All of the elements in group 16, beginning with
oxygen, end with “p4”.
The transition elements are called
“d block” elements and always end with 1 or more
“d electrons”.
For example, the all of the elements in group 3
beginning with scandium, all end in “d1”.
The “f
block” elements are those at the bottom of
the periodic table that we call the lanthanide and
actinide groups. These
elements’ electron configurations always end with one
or more “f electrons.”
Practice
Your Electron Configurations-choose an element
It can
be very useful
to determine the last electron added (the
outermost electron) to any element since this will
always be a valence electron.
We can do this by looking at the periodic table
and finding 2 things: the period number (row number) and
the block that the element is contained in.
Let’s try this with the element calcium.
From a periodic table, we see it is in row
(period) 4 and we see that it is in the “s” block.
In fact calcium is
the second element in the “s” block, so the
last electron is an “s2” electron.
Since it is in period 4, the last electron added
is 4s2.
Now try finding the last electron added (the
outermost electron) to the element iodine.
We can see that it is in period 5 and in the “p”
block.
It is the 5th element in the “p”
block, so the last electron in iodine is 5p5.
One more example will show a break in the trend
we have set up. Find
the last electron in the element nickel.
We notice that it is in period 4 and it is the 8th
element in the “d” block.
We would think that it’s last electron would be
4d8, but in fact it is 3d8.
Remember that because of the orbital overlap we
talked about earlier, the “d orbital” principal
energy levels are always one behind the “s” and
“p” principal energy levels.
As a result, its electron configuration is [Ar]4s23d8
and the last electron added to nickel is a 3d8
electron. See
the following periodic table for these last electrons in
the electron configuration.
A few others are included so you can see the
patterns.

Next-->Hund's Rule
|