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Unformatted text preview: of electrons it has, but unfortunately, the number of electrons for
an atom is subject to change.
Fortunately, for an element only (this is no longer true when the element becomes part of
a compound), the total number of electrons is exactly equal to the total number of protons.
What’s more, the number of protons is not subject to change. Thus, we identify an element
according to the number of protons it has; we call this it’s “atomic number.”
Electrons are not bound by the laws of classical physics; they follow their own laws as
delineated by Quantum Mechanics. Although we will never be able to fully understand these
quantum laws (since we are classical creatures), we can learn from the lessons they provide. (1)
Electrons will fill shells in order from the first shell, to the second, and onwards until all
electrons are accounted for. (2) Each shell has a set of subshells equal to the number of subshells
from the previous shell plus one; that is, the first shell has only the “1s” subshell, the second
shell has the “2s” and “2p” subshells, the third shell has the “3s”, “3p” and “3d” subshells, the
fourth shell has the “4s”, “4p”, “4d” and “4f” subshells, and so on. (3) Each type of subshell has
a set of orbitals equal to the number of orbitals of the previous subshell plus two more. That is,
there is always only 1 “s” orbital, but there are 3 “p” orbitals, 5 “d” orbitals, 7 “f” orbitals, etc.
(4) Each orbital can hold exactly two electrons, provided they are in opposite “spin.” Thus, in
any given shell, there are a maximum of 2 “s” electrons, 6 “p” electrons, 10 “d” electrons and 14
Part I: Electronic Configuration of the Elements
Dakota State University Page 93 of 232 Experiment 7: Quantum Mechanics General Chemistry I and II Lab Manual The Aufbau process tells us what subshells (s, p, d, or f) are present in any given
shell. Begin by drawing out a diagram of each shell and all associated sub shells with that shell,
being very careful to keep consistent spacing both horizontally and vertically. Then draw angled
lines through them beginning from the 1s orbital through the remainder of the diagram. Then
simply read off the order of filling beginning from the first line and going through diagonally
down each line from the upper right to lower left until you’ve gone as far as needed.
From this diagram we see that the
order of filling is 1s 2s 2p 3s 3p 4 s 3d 4p
5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p, which is
as far as the periodic chart goes. Take a
careful look at the periodic chart with this
filling order and follow it along to see
how it corresponds.
Once we know the order of filling, we can
simply fill in the electrons, remembering
of course the number of electrons each
element can hold, until we’ve accounted for all of the electrons in the element, even if we are
looking for an element that is beyond those that have been discovered to date!
Remembering the number of electrons each subshell can hold, and the subshells present
for each shell, fill out the following table for the entire periodic chart. (One example has been
12 Electronic Configuration H
Mg Dakota State University Page 94 of 232 Experiment 7: Quantum Mechanics 13
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