Transcript Ch. 7 Sections 7.9 and 7.11 Powerpoint

Order of orbitals (filling) in multi-electron atom
Aufbau Principle:
an electron
occupies the
lowest-energy
orbital that can
receive it.
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s
Outermost subshell being filled with electrons
Why are d and f orbitals always in
lower energy levels?
• d and f orbitals require LARGE amounts of
energy
• It’s better (lower in energy) to skip a sublevel
that requires a large amount of energy (d and
f orbtials) for one in a higher level but lower
energy
This is the reason for the diagonal rule! BE SURE
TO FOLLOW THE ARROWS IN ORDER!
Electron configuration is how the electrons are distributed
among the various atomic orbitals in an atom.
number of electrons
in the orbital or subshell
1s1
principal quantum
number n
angular momentum
quantum number l
Orbital diagram
H
1s1
Shorthand Notation
• Step 1: Find the closest noble gas
to the atom (or ion), WITHOUT
GOING OVER the number of
electrons in the atom (or ion).
Write the noble gas in brackets [ ].
• Step 2: Find where to resume by
finding the next energy level.
• Step 3: Resume the configuration
until it’s finished.
What is the electron configuration of Mg?
Mg 12 electrons
1s < 2s < 2p < 3s < 3p < 4s
1s22s22p63s2
2 + 2 + 6 + 2 = 12 electrons
Abbreviated as [Ne]3s2
[Ne] 1s22s22p6
What are the possible quantum numbers for the last
(outermost) electron in Cl?
Cl 17 electrons
1s22s22p63s23p5
1s < 2s < 2p < 3s < 3p < 4s
2 + 2 + 6 + 2 + 5 = 17 electrons
Last electron added to 3p orbital
n=3
l=1
ml = -1, 0, or +1
ms = ½ or -½
Hund’s Rule: the lowest energy configuration
for an atom is the one having the maximum
number of unpaired electrons allowed by the
Pauli exclusion principle.
C 97
N
O
F
Ne
6
810
electrons
electrons
electrons
22s
222p
22p
5
246
3
Ne
C
N
O
F 1s
1s222s
Exceptions to the Aufbau Principle
• Remember d and f orbitals require LARGE
amounts of energy
• If we can’t fill these sublevels, then the next
best thing is to be HALF full (one electron in
each orbital in the sublevel)
• There are many exceptions, but the most
common ones are
d4 and d9
For the purposes of this class, we are going to
assume that ALL atoms (or ions) that end in d4
or d9 are exceptions to the rule. This may or
may not be true, it just depends on the atom.
Exceptions to the Aufbau Principle
d4 is one electron short of being HALF full
In order to become more stable (require less
energy), one of the closest s electrons will
actually go into the d, making it d5 instead of d4.
For example: Cr would be [Ar] 4s2 3d4, but since
this ends exactly with a d4 it is an exception to
the rule. Thus, Cr should be [Ar] 4s1 3d5.
Procedure: Find the closest s orbital. Steal one
electron from it, and add it to the d.
Keep an Eye On Those Ions!
• Tin
Atom: [Kr] 5s2 4d10 5p2
Sn+4 ion: [Kr] 4d10
Sn+2 ion: [Kr] 5s2 4d10
Note that the electrons came out of the
highest energy level, not the highest
energy orbital!