Transcript Introduction to Electron Configurations

Quantum Theory and the
Electronic Structure of Atoms
Part 2
Unit 4, Presentation 1
QUANTUM NUMBERS
The shape, size, and energy of each orbital is a function
of 3 quantum numbers which describe the location of
an electron within an atom or ion
n (principal)
---> energy level
l (orbital) ---> shape of orbital
ml (magnetic) ---> designates a particular
suborbital
The fourth quantum number is not derived from the
wave function
s (spin)
---> spin of the electron
(clockwise or counterclockwise: ½ or – ½)
Schrodinger Wave Equation
Y = fn(n, l, ml, ms)
principal quantum number n
n = 1, 2, 3, 4, ….
distance of e- from the nucleus
n=1
n=2
n=3
Where 90% of the
e- density is found
for the 1s orbital
e- density (1s orbital) falls off rapidly
as distance from nucleus increases
Types of Orbitals (l)
s orbital
p orbital
d orbital
l = 0 (s orbitals)
l = 1 (p orbitals)
p Orbitals
this is a p sublevel
with 3 orbitals
These are called x, y, and z
3py
orbital
p Orbitals
• The three p orbitals lie 90o apart in
space
l = 2 (d orbitals)
f Orbitals
For l = 3,
orbitals
f sublevel with 7
Schrodinger Wave Equation
Y = fn(n, l, ml, ms)
magnetic quantum number ml
for a given value of l
ml = -l, …., 0, …. +l
if l = 1 (p orbital), ml = -1, 0, or 1
if l = 2 (d orbital), ml = -2, -1, 0, 1, or 2
orientation of the orbital in space
ml = -1
ml = -2
ml = 0
ml = -1
ml = 0
ml = 1
ml = 1
ml = 2
Schrodinger Wave Equation
Y = fn(n, l, ml, ms)
spin quantum number ms
ms = +½ or -½
ms = +½
ms = -½
Energy of orbitals in a single electron atom
Energy only depends on principal quantum number n
n=3
n=2
n=1
Energy of orbitals in a multi-electron atom
Energy depends on n and l
“Fill up” electrons in lowest energy orbitals (Aufbau principle)
The most stable arrangement of electrons in
subshells is the one with the greatest number of
parallel spins (Hund’s rule).
Order of orbitals (filling) in multi-electron atom
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s
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
What is the electron configuration of Mg?
Mg
What are the possible quantum numbers for the
last (outermost) electron in Cl?
Cl
Outermost subshell being filled with electrons
Paramagnetic
unpaired electrons
2p
Diamagnetic
all electrons paired
2p
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.
Try These!
• Write the shorthand notation
for:
Cu
Ag
Cu
Keep an Eye On Those Ions!
• Electrons are lost or gained like they
always are with ions… negative ions
have gained electrons, positive ions
have lost electrons
• The electrons that are lost or gained
should be added/removed from the
highest energy level (not the highest
orbital in energy!)
Keep an Eye On Those Ions!
• Tin
Atom:
Sn+2 ion:
Sn+4 ion:
Note that the electrons typically came
out of the highest energy level, not the
highest energy orbital!