Mr. Shields
Regents Chemistry
U06 L04
1
Quantum Mechanical Atom
Let’s review the orbital structure of the
Quantum Mechanical model of the atom:
Quantum
no.
No. of
Sublevels
Sublevels
No. of
orbitals
1
1
s
1
2
2
s, p
1, 3 = 4
3
3
s, p, d
1, 3, 5 = 9
4
4
s, p, d, f
1, 3, 5, 7 = 16
5
4
s, p, d, f
1, 3, 5, 7 = 16
6
4
s, p, d, f
1, 3, 5, 7 = 16
7
4
s, p, d, f
1, 3, 5, 7 = 16
2
Energy levels
As “n” increases Energy increases
n=1 2 3 4 5 6 7
E
As sublevels progress from s to p to d to f
Energy also increases
s p d f
E
3
Electron Orbital filling
This increasing energy sequence defines
Into which Orbitals electrons go as they
are added to the atom .
The lowest energy levels fill first according
To certain specific rules.
Remember Rubidium that we looked at earlier?
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Sublevel
Energy increases
From s to f.
Some sublevels
With a lower n may
Actually be at a
Higher energy level
Than some ein a higher n !
4f > 5s,5p,6s
4d > 5s
3d > 4s
5
Orbital Filling Rules
Rule 1: The Aufbau Principle
Each electron occupies the lowest energy orbital first
- all orbitals in the same energy sublevel are of
equal energy
- ex: electrons in 2px, 2py, 2pz al have the same
energy
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Orbital Filling Rules
Rule 2: The Pauli exclusion Principle
Each atomic orbital can only hold a max of 2 electrons
- ex: the three p orbitals can each hold 2 electrons
so the p sublevel has 6 electrons
How many electrons are in the s, d and f sublevels?
7
Orbital Filling Rules
Rule 3: Hund’s rule
If there is more than 1 sublevel orbital each is filled with
One electron before a second is added to each until
The sublevel orbitals are filled.
- ex:
2px
2py
2pz
8
Electron nomenclature
Look at Carbon. It’s atomic # is 6 so it has 6 electrons.
According to the rules of
orbital filling, it’s electrons
Would occupy these orbitals.
If we wanted to write this electron
configuration it would be written
as follows:
1s2 2s2 2p2
2-4
Atomic No. 6
Or we could condense this further and write “2-4” as it is
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Written in your reference tables.
How would we write the electron figuration
For these two elements?
Atomic # = 7
1s2
2s2
or
2-5
2p3
Atomic # = 8
1s2 2s2 2p4
or
2-6
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Electronic structure of the Excited State
Atomic # = 7
Atomic # = 8
What are the ground states?
1s2 2s2 2p3
1s2 2s2 2p4
One possible excited state (out of many) might be
1s2 2s1 2p33s1
1s1 2s2 2p5
Can you think of other possible excited states?
11
Kernal Nomenclature
Look at the electron configuation of Chlorine ( 2-8-7 ) and
Neon ( 2-8 ).
In the Kernal, or Noble gas, format for designating electron
config we write the electron configuration of the atom by:
1) Writing the symbol of the PRECEDING noble gas
element in brackets
1) After skipping the electron configuration portion common
to both the nobel gas and the atom in question write out
the electron configuration of the residual electrons. These
should be the outermost principle energy level electrons.
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Kernal Nomenclature
For example chlorine would be represented as [Ne] 3s23p5
Or [Ne] 7. [Ne] designates the 2-8 portion of the electron
structure of Chlorine (2-8-7).
What’s the noble gas (i.e Kernal) configuration for C?
[He] 2s22p2
or simply
(Quantum desc.)
[He] 4
(Bohr desc.)
What is the kernal (noble gas) configuration for the
following (use both formats (Quantum and Bohr):
K
P
13
Valence Electrons
Electrons in the outermost principal energy levels are called
VALENCE ELECTRONS
For the representative elements the valance electrons
represent the s and/or p orbitals
How many valence electrons do the following atoms have?
Li
1
F
7
Ne
8
and what about these…
Na
1
Cl
7
Ar
8
notice anything peculiar?
14
Look at the 1st three periods of the periodic table
As we move from left to right we add electrons one at a time
Valence shell
1e
2e
3e
4e
5e
6e
7e
8e
Electrons in the outermost Principal energy level are known as –
Valence electrons; the orbit they’re in is known as the valence 15
shell
Valence Electrons
What do you notice about the number of
Electrons in the valence shell of the Noble
Gas elements? (i.e. He Ne Ar Kr Xe Rn)
Their outermost shell is full and accept for helium
they all have 8 electrons.
Why doesn’t helium have 8 electrons?
16
The Octet Rule
The electron configuration of 8 electrons in
The outermost principle energy level is
A VERY STABLE electron configuration.
It’s know as the OCTET RULE
Atoms strive to attain this electron configuration
(ns2 np6) by gaining or losing electrons
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The Octet Rule
For example the electron configuration for
Sodium is: 1s2 2s2 2p6 3s1
2-8-1
If sodium loses one electron to become an
Ion (Na -1e  Na+) it’s remaining electrons
have the Electron config of Ne (2-8).
It’s outermost Energy level now has an octet!
18
Same electron
Config as Ne
Sodium
19
The Octet Rule
Let’s next look at the electron config of Cl
1s2 2s2 2p6 3s2 3p5 or 2-8-7
If Cl gains one electron to become an ion
(Cl +1e  Cl-) the electron configuration
Will have the Electron config of Ar (2-8-8).
20
Lewis Dot Structures
Valence electrons are very important
In Chemical compound formation so it
helps if we can indicate these electrons
Schematically
These drawings are called LEWIS DOT
STRUCTURES. They are created by placing
The valence electrons around the elements
Symbol.
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Lewis Dot Structures
It easy if you think of an imaginary box
surrounding the symbol
N
Valence Electrons are added as
dots at the Center-points of the box lines,
one at a time Filling the s Orbital first.
These electrons are the atom’s valance
Electrons, specifically the s & p electrons.
What is the max no. of electrons
possible?
8
Ne
Mg
N
22
Lewis dot structures of Ions
Atoms gain or lose electrons to try to
Achieve the octet structure.
They then become ions.
Na -1e  Na
+
(a cation)
Br +1e  Br
-
(an anion)
In removing an electron
From sodium we empty the valence shell and when we add
An electron to Bromine we fill the valence shell.
In both cases, what is left is the OCTET
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Lewis dot structures of Ions
Lewis Dot structures for ions look the same as they do for
Atoms except brackets are used:
[ Na ]+ or just Na+
Notice there are no electrons
shown as dots. That’s
because Na has emptied it’s
Valence shell
On the other hand, Br filled it’s valence shell. It now
Has 8 electons. It’s Lewis dot structure shows these
electrons:
[ : Br : ] 24
Write the Lewis dot structures for:
Al, Al+3, P, I-, S and S-2
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