Advanced Chemistry Unit 6
Quantum Mechanics

Advanced Chemistry Unit 6
Quantum Mechanics
Things aren’t always as they seem…

Remember,
Protons determine which element it is ….
But Electrons determine what an element will do!
In this unit, we will take a closer look at how electrons behave…..Quantum Mechanics

This is the model of the atom developed by Niels Bohr.
• It shows the electrons orbiting the nucleus in circular paths
(1885-1962)

In the Bohr model, the valence electrons (the electrons involved in chemical bonding) are shown in the outer ring
Sometimes we use this model to help us imagine how one atom can transfer an electron to another atom
(ionic bonding)

In this model, the valence electrons (the electrons involved in chemical bonding) are shown in the outer ring
Sometimes we use this model to help us imagine how one atom can share electrons with another atom
(covalent bonding)

Bohr model of a helium atom
A more realistic model of where the electrons are in a Helium atom
The Bohr model works very well for many things, but it really doesn’t show the true complexity of the atom.
In this chapter, we’re going to think about atoms, specifically their electrons, in a more complex way.

What do we know about electrons ?
Electrons are moving around the nucleus at very high velocity – not necessarily in circular orbits
Two hydrogen atoms combining to form one H
2 molecule
The electrons move so fast that it would look like an electron cloud

Within the electron cloud, there are areas where you are more likely to find an electron and areas where finding an electron is less likely.
Mathematicians call this “probability”
An area where you are likely to find electrons is called an orbital.
We will look at the different types of orbitals in a moment. But first, an analogy.

The boarding house analogy:
A boarding house has many beds, in various floors and rooms.
Each bed has its own designation, or address
(the manager’s code)

The boarding house analogy – what’s the filling pattern?

What is the order in which the beds get filled?
How does the manager keep track of which bed each guest is assigned to?
We can think of electrons in a similar way.
Electrons will have electron “address” that will tell us where in the atom are located.

s orbitals
An s orbital can hold two electrons

p orbitals
Each p orbital can hold two electrons
There are three variations of bowtie shaped p orbitals
(the difference between them is their orientation in space, like the x, y, and z axes on a graph)

d orbitals
d orbitals really have interesting shapes……
“double dumbells”
…and a “dumbell with a donut”!
No, you don’t have to remember these shapes

f orbitals
No, you don’t have to remember these shapes either

If an atom has several orbitals, you can see how they overlap, making the “electron cloud” have areas where it is more likely to find electrons

Ok, this is complicated…
What do I really need to know about electron orbitals?
Orbitals are areas where electrons are likely to be found
Orbitals have different shapes (s=sphere, p=bowtie)
The more electrons an atom has, the more places (orbitals) it will need to hold the electrons
Showing where the electrons are located is like a game, and it is easy if you follow the rules….






Determine the number of electrons in the atom or ion
Start with the 1s orbital and fill each orbital according to the guide (Aufbau principle)
Show each electron as an arrow
Add arrows (electrons) individually to the boxes until all electrons in the atom have been drawn
Follow Hund’s rule and Pauli’s principle
(more on this as we do the practice atoms)

7s
6s
5s
4s
3s
2s
1s
7p
6p
5p
4p
3p
2p
6d
5d
4d
3d
Each box can hold 2 electrons
5f
4f


Aufbau Principle-
“building up” an electron occupies the lowest-energy orbital that can receive it
This means start from the 1s and work your way upwards until you use all of electrons

Phosphorus
15 electrons
For neutral atoms, the number of electrons is the same as the number of protons
Let’s put them in the proper places on the orbital notation diagram

7s
6s
5s
4s
3s
2s
1s
7p
6p
6d
5f
5d
5p
4d
4f
4p
3p
2p
3d
Phosphorus
(15 electrons)

The first two electrons go into the 1s orbital

Notice the opposite arrow directions*

13 more electrons to go

7s
6s
5s
4s
3s
2s
1s
7p
6p
5p
4p
3p
2p
6d
5d
4d
3d
Phosphorus

The next electrons go into the 2s orbital

11 more to go
5f
4f

7s
6s
5s
4s
3s
2s
1s
7p
6p
5p
4p
6d
5d
4d
3d
5f
4f
3p
2p
Phosphorus
•
The next 6 electrons go into the 2p orbital
•
One up arrow and one down arrow per box
• Fill separately before you double up in the same box
• only 5 more to go

7s
6s
5s
4s
3s
2s
1s
7p
6p
5p
4p
3p
2p
6d
5d
4d
3d
Phosphorus
•
The next 2 electrons go into the 3s orbital
5f
4f
• only 3 more to go

7s
6s
5s
4s
3s
2s
1s
7p
6p
6d
5f
5d
5p
4d
4f
4p
3d
3p
2p
Phosphorus
• The last three electrons go into the 3p orbitals.
• They each go into separate boxes*
• They each show an “up” arrow*

7s
6s
5s
4s
3s
2s
1s
7p
6p
5p
4p
3p
2p
6d
5d
4d
3d
Phosphorus
The electron configuration for Phosphorus is
1s 2 2s 2 2p 6 3s 2 3p 3
5f
4f

Why did we put one arrow up and one arrow down in each box?
Pauli Exclusion Principlejust like no two houses can have the same address, no two electrons in the same atom can have the same “address”. If there are two electrons in the same orbital, we need to make one and the other
(by tradition, we write the up arrow first)

When we filled the p orbitals, why did we put one arrow in each box before putting two in the same box?
Hund’s Ruleorbitals of equal energy are each occupied by one electron before any orbital is occupied by a second
(fill each energy level separately before you double up)

The electron configuration for Phosphorus is
1s 2 2s 2 2p 6 3s 2 3p 3

http://www.youtube.com/watch?v=Vb6kAxwSWgU

Orbital Diagrams and
Electron Configuration ws
1-12

Manganese
25 electrons
For elements, the number of electrons is the same as the number of protons
Let’s put them in the proper places on the orbital notation diagram

7s
6s
5s
4s
3s
2s
1s
7p
6p
6d
5f
5d
5p
4d
4p
3p
2p
3d
Manganese
(25 electrons)

The first two electrons go into the 1s orbital

Notice the opposite arrow directions*
4f

7s
6s
5s
4s
3s
2s
1s
7p
6p
5p
4p
3p
2p
6d
5d
4d
3d
Manganese

The next electrons go into the 2s orbital
5f
4f

7s
6s
5s
4s
3s
2s
1s
7p
6p
5p
4p
6d
5d
4d
3d
5f
4f
3p
2p
Manganese
•
The next 6 electrons go into the 2p orbital
•
One up arrow and one down arrow per box

7s
6s
5s
4s
3s
2s
1s
7p
6p
5p
4p
3p
2p
6d
5d
4d
3d
Manganese
•
The next 2 electrons go into the 3s orbital
5f
4f

7s
6s
5s
4s
3s
2s
1s
7p
6p
6d
5d
5f
5p
4d
4p
3d
3p
Manganese
2p
• The next six electrons go into the 3p orbitals.
• That makes 18 electrons done…and 7 more to go
4f

7s
6s
5s
4s
3s
2s
1s
7p
6p
6d
5d
5f
5p
4d
4p
3d
3p
Manganese
2p
• The next two go into the
4s orbital
• 20 electrons done…..
5 to go
4f

7s
6s
5s
4s
3s
2s
1s
7p
6p
6d
5d
5f
5p
4d
4f
4p
3d
3p
Manganese
2p
• The final five electrons go into the 3d level

7s
6s
5s
4s
3s
2s
1s
7p
6p
5p
4p
3p
6d
5d
4d
3d
Manganese
2p
The electron configuration for Manganese is
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5
5f
4f

Let’s try some more
Li
Be
B
C
N
O
F
Ne
This time we’ll save space and show the boxes as lines instead

Element
Lithium
(3e )
Electron
Configuration
1s 2 2s 1
Beryllium
(4e )
1s 2 2s 2
Boron
(5e )
1s 2 2s 2 p 1
1s 2 2s 2 p 2 Carbon
(6e )
Nitrogen
(7e )
1s 2 2s 2 p 3
Oxygen
(8e )
1s 2 2s 2 p 4
Fluorine
(9e )
1s 2 2s 2 p 5
Neon
(10e )
1s 2 2s 2 p 6
Orbital notation (arrows)
____ ____ ____ ____ ____
1s 2s 2p
____ ____ ____ ____ ____
1s 2s 2p
____ ____ ____ ____ ____
1s 2s 2p
____ ____ ____ ____ ____
1s 2s 2p
____ ____ ____ ____ ____
1s 2s 2p
____ ____ ____ ____ ____
1s 2s 2p
____ ____ ____ ____ ____
1s 2s 2p
____ ____ ____ ____ ____
1s 2s 2p

Valence electrons- the electrons involved in chemical bonding…..
…how are these determined?

Valence Electrons


Valence electrons are the electrons in the outermost energy level
These are the electrons that determine if/how an atom will bond with other atoms
1s 2s 2p 3s 3p
Silicon has
4 valence electrons

Valence Electrons
How many valence electrons does Chlorine have?
1s 2s 2p 3s 3p

Valence Electrons
Can you locate the valence electrons in this atom of Cobalt ?


Valence electrons are the electrons in the outermost energy level
These are the electrons that determine if/how an atom will bond with other atoms

Valence Electrons
How many valence electrons does Bromine have?

Valence Electrons
How many valence electrons does a Bromine ion have?

Element
Lithium
(3e )
Electron
Configuration
1s 2 2s 1
Beryllium
(4e )
1s 2 2s 2
Boron
(5e )
1s 2 2s 2 p 1
1s 2 2s 2 p 2 Carbon
(6e )
Nitrogen
(7e )
1s 2 2s 2 p 3
Oxygen
(8e )
1s 2 2s 2 p 4
Fluorine
(9e )
1s 2 2s 2 p 5
Neon
(10e )
1s 2 2s 2 p 6
Orbital notation (arrows)
____ ____ ____ ____ ____
1s 2s 2p
____ ____ ____ ____ ____
1s 2s 2p
____ ____ ____ ____ ____
1s 2s 2p
____ ____ ____ ____ ____
1s 2s 2p
____ ____ ____ ____ ____
1s 2s 2p
____ ____ ____ ____ ____
1s 2s 2p
____ ____ ____ ____ ____
1s 2s 2p
____ ____ ____ ____ ____
1s 2s 2p

What are the electron configuration patterns for different families of elements?
Is there an overall pattern?
Chalcogens

Electron Configuration for Alkali Metals


Electron configuration end in s 1
Outer level has 1 valence electron
Example: Sodium
1s 2s
1s 2 2s 2 2p 6 3 s 1
2p 3s

Electron Configuration for Alkaline Earth Metals


Electron configuration ends in s 2
2 valence electrons
1s 2s 2p
3p 4s
1s 2 2s 2 2p 6 3s 2 3p 6 4 s 2
3s

Electron Configuration for Halogens


Electron configuration ends in p 5
7 valence electrons
Example: Bromine
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4 p 5

Electron Configuration for Noble Gases

Except for Helium, they all end in p 6

Helium ends in s 2 (it only has 2 electrons)

Atoms are especially stable when the s and p sublevels are full (8 valence electrons)
Example: Argon
1s 2s 2p
1s 2 2s 2 2p 6 3 s 2 3 p 6
3s 3p
Outer level (3 rd level) has a total of 8 electrons

Orbital Diagrams and
Electron Configuration ws
13-40

Even if you don’t have the electron filling cheat sheet, there are two other ways to figure out the electron configuration:
•Create your own cheat sheet
•Use the layout of the periodic table

Create your own cheat sheet …
(1-7 spdf)
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s

Create your own cheat sheet …
Then fill from the bottom up following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
• 1s 2
= 2 electrons

Create your own cheat sheet …
Then fill from the bottom up following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
• 1s 2
2s
2
= 4 electrons
1s

Create your own cheat sheet …
Then fill from the bottom up following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
• 1s 2
2s
2
2p
6
3s
2
= 12 electrons

Create your own cheat sheet …
Then fill from the bottom up following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
• 1s 2
2s
2
2p
6
3s
2
3p
6
4s
2
= 20 electrons

Create your own cheat sheet …
Then fill from the bottom up following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
• 1s 2
2s
2
2p
6
3s
2
3p
6
4s
2
3d
10
5s
2
= 38 electrons
4p
6
Notice how the 4 th level begins filling before the 3rd is finished filling

Create your own cheat sheet …
Then fill from the bottom up following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
• 1s 2
2s
2
2p
6
3s
2
3p
6
4s
2
3d
10
4p
6
5s
2
4d
10
5p
6
6s
2
= 56 electrons

Use the periodic table layout

Use the periodic table layout

More Practice:
# e-
Na 11
Configuration
1s 2 2s 2 2p 6 3s 1
Cl 17 1s 2 2s 2 2p 6 3s 2 3p 5
Sb 51 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 3
K 19 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1

Noble Gas “Shortcut”
• The shape of the periodic table is a helpful clue
• When we get to the end of the period, the outermost energy level is full (noble gas)
• Write the symbol of the noble gas that comes before the element we are looking for [in brackets]
• Then write the rest of the electrons
Magnesium is 1s 2 2s 2 2p 6 3s 2
But Neon is 1s 2 2s 2 2p 6
Shortcut for Magnesium: [Ne]3s 2

Noble Gas “Shortcut”
Example 3
Write the symbol of the noble gas that comes before the element we are looking for
Then write the rest of the electrons
Chlorine is 1s 2 2s 2 2p 6 3s 2 3p 5
Neon is 1s 2 2s 2 2p 6
Shortcut for Chlorine: [Ne]3s 2 3p 5

Noble Gas “Shortcut”
Example 4
Write the symbol of the noble gas that comes before the element we are looking for
Then write the rest of the electrons
Potassium is 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1
Argon is 1s 2 2s 2 2p 6 3s 2 3p 6
Shortcut for Potassium: [Ar]4s 1

Noble Gas “Shortcut”
Example 5
Write the symbol of the noble gas that comes before the element we are looking for
Then write the rest of the electrons
• Ex: Argon:
1s 2 2s 2 2p 6 3s 2 3p 6
Argon is 1s 2 2s 2 2p 6 3s 2 3p 6
Shortcut for Argon: [Ar]
NO!
A noble gas cannot be its own shortcut!

51
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 3
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6
Kr
So, the shortcut is:
[Kr] 5s 2 4d 10 5p 3

Figure out the shortcut for
51
Sb using the table
Kr
Go backward until you hit a noble gas

Figure out the shortcut for
51
Sb using the table
[Kr] 5s 2 4d 10 5p 3

Figure out the shortcut for
51
Sb using the table
So, the shortcut for Sb is:
[Kr] 5s 2 4d 10 5p 3

Write the complete electron configuration and the noble gas shortcut electron configuration for
Polonium (Po)
Xenon (Xe)

Orbital Diagrams and
Electron Configuration ws