1. Section 5.2 The Quantum Theory and the Atom
Honors Chemistry
Section 5.2
The Quantum Theory and the Atom

2. WHERE is the electron?
We now know the electrons are arranged in “shells” or “energy levels” around the nucleus.
…so how are they arranged in an atom?
Neils Bohr suggested the electrons were in “orbit”, like planets…

3. Bohr thought that when electrons absorbed energy they moved to one of his higher “orbits”.
Then, when they fell back to a lower “orbit”, these excited electrons gave off that energy as light waves.

4. …but if electrons “orbit” the nucleus they would lose energy constantly, and fall into the nucleus – but they don’t!…
So, exactly where are the electrons in an atom?

5. WHERE is the electron?
Heisenberg reached the conclusion that it is impossible to observe any object without disturbing it —at least a little.
The smaller the object, the greater the disturbance.
So What?

6. Observing an electron produces an unavoidable uncertainty about its location or motion!!
The Heisenberg uncertainty principle states we cannot know the motion and position of a particle at the same time.
We can know one, but not both!

7. The Electron Cloud Model
Every time we detect the electron, we change its speed and direction!
We can’t tell where the electron IS… (only where it WAS)…
(think of a lightning bug blinking around a bush…)
We can only predict a zone where the electron is most likely to be, the next time we look. (it’s all a matter of probability!)

8. The “Electron Cloud”
The “electron cloud” is a 3-D map of dots showing where the electron has been …
(There is NO “cloud of electrons”, just a cloud of DOTS showing where the electron is most likely to be!
nucleus
Note that there is no electron “path”!

9. The “Electron Cloud”
This three-dimensional region around the nucleus shows the electron’s probable location. This is called an atomic orbital. (NOT “orbit”!)
The dots are most dense where the electron is found most often.
nucleus

10. The “boundary” of an orbital defines the volume that contains the electrons 90% of the time.
10%
90%
(There is no actual “boundary”, because there is actually a tiny probability the electron may be anywhere!)

11. The principal quantum number, “n” (n = 1 to 7), tells what shell contains the orbital!
These numbers for “n” (1 – 7) describe the size (and energy) of the electron’s orbital.
As “n” increases from 1 to 7, the orbital is in a larger shell. The electron spends more time farther from the nucleus and has a higher energy.

12. An orbital with a higher “n” (principal energy level) is in a shell that is (on average) farther out from the nucleus, and has more energy!
5th energy level n=5
4th energy level n=4
3rd energy level n=3
2nd energy level n=2
1st energy level n=1

13. O.K., so far…
Electrons are located around the nucleus in shells, or “energy levels” according to their energy.
These “shells” are called “principal energy levels” (n), and are numbered (n = 1 is the first shell, etc)
The electrons actually exist in “orbitals” (a 3-dimensional space) within each shell.

14. A shell with a higher “principal quantum number” (n) is (on average) farther out from the nucleus.
“Outside” shells (higher “n”) have greater energy than “inside” shells.

15. How An Electron’s Energy Can Change
When electrons absorb energy, they can move farther away from the nucleus, into a higher energy level, or shell. (to a higher “n”)
They can also move into another orbital that has a more complex shape.

16. Orbitals with complex shapes have higher energy
Orbitals with complex shapes have higher energy. (A simple shape requires less energy).
Orbitals come in many shapes…
The shape of the orbital depends upon what kind of “subshell” the electrons are in!
SUBSHELL?!

17. YES! SUBSHELL! (or “sublevel”)
Electrons exist in “orbitals”.
Orbitals are found in subshells, which determine the orbital’s shape.
Subshells combine to make up shells, (or principal energy levels).
Shells combine to make the atom’s “electron cloud”.

18. Subshells
Each subshell type has its own energy, because each type has its own shape…
…and there are four kinds of subshells:
In order of increasing energy, they are called:
“s”
“p”
“d”
and
“f” subshells

19. How Many Subshells are in each Shell?
Energy level 1 (1st shell; n=1) has 1 subshell: s
Energy level 2 (2nd shell; n=2) has 2 subshells: s & p
Energy level 3 (3rd shell; n=3) has 3 subshells: s, p, and d
…and…
Energy level 4 (4th shell; n=4) has 4 subshells: s, p, d, and f
Larger shells have more volume (more space) to contain more subshells – more orbitals and more electrons.

20. Orbitals are in Subshells
Each type of subshell holds a different number of orbitals, but each orbital can only hold 2 electrons.
“s” subshells have only 1 orbital (max = 2 e-)
“p” subshells contain 3 orbitals (max = 6 e-)
“d” subshells contain 5 orbitals (max = 10 e-)
And “f” subshells contain 7 orbitals! (max = 14 e-)
All orbitals hold a MAXIMUM of 2 electrons!

21. Shell (E level) subshells orbitals electron capac.
1st Shell (n=1)
One “1s”
One “1s”
2 electrons
2nd Shell (n=2)
One “2s”
One “2s”
2 electrons
One “2p”
Three “2p”
6 electrons
3rd Shell (n=3)
One “3s”
One “3s”
2 electrons
One “3p”
Three “3p”
6 electrons
One “3d”
Five “3d”
10 electrons
4th Shell (n=4)
One “4s”
One “4s”
2 electrons
One “4p”
Three “4p”
6 electrons
One “4d”
Five “4d”
10 electrons
One “4f”
Seven “4f”
14 electrons

22. Shells, Subshells, and Orbitals
For example, the third shell (n=3) has 3 subshells, each with its own orbitals:
All in the 3rd shell! (9 total orbitals)
3d subshell contains five 3d orbitals
3p subshell contains three 3p orbitals
3s subshell contains one 3s orbital
So the 3rd shell (E level) can hold as many as 18 electrons (2 electrons per orbital)

23. The “s” orbital
Every shell has an “s” subshell – a sphere.
Every “s” subshell has only ONE orbital!
The 1s orbital For every atom there is a single “1s” orbital. The "1" in 1s means the orbital is in the 1st energy level. The "s" indicates the shape of the orbital. (All s orbitals are spheres surrounding the nucleus).

24. “2” = 2nd shell! The “p” orbitals
All shells above #1 contains a “p” subshell.
(The first shell with a “p” subshell is the 2nd shell).
Each “p” subshell has three “p” orbitals (x, y, & z)
(These 3 orbitals are called “2px”, “2py”, & “2pz”)
“2” = 2nd shell!
Each “p” orbital can hold up to 2 electrons.
Therefore, a “p” subshell can contain up to:
6 electrons!

25. O.K. - So Far… This is a 1s orbital! (capacity = 2 e-)
This is a 2s orbital! (2 e-)
It’s bigger! (farther out)
This is a 2p orbital! (2 e-)
More complex shape, so more energy!
This is the 2p subshell! There are three p orbitals for a total of 6 e-.

26. The Electron Cloud…Through Two Energy Levels!
Total = (10 electrons)
The nucleus
1s orbital
2s orbital
2px orbital
2py orbital
2pz orbital

27. Electrons per shell…
Since the first shell has a single “s” subshell (1s) with…
…ONE “s” orbital (called the 1s orbital),
the first shell can hold:
Just 2 electrons!
Since the second shell has an “s” AND a “p” subshell (2s, 2p):
…it contains one “2s” orbital and three “2p” orbitals.
This means the 2nd shell has four orbitals and can hold:
8 electrons!

28. The “d” orbitals
Every shell above #2 contains a “d” subshell.
Each “d” subshell has five “d” orbitals!
Note how complex the d orbitals are! (higher energy than p orbitals)
The 3rd shell is the first shell with a “d” subshell!
Each “d” orbital can hold up to 2 electrons.
Therefore, a “d” subshell can contain up to:
10 electrons!

29. The “f ” orbitals
Every shell above #3 contains a “f” subshell.
Each “f” subshell has seven “f” orbitals!
The f orbitals are even more complex (higher energy) than d orbitals!
The 4th shell is the first shell with a “f” subshell!
Each “f” orbital can hold up to 2 electrons.
Therefore, a “f” subshell can contain up to:
14 electrons!

30. The Quantum Theory (simplified)
Each electron has 4 quantum numbers to describe it…
1. The “principal quantum number” (n) = the shell number
2. The “angular momentum quantum #” (l )= the subshell type
3. The “magnetic quantum number” (ml) = which orbital
4. The “spin quantum number” (ms) = the spin (  or  ) of the electron
EVERY ELECTRON IN AN ATOM IS UNIQUE, WITH ITS OWN SET OF FOUR QUANTUM NUMBERS!