1. ELECTRON CONFIGURATION

2. The Bohr Model of the Atom Electron Orbits
In the Bohr Model, electrons travel in orbits around the nucleus
more like shells than planet orbits
The farther the electron is from the
nucleus the more energy it has.
n Energy level.

3. The Quantum-Mechanical Model Orbitals: (Erwin Schrödinger )
An orbital is a region where we have a very high probability of finding the electron when it has a particular amount of energy.
generally set at 90 or 95%

4. The electron cloud can be divided in:
Energy Sub-
levels
(s, p, d, f)
Atomic
Orbitals
(s, p, d, f)
Energy Levels
(1, 2, 3, 4….)

5. There is only one “s” Orbital (in each energy sub-level.
“s” Orbitals:
There is only one “s” Orbital
(in each energy sub-level.

6. “p” Orbitals
The p sublevel contains 3 orbitals, all with the same dumbbell-like shape

7. The d sublevel contains 5 orbitals.
“d” Orbitals:
The d sublevel contains 5 orbitals.

8. The f sublevel contains 7 orbitals.
“f” Orbitals
The f sublevel contains 7 orbitals.

9. Orbitals in each sublevel:
Shells & subshells:
Energy sublevels
Energy
levels
Orbitals in each sublevel: 1 3 5 7
Maximum # of electrons:

10. Pauli Exclusion Principle(A):
An atomic orbital may describe two electrons.
(No more than two electrons are admitted in each atomic orbital)
0ne “s” orbital ---
2 e- (maximum)
Three “p” orbitals ---
6 e- (maximum)
Five “d” orbitals ---
10 e- (maximum)
Seven “f” orbitals ---
14 e- (maximum)

11. Orbitals in each sublevel:
Shells & subshells:
Energy sublevels
Energy
level
Orbitals in each sublevel: 1 3 5 7
Maximum # of electrons: 2 6 10 14

12. Electrons enter the lowest energy level first.
Aufbau Principle:
Electrons enter the lowest energy level first.
1s 2s 2p 3s 3p 4s
1st Energy level
2nd Energy level
3srd Energy level
4th Energy level

13. 2p1 Z=5 1s 2s 2p 3s 3p 4s Example: 2 2 1 One electron 2nd Energy level
Sublevel
“p”

14. Examples: Na (Z=11) Mg (Z=12) Al (Z=13) Si (Z=14) Ne (Z=10)
1s2 2s2 2p6 3s2
3p1
1s2 2s2 2p6 3s2
3p2
1s2 2s2 2p6

15. Noble - gas notation:
Use the bracketed symbol of the nearest preceding noble gas in the Periodic Table, it will substitute the inner electrons.
Examples:

16. Na (Z=11) N (Z=7) Ca (Z=20) 1s2 2s2 3s2 4s2 Noble-Gas Notation: 3s1
[Ne]
3s1
1s2
2s2
2p6
3s1
[He]
2s2
2p3
1s2
2s2
2p3
1s2
2s2
2p6
3s2
3p6
4s2
[Ar]
4s2
It allows you to represent the complete electron configuration in a shorthand form.

17. Electron-Dots Structure:
The electrons in the outermost energy level are represented as dots around the element symbol:
valence electrons Al
[Ne] 3s2 3p1 Si
[Ne] 3s2 3p2 P
[Ne] 3s2 3p3

18. Electron – dots structure:
The element’s symbol represent the atom’s nucleus & inner levels electrons.
The dots represent the valence electrons (electrons in the outermost energy level).

19. Pauli Exclusion Principle (B):
The two electrons in each orbital have opposite spin.
Arrows are use to represent the electron and direction in an orbital diagram:
Orbital filling diagram:
2s p p p

20. When electrons occupy orbitals of equal energy, one electron enters each orbital until all of them contain one electron with parallel spin, then the second electron is added to each orbital so their pair the spin.
Hund’s Rule: 2 2 1 1 1
Z=7 1s 2s 2px 2py 2pz
Incorrect
Correct

21. Z=16 (16 electrons must be distributed) 1) Ground State Configuration:
Review:
Z=16 (16 electrons must be distributed)
1) Ground State Configuration:
2) Applying the Hund’s Rule:
(Two unpaired electrons)
3) Noble-Gas Notation:
4) Noble-Gas Notation & Hund’s Rule:
1s2
2s2
2p6
3s2
3p4
1s2 2s2 2p6 3s2
3px2
3py1
3pz1
[Ne]
3s2
3p4
[Ne]
3s2
3px2
3py 1
3pz1

22. 5) Orbital filling diagram: [Ne] 3s2 3p4
3s px 3py 3pz
6) Electron-Dot Structure: S
7) How many valence electrons it has? 6

23. P Practice: 1) Ground State Configuration: 2) Orbital filling diagram:
3) Applying the Hund’s Rule:
4) Noble-Gas Notation & Hund’s Rule:
5) Electron-dots:
Z = 15
1s2
2s2
2p6
3s2
3p3 3s
3px
3py
3pz
1s2 2s2 2p6 3s2
3px1
3py1
3pz1
[Ne]
3s2
3p3
[Ne]
3s2
3px1
3py1
3pz1 P
Valence e- : 5