2. 2.4- Quantum Mechanical Model

3. Quantum Numbers 2px↑ Principle Angular momentum Magnetic Spin
Each electron must have a different location (atomic orbital) in the atom
The electrons are described by four quantum numbers.
Principle
Angular momentum
Magnetic
Spin
2px↑

4. Principle Quantum Number
Energy Level where the electron is located
Numbered 1 to 7 out from the Nucleus
level 1 holds 2 electrons
level 2 holds 8 electrons
level 3 holds 18 electrons
level 4 holds 32 electrons
These energy levels correspond to the periods on the periodic table

5. Angular Momentum Quantum Number
Shape of the atomic orbital
The shapes are s, p, d, f (you must know these!)
s are spherical
p are dumbbell
d are double- dumbbell
f are quadruple-dumbbell
Shape
Suborbitals s 1 p 3 d 5 f 7
Energy Level
Shapes 1 s 2
s,p 3
s,p,d
4-7
s,p,d,f

7. Spin Quantum Number Each atomic suborbital can hold 2 electrons
Electrons spin like a top
Pauli Exclusion Principle
No 2 electrons can have the same set of four quantum numbers
2 electrons paired in the same orbital must spin in opposite directions
If one is clockwise the other is counterclockwise
Spin is shown as ↑ or ↓

8. Aufbau Principle Electrons occupy the orbitals of lowest energy first
Note: orbitals with the same energy level and shape have the same energy regardless of orientation
The Periodic Table is a guide for the Aufbau Principle, going from left to right as you move down the periodic table
Each element represents one electron

9. Orbital Diagrams
Each atomic suborbital has a box (2 electrons per box)
Hund’s Rule: Give each orbital (of equal energy) one electron before any get two electrons

10. Sample Problems O Fe N He Example: Be 1s2, 2s2 [He], 2s2
Write the electron configuration, the shorthand and draw the orbital diagram for the following elements: O Fe N He
Example: Be
1s2, 2s2
[He], 2s2

11. Lewis Structures • • • N • • Bohr model • • • • N • • •
Place only valence electrons around the element symbol • N • •
Bohr model • • • •
draw all electrons in the appropriate levels N • • •