1. Lewis Structures, Orbital Diagrams, & Electron Configuration
Chiquita McDaniel
General Chemistry I Laboratory

2. How to Draw Lewis Structures
Two types: Covalent (sharing e-s) & Ionic (transfer e-s)
COVALENT
Draw the skeletal structure
Least electronegative element as the central atom
F and H always occur as outer atoms
Count the number of valence electrons present
Draw bonds in between the outer atoms and the central atom (each bond has two electrons)
Complete the octet of the outer atoms (8 e-s)
There are three exceptions to this rule (read pages in your book)
Then complete the octet of the central atom if there are e-s present, if not take e-s from outer atoms to make a double or triple bond

3. Example
CO2
NH3
NH4+

4. IONIC COMPOUNDS
Take each atom and draw the valence e-s surrounding the atom
Show how the e-s are transferred from each atom
Draw brackets around each individual atom, placing the transferred electrons on the atom
Example: K2O , NaCl

5. Resonance
When more than one Lewis structure exists for a compound
Caused by delocalized bonding (double bonds)
These double bonds can be at either bond at any given time
However only one is more plausible than others
Determined by calculating formal charges
Example O3

6. Calculating Formal Charges
FC= total number of valence e-s – (# of non bonded e- s + 1/2 of the # of bonded electrons)
Choosing the correct Resonance structure
Sum of all formal charges in a neutral molecule must be zero
Sum of all formal charges in an ion must equal to the charge of the ion
Small or zero formal charges on individual atoms are better than large ones
Negative charges should reside on the most electronegative atom
Adjacent negative formal charges should be avoided

7. Orbital Diagram & Electron Configuration

8. ELECTRON CONFIGURATION
s, p, d, f
Types of sublevels, each have a specific number of orbitals
S: 1 orbital holds only 2 e-s
P: 3 orbitals holds only 6 e-s
D: 5 orbitals holds only 10 e-s
F: 7 orbitals holds only 14 e-s
Orbitals fill in the following order
1s2s2p3s3p4s3d4p5s4d5p6s
This is called the ground state configuration using the “Aufbau” principle (build up)
The number represent the energy level its on (period) and the letter represents which orbital the electron resides in
Can use the periodic table to predict the order of filling without remembering the order above.

9. ELECTRON CONFIGURATION
Nobel gas configuration: is using the electron configuration of Nobel gas preceding the atom as the core and then adding on the remaining electrons.

10. Orbital diagram N O 1s 2s 2p 1s 2s 2p Expanded version of EC.
Shows the orientation of the individual electrons in their orbitals
Two Rules to Keep in Mind
Pauli Exclusion Rule
Orbitals can’t hold more than two electrons
No 2 electrons can have the same 4 Quantum Numbers
Hund’s Rule
Electrons occupy these orbitals singularly first then pair up
N O
1s 2s p s 2s p