Lewis Structures
Electronegativity and Bond Types
-
Find the difference in electronegativities of the two elements involved
0.5
1.67
Pure
Covalent
Polar
Covalent
Ionic
Pure Covalent – share electrons evenly, non polar, made up of 2 nonmetals and/or metalloids
Polar Covalent – share electrons unevenly, one element holds electrons more than the other
--polar, made up of 2 nonmetals, and/or metalloids
Ionic – transfer of electrons, made up of a 1 metal and 1 non-metal
Electronegativity – the relative tendency of an atom to attract electrons.
Ex:
Al = 1.5
O = 3.5

Al2O3 = 2.0 = ionic
Al = 1.5
N = 3.0

AlN = 1.5 = polar covalent
Big difference = ionic
Slight difference = polar covalent
Small difference = pure covalent
Bond Strength and Type
What type of bond does NaCl have?
Na (1.01)
and
Cl (2.83)
They create a strong ionic bond.
difference of 
1.82
What type of bond is H2O?
H (2.1)
and
O (3.5)
They create a polar covalent bond.
difference of 
1.4
What type of bond is N2?
N is 3.0 and you have 2 of them, 3.0 – 3.0 = 0
It creates a pure covalent bond with itself.
Lewis Dot Diagrams
H2 H H bond to form H H
-
or H – H
Each bond uses an electron from each atom.
To create a Lewis Dot Diagram:
1) Count the total # of valence electrons available.
a. Account for ALL valence electrons
2) Ensure EACH atom has an octet, or a pair for H (2 electrons total)
a. We want each element to have 8 valence electrons for itself
The Lewis Dot Diagram for CH4 is:
Valence electrons:
H has 1 and we have 4 H’s  so 4 valence electrons
C has 4 valence electrons
Total valence electrons = 8
C
H
H
H
H
So, the Lewis Dot Diagram would be:
H
H C H
H
** a – dash is equal to 2 ‘s
OR
( ) or an electron pair**
H
H–C–H
H