Unit 11: Chemical Bonding
Section 1: Ionic and Covalent
Bonding
Chemical Bonds
• Forces that hold atoms or ions together
to make all molecules and compounds
• There are two main type of bonds
– Ionic bonds and covalent bonds
Ionic Bonds
• Bonds achieved by transferring valence
electrons
– Due to a positive (metal) and negative
(nonmetal) attraction
The Lewis Symbol
• In ionic bonding, atoms gain and lose electrons
to achieve a noble gas electron configuration (a
stable state)
• Lewis symbols use dots to represent an
element’s number of valence electrons
– Na has 1 valence electron

Na
– Cl has 7 valence electrons

Cl
– The order for applying dots is right, left, top,
bottom, right, left, top, and bottom
• The maximum dots possible is 8, and the least dots possible
is 1
Using the Lewis Symbol for Ionic Bonds
• sodium and chlorine  NaCl
– Na
Cl
• magnesium and chlorine  MgCl2
– Mg
Cl
Cl
• The 1st element needs to get rid of its valence
electrons, and the 2nd element needs to gain a
total of eight valence electrons in order to be
complete
Covalent Bonds
• Bonds achieved by sharing valence electrons
– A bond between two nonmetals (two negatively
charged atoms)
• There are two types of covalent bonds:
nonpolar covalent and polar covalent
– Nonpolar covalent bonds have equally shared
valence electrons, where the attraction is even
throughout
– Polar covalent bonds have unequally shared
valence electron, where the attraction is being
pulled more toward the atom with the higher
electronegativity
Determining Polarity
• If the electronegativity difference falls
between 0.0 to 0.2, the bond is nonpolar
covalent
• If the electronegativity difference falls
between 0.3 to 1.4, the bond is polar
covalent
• If the electronegativity difference is
1.5 or greater, the bond is ionic
Determining Polarity
• Determine the polarity of MgCl2
• Mg = 1.2 and Cl = 3.0, so 3.0 – 1.2 = 1.8  IONIC
Using the Lewis Symbol for
Covalent Bonds
• Lewis structure for SiH4
H
H
Si
H
H

H
H Si H
H
• The goal is to get all the unpaired valence
electrons to bond together