SCH3U Chemical
Bonding
Ionic vs. Covalent Compounds
Ms. Manning
Formation of Bonds
Chemical Bonds are formed between two atoms
using shared valence electrons; this is the force
that holds atoms together in compounds.
Valence Electrons are the electrons that
occupies the outermost energy level of an atom
Type of Bonds
Ionic vs. Covalent
 Ionic bonding occurs between metals and non-metals
 Covalent bonding occurs between non-metals
Note: Bonding between metals is called Metallic bonding

Video Clip: Chemical Bonding
Bonding Animation
Octet Rule
Most Noble gases have 8 electrons in their outer shell.
This is a stable conformation. Thus, the noble gases do
not react with other elements. In other words, noble
gases are very stable.
Octet Rule (Continued)
When atoms form ions or combine in compounds
they obtain electron configurations of the nearest
noble gas (eight electrons in their valence shells)
Ionic Bonding
Ionic Bonds are formed from the electrostatic
attraction of positive and negative ions
An atom that can
lose an electron to
become a positively
charged ion, called
a cation
An atom can gain
electrons to become
a negatively charged
ion, called an anion
•In each case, the atom attains a noble gas configuration with
its valence electrons.
•A noble gas configuration is defined as a completely filled
outer shell, like the noble gases.
Ionic Bond: Example (Na and Cl)
Ionic Bond:
Example
(Al and O)
Al
O
O
Al
O
Covalent Bonding
Covalent bonding occurs between two non-metals. Covalent bonding is
different from ionic bonding because electrons are shared instead of
transferred.
Each atom has eight shared electrons
Covalent Bonding: Example (H
and F)
H
F
HF
Electronegativity and Polarity
Nonpolar Covalent Bond


When electrons are shared between 2
atoms, a covalent bond is formed.
If the atoms are identical, e.g. Cl2, the
electrons are shared equally (nonpolar)
Polar Covalent Bond


If the electrons are shared between 2 different
atoms, e.g. HBr, the sharing is unequal
The bonding electrons spend more time near the
more electronegative atom
H
Br
(Continued)

This is not a complete transfer of an electron from hydrogen to
fluorine; it is merely a drifting of electrons toward fluorine
H F Cl Cl
:
Polar Covalent

:
Covalent
When a charge separation of this type is present, the molecule
possesses an electric dipole, so called “dipole moment” and the
bond is called a POLAR COVALENT BOND
(Continued)
-
O
Example: Water (H2O)
∆EN = 1.24 (which is between 0.5 and 1.7)
H
H
Polar Covalent Bond
+
+
Oxygen = a slightly negative charge
Hydrogen = a slightly positive charge
Since the hydrogen does not completely transfer its
electron to the oxygen, the their respective charges
are indicated as  + (the indication of partial positive
charge) and  - (indication of partial Negative
charge).

Electronegativity Differences


The absolute value of the difference in
electronegativities of two bonded atoms
provides a measure of polarity of a bond.
The greater the difference, the more polar the
bond.
0 to 0.4
0.41 to 1.69
> 1.7
Nonpolar covalent
Polar covalent
Ionic
Electronegativity Difference
Comparison of Ionic, Nonpolar covalent and Polar
covalent bonding
3.3
1.7
[Na]+[Cl]-
0.5
H+ - Cl-
0
Cl - Cl
∆EN
Summary
Chemical Bonds are formed between the atoms in
molecules
The bonds are formed from the valence electrons of the
atoms and the resulting bond allows each atom to achieve a
noble gas configuration (the most stable arrangement of
electrons around the atom: Octet Rule)
The types of bonding can be classified as:



1.
2.
3.
Covalent (non-metal bondin; 0<∆EN<0.5)
Polar covalent bonds (non-metal bonding with a dipole
moment; 0.5<∆EN<1.7)
Ionic (metals + non-metals; 1.7 <∆EN< 3.3)
Questions

Complete the chart:

Identify each compounds as ionic or covalent: CCl4,HCI, MgF2,
H2O,NH3, NaCl, OH, H2
Show how the bond forms between Li+Cl, Mg +O (Follow the Octet
Rule) as well as Li + O

Polar Molecules

Note: Not all molecules with polar bonds are
polar molecules
Polarity
The overall polarity of a molecule depends on
a combination of:
the polarity of the bonds
the shape of the molecule
Polarity of Molecules
To predict the polarity of the molecule:
i.
Determine if there are polar bonds using
EN value
ii. If there are polar bonds, establish the
direction of the dipoles.
(A dipole exists when two opposite
charges are separated by a short
distance)
( +   -)
Polarity of Molecules
iii. Once you identify the shape of the molecule


if the dipoles cancel due to the shape of the
molecule then the compound is non-polar
if the dipoles do not cancel due to the shape of
the molecule then the compound is polar
Polarity of Molecules-Examples
Chemical
formula
CH4
methane
CO2
H2O
Lewis
diagram
Stick
diagram
Shape
Polarity
of
molecule
(polar/
non-polar)
Shapes of Molecules
To illustrate the shape of the molecule using a Lewis
diagram:
i. Determine the “central atom” , i.e. the atom
requiring the most electrons.
ii. Determine how many electrons each atom needs to
gain in order to become isoelectronic with its closest
noble gas.
iii. Determine if multiple bonds are needed.
iv. Determine the structural shape of the molecule based
on
 # atoms bonded to central atom
 # lone pairs of electrons
 (see handout of molecular shapes)
Shapes of Molecules-Examples
Chemical
formula
CH4
methane
CO2
H2O
Lewis
diagram
Stick
diagram
Shape