Chemical Bonds
• A bond that forms because the nucleus (+) of
one atom is attracted to the electrons (-) of
another atom.
• Octet Rule: atoms tend to gain, lose or share
electrons so as to have 8 electrons
– Exception: Hydrogen only wants 2 electrons
Octet Rule
H
H
3s ___
2p___ ___ ___
2s ___
1s ___
3s ___
2p___ ___ ___
2s ___
1s ___
Octet Rule
H
Cl
3p___ ___ ___
3s ___
2p___ ___ ___
2s ___
1s ___
3p___ ___ ___
3s ___
2p___ ___ ___
2s ___
1s ___
Octet Rule
F
3p___ ___ ___
3s ___
2p___ ___ ___
2s ___
1s ___
F
3p___ ___ ___
3s ___
2p___ ___ ___
2s ___
1s ___
Chemical Bonds
Two Types:
• Covalent Bonding
– forms molecules
– sharing e– Polar & Nonpolar
• Ionic Bonding
– forms ionic compounds
– transfer of e-
Covalent Bonds
• Atoms are held together by sharing electrons
between nonmetals.
• Must fulfill the Octet Rule
• Bond Length- the average distance between
two bonded atoms
Diatomic Molecules
• A bond that has 2 atoms of the same element
• 7 diatomic molecules
– N2, O2, F2, Cl2, Br2, I2, H2
Single Covalent Bond
• Has 1 shared pair of electrons (2 e-)
Electron Dot Stuctures
• Shared Pair = valence electrons that are
shared by two atoms
• Unshared Pair = valence electrons that are not
shared by two atoms
Lewis Dot Structure
• Replace shared electrons with a dash
Practice Lewis Dot Structures
Chemical
Formula
# of Valence
Electrons
# of Bonded
Electrons
# of
Remaining
Electrons
Lewis Dot
Structure
F2
7 x 2= 14
2
12
F—F
H2O
NH3
CH4
Octet Check
All Atoms=8
Hydrogen=2
Double Covalent Bond
• Has 2 shared pairs of electrons (4 e-)
Triple Covalent Bond
• Has 3 shared pairs of electrons (6 e-)
Practice Lewis Dot Structure
Chemical
Formula
O2
CO2
N2
HCN
# of Valence
Electrons
Single Line
Bond
Structure
# of
Remaining
Electrons
Lewis Dot
Structure
Octet Check
All Atoms=8
Hydrogen=2
Polar Covalent
•An unequal sharing of electrons between two
atoms
• HCl
•One atom has a slightly negative (-) charge, and
the other atom has a slightly positive (+) charge
Dipole
• A polar covalent bond creates a dipole.
• A dipole has “two poles” with opposite
charges.
• Represented by an arrow pointing toward the
negative end
Practice Drawing Dipoles
P- Br
P = 2.1
Br = 2.8
H- Cl
H= 2.1
Cl= 3.0
P –Br
+
-
H – Cl
+
-
Nonpolar Covalent Bonds
• A Nonpolar Covalent Bond is equal sharing of
electrons between two atoms
• Cl2, N2, O2
Classwork
1.
2.
3.
4.
Define the octet rule.
Define a covalent bond.
Define an ionic bond.
Draw the Lewis Structure of:
a. IBr
b. C2HCl
Ionic Bond
• Electrons are transferred between two atoms
with very different electronegativity
• Always formed between metals and nonmetals
+
[METALS ]
• Produce charged ions
[NON-METALS ]
Ionic Bonds
Na
+
Na+ +
Cl
Na
3p___ ___ ___
3s ___
2p___ ___ ___
2s ___
1s ___
Cl
3p___ ___ ___
3s ___
2p___ ___ ___
2s ___
1s ___
Cl
-
Ionic Bonds
• Ca
+ F + F
Ca2+ + F
-+
F
-
Ionic versus Covalent
IONIC
COVALENT
Bonded Name
Salt
Molecule
Bonding Type
Transfer e-
Share e-
Types of Elements
Metal & Nonmetal
Nonmetals
Physical State
Solid
Solid, Liquid, or Gas
Melting Point
High (above 300ºC)
Low (below 300 ºC)
Solubility
Dissolves in Water
Varies
Conductivity
Good
Poor
Types of Bonds
• Type of bond = Electronegativity AElectronegativity B
Type of Bond
Nonpolar Covalent
Electronegativity
Difference
0  0.3
Polar Covalent
0.4  1.7
Ionic
1.8  3.3
Practice
•
•
•
•
N—H
Ca—Cl
Al—Cl
H—F
N=3.0 ; H=2.1
Ca=1.0 ; Cl=3.0
Al=1.5 ; Cl=3.0
H=2.1 ; F=4.0
Practice
1. What type of bond is HCl? (H = 2.1, Cl = 3.1)
2. What type of bond is H2? (H=2.1)
3. What type of bond is MgO? (Mg=1.2, O=3.5)
Attractions Between Molecules
Besides ionic, metallic, and covalent bonds,
there are also attractions between
molecules attractions are weaker than
Intermolecular
ionic, covalent, and metallic bonds
There are 2 main types of attractions between
molecules: Van der Waals and Hydrogen
Van der Waals Forces
• Van der Waals forces consists of the two
weak attractions between molecules
1. dipole
interactions –
polar molecules
attracted to one
another
2. dispersion
forces –
caused by
the motion
of electrons
(weakest of
all forces)
Hydrogen Bond

Hydrogen Bonds are forces where a
hydrogen atom is weakly attracted to an
unshared electron pair of another atom
Hydrogen Bond

This other atom may be in the same
molecule or in a nearby molecule, but
always has to include hydrogen
Hydrogen Bonds have about 5% of the
strength of an average covalent bond
 Hydrogen Bond is the strongest of all
intermolecular forces

Intermolecular Attractions

A few solids that consist of molecules do
not melt until the temperature reaches
1000ºC or higher called network solids
(Example: diamond, silicon carbide)

A Network Solid contains atoms that are
all covalently bonded to each other
• Melting a network solid would require breaking
bonds throughout the solid (which is difficult to do)