Introduction to Chemical
Bonding
Bond Formation
Ionic Bonds
Covalent Bonds
Chemical Bonds
• An attractive force that holds atoms together
• Formation of chemical bonds involves energy
– Bonds will form if atoms have lower energy than
when they are separated
– Bond formation is (generally) an exothermic
process
• Bonding deals with valence electrons
– Electrons in the highest energy level
Lewis Structures
• Symbolic representations of elements that
show the valence electrons
• Elemental symbol and the valence electrons
represented by dots
Valence Electrons & Noble Gases
• Noble gases are unreactive
– They don’t form compounds with other elements
• Noble Gases already have a stable electron
configuration
• The highest energy level of the atom is full
and it will not form any bonds
– Does this always mean there are eight electrons?
– No → Helium
Valance Electrons and Chemical
Properties
• The number of valence electrons determines
the chemical properties of an atom
• Atoms are trying to get to eight valance
electrons and they will take the shortest route
to get there
– “Octet Rule”
– Could mean gaining electrons, could mean loosing
electrons
– “1,2,3,4,5,6,7,8,1,2,3,4…”
Ion Formation and the Octet Rule
• Octet Rule
• Atoms will gain or lose electrons to have a full
outer shell (valence shell)
– Metals lose valence electrons so that the electron
configuration becomes like the previous noble gas
– Non-metals gain electrons to become like the next
noble gas
• Exceptions exist for small atoms
– Duet Rule
How does the bond between sodium &
chlorine form?



Cl


Sodium has
one valence
electron. It’s
looking to lose
it
Na
Chlorine has seven
valence electrons.
It’s looking to gain
one
Ion Formation and the Octet Rule
• Main group metals lose all their valence
electrons to form cations
– This loss of electrons is called oxidation
• Non-metals gain electrons to achieve the
noble gas configuration and form anions
– This gain of electrons is called reduction
• “OiL RiG”
– Oxidation is loss, Reduction is gain
How does the bond between sodium &
chlorine form?

Na
 
Cl


Sodium
now has 11
protons &
10
electrons.
It has a
positive
charge. It
is a cation
Chlorine
now has 17
protons &
18
electrons.
It has a
negative
charge. It
is an anion
Ionic Bond
• Negative charges are attracted to positive
charges
• Negative anions are attracted to positive
cations
• The result is an ionic bond
– Ionic Bonds involve the transfer of electrons from
a metal to a non-metal
How does the bond between sodium &
chlorine form?


Na
 
Cl

The negative charge on the chloride ion
and the positive charge on sodium ion
attract each other and form an ionic
bond
Structure of an Ionic Solid
• Ionic Compounds form
a three-dimensional
network called a crystal
(or crystal lattice)
• Each ion is attracted to
multiple ions of the
opposite charge
Properties of Ionic Compounds
• High melting point
– Don’t easily change to liquids (or gases)
• Solids → Poor conductors
• Liquids → Good Conductors
• Shatters when breaks