Chemical Compounds and Bonding
Ionic Compounds
Ionic Compounds
• A compound is made up of two or more
atoms
• The force of attraction holding two atoms or
ions together is a chemical bond
• We can divide chemical compounds into two
types: ionic compounds and molecular
compounds
• Each type has distinctive properties
Properties of Ionic Compounds
• All composed of a metallic element and a
non-metallic element
– Ex: NaCl  salt
• These compounds share similar chemical
structures and exhibit similar properties
Properties of Ionic Compounds
• Ionic compounds have several properties in
common:
– Very hard and brittle
– High melting and boiling points
• Ex: NaCl melts at 801 ° C
– Conduct electricity as molten liquids BUT not as
solids
– Conduct electricity when dissolved in water
Properties of Ionic Compounds
• Pure water does not conduct electricity but if
we add table salt, NaCl, it dissolves easily to
make a salt solution that now conducts
electricity
• A substance that forms a solution that
conducts electricity is called an electrolyte
• Where have you seen electrolytes before?
– What do you think they do?
The Formation of Ionic Compounds
• We will look at the formation of NaCl
• Remember from previous classes that Na
wants to lose an electron to be stable (Na+)
and that Cl wants to gain an electron to
become stable (Cl-)
• An ionic bond forms when a non-metal atom
(Cl) removes an electron from the metal atom
(Na)
The Formation of Ionic Compounds
Na + Cl  [Na]+[Cl]Na wants to lose its outer electron and Cl wants to gain
one. Therefore, they both achieve their stable octet.
Si.nce Na is now positively charged and Cl is negatively
charged, there is an electrostatic force that keeps them
together. More specifically, it is an ionic bond.
Another Example
Mg + 2 Cl  [Cl]-[Mg]2+[Cl]Here, the 2 Mg electrons are taken up by two
different Cl atoms, making the ionic compound
MgCl2.
The Structure of Ionic Compounds
• When sodium chloride forms, large numbers
of the ions arrange themselves into crystals
• This arrangement is called a crystal lattice
structure
• The smallest repeating unit in an
ionic crystal structure as the formula
unit
• An ionic compound is not made up
of one positive and one negative ion,
it is made of huge numbers of the
ions is a fixed ratio
Explaining the Properties of Ionic
Compounds
• Ionic compounds have high melting points
because their ions are held together by strong
ionic bonds
• Ionic compounds are hard because their
bonds resist being ‘stretched’
• Ionic compounds are easily cracked or
fractured because an outside force will offset
the crystal lattice; suddenly finding positively
charged ions beside each other, quickly forcing
them apart
Explaining the Properties of Ionic
Compounds
• Ionic compounds are electrolytes because,
when placed in water, water molecules
surround each ion and separate it from the
crystal
– The ions are unable to move, and thus carry an
electric charge, through the water
Classwork/Homework
Page 60 #’s: 1-4, 7, 8