Ionic Bonds and Properties of
Ionic Compounds
Ions
 Recall that atoms lose or gain electrons to form ions.
 Metals tend to lose electrons and form positively
charged ions called cations.
 Nonmetals tend to gain electrons and form negatively
charged particles called anions.
 They do this to acquire a stable octet (full outer
energy level – usually 8 valence electrons).
 For the representative elements (groups 1,2 &1-17) we
can tell the charge of the ion by the number of
valence electrons. Remember: 1+, 2+, 3+, skip, 3-, 2-, 1-,
zip!
Ionic Compounds
 Because opposites attract, cations and anions are
attracted to each other and form neutral compounds
often referred to as salts.
 Since the positive and negative charges have to zero
out, the formula for an ionic compound will give the
ratio of each element.
 Individual particles of an ionic compound are called
formula units, but they do not exist in isolation. They
form a repeating crystalline structure called a crystal
lattice.
Properties of Ionic Compounds
Let’s fill in the chart!!
 Think about it for a minute – what ionic compound
are you very familiar with? Table salt – sodium
chloride. You worked in lab with several other salts.
What state of matter were they all at room
temperature?
 If you said solids you are correct!! Now think about
why that might be.
 It is because of the strong attractive forces among
the ions and formula units
Melting & Boiling Points
 Have you ever tried to melt table salt? If so it probably
didn’t work very well. Why?
 Melting and boiling points of ionic compounds are
relatively high. Why?
 Those strong bonds that make them solids at room
temperature also require lots of energy to break thus
resulting in high melting and boiling points.
Solubility
 Generally when we talk about solubility, we are
referring to solubility in water.
 Ionic compounds are usually soluble in water. Why?
 Water molecules are polar (we’ll talk more about that
later) and will pull the ions apart.
Response to Stress or Deformation
 What does that mean???
 Basically it means if you hit it with a hammer, what
happens???
 Yep, it crumbles – that’s because ionic compounds
tend to be brittle. Why?
 In the crystal lattice, ions have to be lined up with
opposite charges and if that gets shifted, then like
charges repel - it breaks!!
Conductivity
 As solids, ionic compounds are not good conductors
of electricity.
 However, when dissolved in water or in a molten
state they are good conductors. Why?
 In order to move electrons (that’s what an electrical
current is) you need charged particles – in this case
ions- for them to move through. Within the crystal
lattice, there are no loose charged particles for
transferring the electrons!!