Transcript Ionic Bonding

Ionic Bonding
Lesson 4
August 30th, 2010
Ionic Bonding
• Ionic compounds are formed when one or
more valence electrons are transferred from
a metal atom to a non-metal atom.
• Usually a metal cation and an non-metal
anion.
• The charge of each ion correlates to the
number of electrons lost or gained.
• The two oppositely charged ions are
attracted to each other by a force called a
ionic bond.
Ionic Bonding
• The smallest amount of substance that has
the composition given by its chemical
formula is the formula unit.
• Ex. NaCl is a 1:1 ratio, MgCl2 is a 1:2 ratio.
Ionic properties / structure
• Ionic compounds are solids at SATP. In
their solid form they form solid ionic
crystals. These are more commonly known
as salts
General properties
• high MP, BP and hard. It takes a lot of
energy to break the bonds between the ions.
• Many are brittle
• When ionic compounds are dissolved in
water they dissociate into their ions.
• Conduct electricity when dissolved in water
• NaCl(s)  Na+(aq) + Cl-(aq)
how an ionic bond forms:
• Example+
Li
F
Li
F
how an ionic bond forms:
• Example 2
Na
Na
O
Na
O
Na
The Cross over rule
• This rule allows you to figure out how
many atoms you will need of each element
for bonding to occur without the need to
draw Bohr diagrams
Cross Over Rule
• Step 1.
•
Write the symbols, with the metal first (the
element with the positive charge)
•
Mg
I
• Step 2.
•
Write the Ionic charge above each symbol to
indicate the stable ion that each element forms.
2+
1Mg
I
Cross Over Rule
• Step 3. Draw an arrow from the metals
charge to the non-metal and an arrow from
the non-metal charge to the metal. (Cross
over the arrows)
2+
Mg
1I
Cross Over Rule
• Step 4. Fill in the number of atoms from each
element will have by following the arrows. If
need be reduce to lowest terms (in other
words, if they are the same number, you don’t
write those numbers down because you could
divide the whole molecule by that number
which would = 1)
MgI2
• (if the number crossed is a 1, the 1 is not
shown)
Example 2
• Step 1
•
Ca
O
Step 2
•
2+
•
Ca
2O
Example 2
Step 3
•
2+
•
Ca
2O
Step 4
•
Ca2O2 = CaO
• The 2’s disappeared because we reduced to
lowest terms.