IONIC BONDING PART 2
IONIC BONDING
• IONIC BONDING occurs between two
IONS with OPPOSITE CHARGES.
• Remember OPPOSITES ATTRACT!
Characteristics of IONIC Compounds
• Generally consist of a METAL CATION
and a NON-METAL ANION.
• High melting points
• Almost always solid at room temperature
• Brittle
• Generally not very flammable
• Dissolve in water [electrolytes]
Forming an IONIC Compound
• What would be the formula for a
compound resulting from ionic bonding
between Potassium and Bromine?
• STEPS
• 1. Find the elements in the Periodic
Table and write their symbols.
• 2. Use the element’s location on the
Periodic Table to predict the charge of
its ION.
• Write the symbols and charges in this
manner:
[ +1 ] + [ -1 ]
K
Br
• When forming an IONIC COMPOUND, the
OVERALL CHARGE of all the ions must
add up to equal ZERO!
[ +1 ] + [ -1 ] = 0
K
Br
• Sometimes, the charge will add to zero with
no more work needed, as in the case of
POTASSIUM and BROMINE.
[ +1 ] +
K
[ -1 ] = 0
Br
• If this occurs, this means the FORMULA of the
compound needs ONE ATOM OF EACH
ELEMENT.
• When writing the formula, the POSITIVE ION
goes FIRST, the NEGATIVE SECOND.
• So the formula for a compound of
Potassium and Bromine is:
•
KBr
What happens if the charges do not
add up to be ZERO?
• If the charges do not add to zero, them we
must make them do so.
• PROBLEM
• What is the formula for an ionic compound
of Magnesium and Chlorine?
• Determine the symbol and charge of both
elements:
•[+2 ] + [-1 ] = 0
•Mg
Cl
• If the two charges DO NOT ADD TO
ZERO:
• Cross-multiply the charges of the ions,
IGNORING THE SIGN [all positive].
•
•
•
1 [+2 ]
Mg
+ 2 [-1 ] = 0
Cl
The number used to multiply the ion’s
charge by is used when writing the
FORMULA for the compound and is called
a SUBSCRIPT. A SUBSCRIPT tells us
HOW MANY ATOMS of the element are
needed in the compound’s FOMULA
UNIT.
Thus, the formula of the compound is:
MgCl2
Problem
What is the formula of an ionic compound of
Aluminum and Oxygen?
•[ +3] + [ -2 ] = 0
•
Al
O
•[ +3] +
•
Al
[ -2 ] = 0
O
•2 [ +3] + 3 [ -2 ] = 0
•
Al
O
• So the formula becomes:
• Al2O3