1. IONIC BONDING PART 2

2. IONIC BONDING
IONIC BONDING occurs between two IONS with OPPOSITE CHARGES.
Remember OPPOSITES ATTRACT!

3. 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]

4. 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.

5. Write the symbols and charges in this manner:
[ +1 ] [ -1 ]
K Br

6. When forming an IONIC COMPOUND, the OVERALL CHARGE of all the ions must add up to equal ZERO!
[ +1 ] [ -1 ] = 0
K Br

7. Sometimes, the charge will add to zero with no more work needed, as in the case of POTASSIUM and BROMINE.
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.
[ +1 ] [ -1 ] = 0
K Br

8. So the formula for a compound of Potassium and Bromine is:
KBr

9. 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?

10. Determine the symbol and charge of both elements:
[+2 ] [-1 ] = 0
Mg Cl

11. If the two charges DO NOT ADD TO ZERO:
Cross-multiply the charges of the ions, IGNORING THE SIGN [all positive].

12. 1 [+2 ] [-1 ] = 0
Mg Cl

13. 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

14. Problem
What is the formula of an ionic compound of Aluminum and Oxygen?
[ +3] + [ -2 ] = 0
Al O

15. [ +3] [ -2 ] = 0
Al O

16. 2 [ +3] [ -2 ] = 0
Al O

17. So the formula becomes:
Al2O3