1. Ionic Compounds

2. What is a compound?
A pure substance made of 2 or more elements in defined proportion
For example:
H2O is always 2 hydrogens and 1 oxygen
NaCl is always 1 sodium and 1 chlorine

3. 2 Types of Compounds Ionic Covalent Involves ionic bonding
2 elements trade electrons to become ions
Covalent
Involves covalent bonding
2 elements share electrons

4. Anatomy of Ionic Compounds
Every ionic compound is made of an anion and a cation.
The attraction between positive and negative ions is called ELECTROSTATIC FORCE.
This force creates IONIC BONDS.

5. Structure of Ionic Compounds
Anions & cations stack together in a 3-d pattern called a crystal lattice.
The lattice is held together by electrostatic forces.
The pattern created by the ions is designed to balance charge.

6. More on Anions & Cations
Lost electrons and have a positive charge.
Usually metals (less than 4 valence electrons).
Anions:
Gained electrons and have a negative charge.
Usually nonmetals (more than 4 valence electrons).
Can be a polyatomic ion.

7. Ionic Formulas Fact: Charges NEED to be balanced.
Atoms: Protons = Electrons
Ionic Compounds: + Charge = - Charge
Goal: Total positive charge = total negative charge = Zero
This is called balancing the formula.

8. How to Balance A Formula
Add the charge of the cation and anion.
If the sum is zero, the formula is already balanced so write the cation first then the anion.
HINT: Positive before negative!!!

9. Example Na+1 and Cl-1 (+1) + (-1) = 0 Already Balanced!!!
NaCl is the formula

10. How to Balance A Formula
Add the charge of the cation and anion.
If the sum is not zero, add cations or anions to make the sum zero.
This is a trial and error process.
When balanced, write the cation first, then the anion. Use subscripts to indicate how many of each ion are needed.

11. Example Na+1 and P-3 (+1) + (-3) = -2 Not Balanced!!! Add 2 more Na+1
Na+1, Na+1, Na+1 and P-3
Check: (+1) + (+1) + (+1) + (-3) = 0
Na3P is the formula

12. Monoatomic Ions All the ions you have seen so far are monoatomic
Monatomic = made of 1 atom
Na+, Br-1, Al+3 and so on….

13. Polyatomic Ions Polyatomic = made of more than 1 atom
These are special ions.
Made of atoms COVALENTLY bonded together that as a group have an overall charge
SO4-2, PO4-3 (these are on the back of your periodic table)

14. What to do with Polyatomic Ions
Treat Polyatomic Ions like a normal ion, as one unit.
Rules:
If more than one polyatomic ion is needed put parentheses around it & subscript outside
NEVER change a polyatomic ion formula
Example: Mg+2 + OH-1
I need twp OH- ions to balance out the Mg+2 ion. I write the compound as Mg(OH)2,
not MgOH2 or MgO2H2