1. Formula Writing
Say what??

2. Formula Writing Ionic Compounds
One metal + one non-metal

3. Let’s Review
Fill in the charges

4. More Review
How are ions formed?
Positive ions –
Aka:
Negative ions –

5. Lets Write Some Formulas…
Positive ions are ALWAYS written first.
If more than one ion can exist, use parentheses and the charge in roman numeral form
Ie: Cu+2 is named copper (II)
These are called multivalent ions.
Negative ions are ALWAYS written second.
So…
Can two positive ions ever be put together?
Can two negative ions ever be put together?

6. How do you know what numbers to use?
Criss-Cross Method
Identify the charge of each ion
“criss-cross” the charges  ignore the + and –
Numbers become subscripts for other element
Let’s do a few examples… pick any cation and anion:

7. Naming Compounds Cation stays the same Anion ending changes to –ide
Often this simply involves changing the –ine ending
Chlorine  chloride
Fluorine  fluoride
Bromine  bromide
However, there are some you need to remember:
Examples:
Phosphorus  phosphide
Sulfur  sulfide
Oxygen  oxide

8. Let’s do some more practice…
Charges Criss Cross Name
Ca and Cl
Ba and O
Cu and I

9. Formula Writing Polyatomic Ion Compounds

10. Polyatomic Ions Remember: New: Cation (positive ion) is written first
Anion (negative ion) is written second
New:  
Put parentheses around the polyatomic ion ALWAYS

11. Naming the Compounds with Polyatomics
You need to recognize the Polyatomic Ions
If monoatomic ion: cation and anion is the same
If polyatomic ion: use names provided

12. Some Polyatomic Practice
Write the formula the following:
Formula Name
 Ba C2H3O2 -1 ________________ _____________________
Al PO4 -3 ________________ _____________________
 K SO4 -2 ________________ _____________________
Ca NO3 -1 ________________ _____________________

13. Formula Writing Covalent Molecules
2 non-metals together

14. Writing Formulas Remember, bonds require 2 electrons
Covalent is the sharing of electrons

15. Naming Covalent Compounds
The less electronegative element is written first.
Remember the trend (increasing up and to the right)
Use a number indicating prefix only if more than one atom is present
Ie N2 is dinitrogen
A prefix is always added to the name of the second element
Will change ending of name to –ide (just like ionic bonds)

16. Naming Covalent Compounds - Rules
Leave the "a" off the end of the prefixes that end in "a" and the “o” off of mono-if they are placed in front of an element that begins with a vowel.
Number Indicating Prefixes:
mon(o) -1
hex(a) - 6
di -2
hept(a) - 7
tri -3
oct(a)- 8
tetr(a) - 4
non(a) -9
pent(a) -5
dec(a) -10

17. Try Some Practice
N2S4
NI3
CCl4
P2O5

18. Try Some Practice ~ ANSWERS
NI3
CCl4
P2O5
Dinitrogen tetrasulfide
Nitrogen triiodide
Carbon tetrachloride
Diphosphorus pentoxide

19. Common Names H2O - water NH3 - ammonia CH4 - methane C2H6 - ethane
C3H8 - propane