1. Writing Formulas
Chemistry
Mrs Stoops

2. Finding the charge (General only)
Na has a Dot diagram of: Na
So to become more stable, and form an ion it will LOSE 1 electron
Na+1
Mg has a Dot diagram of: Mg
So to become more stable, and form an ion it will LOSE 2 electrons
Mg+2

3. SO, Cl Cl-1 S S-2 Cl has a Dot diagram of:
(General only)
Cl has a Dot diagram of: Cl
So to become more stable, and form an ion it will GAIN 1 electron
Cl-1 S
S has a Dot diagram of:
So to become more stable, and form an ion it will GAIN 2 electrons
S-2
SO,

4. There is a PREDICATBLE pattern+1
You need to memorize this +2 +3
+/-4 -3 -2 -1 +1 +2

5. POLYATOMIC IONS Groups of atoms with a charge
NEED to memorize name, symbol, and charge they have
There are 12
Acetate = C2H3O2 -1
Chlorate = ClO3-1
Cyanide = CN-1
Hydroxide = OH-1
Nitrate = NO3-1
Nitrite = NO2-1
Carbonate = CO3-2
Chromate = CrO4-2
Sulfate = SO4-2
Sulfite = SO3-2
Phosphate = PO4-3
Ammonium = NH4+1

6. Rules for Writing Formulas
Formulas always have a positive and negative part
Formulas always have the positive part first
Chemists don’t write the number 1
Formulas use whole numbers only
Formulas are simplified and reduced when possible
Add parentheses when we need more than one polyatomic ion (When a polyatomic has an extra subscript)
Formulas will have NO OVERALL charge.

7. How to write formulas “Criss Cross” method
Steps:
1. Write the positive part first with the charge and the negative part second (w/ charge)
2. Cross charge number only – Take the charge number from the “attic” and put it in the “basement” of the OTHER element.
3. Erase the original charges
4. Simplify.

8. Example Ca & Cl “what are the charges?” Ca +2 Cl-1 “cross the charge
number”
Ca +2
Cl-1
Ca +2 1
Cl-1 2
“erase charges”
Ca 1
Cl 2
“reduce simplify”
CaCl2

9. Example “cross the charges” “reduce simplify” Al OH
“what are the charges?”
Al+3
OH-1
“cross the charges” Al
OH3
What is wrong with this?
“reduce simplify”
Al(OH)3

10. #2
Sn+4
O-2
Sn2O4
SnO2

11. #3 Mg
PO4
Mg3(PO4)2

12. #4
NH4
CO3
(NH4)2CO3