Name:
Period:
Date:
Review: Writing Chemical Formulas
Objective 3-3: SWBAT write the formula of an ionic compound.




The octet rule tells us that atoms want to have a full octet. In
order to do this, they must GAIN or LOSE valence electrons to
form IONS.
It is difficult to always carry a charge, so ions try to bond with an
atom that has an OPPOSITE charge.
Sometimes, this means that multiple atoms must bond to even
out the charges (see Figure 1).
Chemical formulas tell us the NUMBER and TYPE of atoms in a
compound.
1
Figure 1
ion bonds with
2 F- ions
Mg2+
Steps to Write a Chemical Formula:




Step 1: Write the element symbols. The cation always goes first!
Step 2: Determine the charge for each ion and write it as a superscript.
Step 3: Criss-cross the charges and remove the sign to create the subscripts of the chemical
formula.
Step 4: Simplify if necessary.
Example: Zn2+ and NO3-  Zn(NO3)2
How to Find the Charge of a Transition Metal:



You need to notice the subscript of the transition metal, subscript of the anion, and CHARGE of the
anion.
Multiply the subscript of the anion by the charge of the anion.
Divide by the subscript of the transition metal.
Formula: subscript of anion x charge of anion / subscript of transition metal = charge of transition metal
Example: Zn(NO3)2  nitrate is (NO3)-  2 x 1 / 1 = 2  zinc is Zn2+
Practice
Directions: Write the chemical formula for the ionic compound that would form.
1. Magnesium and bromine
5. Fluorine and strontium
2. Phosphorous and potassium
6. Boron and nitrogen
3. Calcium and chlorine
7. Caesium and oxygen
4. Aluminum and selenium
8. Copper (2+) and chlorine
9. Nitrogen and lead (4+)
15. Ammonium and selenium
10. Zinc (2+) and sulfur
16. Copper (2+) and hydroxide
11. Titanium (4+) and oxygen
17. Al3+ and F-
12. Phosphorous and cobalt (2+)
18. N3- and Ca2+
13. Magnesium and nitrate
19. (NH4)+ and O2-
14. Aluminum and sulfate
20. Co4+ and (SO4)2-
Directions: Find the charge of the transition metal.
21. Mn2O3
28. TiCl4
22. TiS2
29. CuPO4
23. PbN2
30. Fe2O3
24. CoCO3
31. Ag2O
25. CuSO4
32. AgO
26. NiCl2
33. CuCl2
27. VF5
34. SnBr3