1. Ch. 5 - Ionic Compounds

2. Writing a Formula Cl BaCl2
Write the formula for the ionic compound that will form between Ba2+ and Cl.
Solution:
1. Write the positive ion of metal first, and then write the negative ion next.
Ba Cl
2. The charges have to add up to zero.
Cl
3. Write the number of ions needed as subscripts.
Don’t show charges in the final formula.
BaCl2

3. Write the formula for calcium chloride.
Writing Formulas
Write the formula for calcium chloride.
Calcium is Ca2+
Chloride is Cl-
Ca2+ Cl- would have a +1 charge.
Need another Cl-
CaCl2

4. Learning Check
Write the correct formula for the compounds containing the following ions:
A. Na+, S2-
Na2S
B. Al3+, Cl-
AlCl3
C. Mg2+, N3-
Mg3N2

5. Learning Check A. The formula for the ionic compound of Na+ and O2- is
Na2O
B. The formula of a compound of aluminum and bromine is
AlBr3
C. The formula of Fe3+ and O2- is
Fe2O3

6. Ionic Formulas If charges cancel, just write symbols.
If not, use subscripts to balance charges.