1. Writing Formulas for Binary Ionic Compounds
Example 5
Here’s another example of writing the formula for an ionic compound.

2. Ca2+ P3– Ca2+ P3– F– Ca2+ Ca3P2 +2 –3
Write the formula for the compound barium selenide.
Ca2+
P3–
Ca2+
P3– F–
Ca2+ +2 –3
Ca3P2
In this example, we’re asked to write the formula for the compound barium selenide.

3. Write the formula for the compound barium selenide.
We find the elements on the periodic table. We see that barium is a metal whose ion has a charge of positive 2

4. Write the formula for the compound barium selenide.
We find an element that sounds like selenide but doesn’t end in –ide.

5. Write the formula for the compound barium selenide.
It is the non-metal selenium, whose ion has a charge of negative 2.

6. Ba2+ Se2– Write the formula for the compound barium selenide.
This compound contains the ions Ba two plus and Se 2 minus.

7. Ba2+ Se2– +2 –2 Write the formula for the compound barium selenide.
Total Positive Charge
Total Negative Charge
With one barium ion and one selenide ion, the total positive charge is positive 2 and the total negative charge is negative 2.

8. Ba2+ Se2– +2 –2 Write the formula for the compound barium selenide.
Total Positive Charge
Total Negative Charge
These DO add up to zero
The two charges positive 2 and negative 2 are balanced already. They do add up to zero.

9. Write the formula for the compound barium selenide.+2 –2
BaSe
One barium ion will simplycombine with one selenide ion and result in the formula BaSe.

10. Ba2+ Se2– BaSe +2 –2 Formula:
Write the formula for the compound barium selenide.
Ba2+
Se2– +2 –2
BaSe
Formula:
We’ve now answered the question, the formula for barium selenide is simply BaSe, with no subscripts Again, we see that no charges are written in the final formula for a compound.