Here’s another example of writing the formula for an ionic compound.

Writing Formulas for Binary Ionic CompoundsExample 5

In this example, we’re asked to write the formula for the compound barium selenide.

Ca2+ P3–

F–Ca2+

Ca2+

+2 –3Ca3P2

P3–

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

Write the formula for the compound barium selenide.

We find an element that sounds like selenide but doesn’t end in –ide.

Write the formula for the compound barium selenide.

It is the non-metal selenium, whose ion has a charge of negative 2.

Write the formula for the compound barium selenide.

This compound contains the ions Ba two plus and Se 2 minus.

Write the formula for the compound barium selenide.

Ba2+ Se2–

With one barium ion and one selenide ion, the total positive charge is positive 2 and the total negative charge is negative 2.

Write the formula for the compound barium selenide.

Ba2+ Se2–

+2 –2Total Positive Charge

Total Negative Charge

The two charges positive 2 and negative 2 are balanced already. They do add up to zero.

Write the formula for the compound barium selenide.

Ba2+ Se2–

+2 –2Total Positive Charge

Total Negative Charge

These DO add up to zero

One barium ion will simplycombine with one selenide ion and result in the formula BaSe.

Write the formula for the compound barium selenide.

Ba2+ Se2–

+2 –2

BaSe

Write the formula for the compound barium selenide.

Ba2+ Se2–

+2 –2

BaSeWe’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.

Formula: