# How do you determine the formula of an ionic compound?

May 23, 2018

Example #1 write the chemical formula for Calcium Oxide

Step 1
-Find the Atomic symbol of the metal and non-metal on the periodic table
CaO

Step 2

Find the charges for Calcium and Oxygen

which are Ca 2+ and O 2-

Step 3

Balance out the charges

Here´s the chemical formula for Calcium Oxide

CaO

Example 2 write the chemical formula for Aluminum Oxide

Step 1

-Find the Atomic symbol of the metal and non-metal on the periodic table

$A l O$

Step 2

Find the charges for Aluminum and Oxygen

Which are Al 3+ and O 2-

Step 3

Balance out the charges

You need 2 Aluminum and 3 Oxygen to balance the charges

Al 3+ O 2-
Al 3+ O 2-
= 6 + O 2-
= 6-

Step 4

If you need more then one element to balance out the charges you identify that by using subscripts

Heres your chemical formula for Aluminum Oxide

$A {l}_{2} {O}_{3}$

Best Of Luck

-AN