Find the element’s atomic number
Write its electronic configuration
Count the electrons in the outermost shell
If outermost electrons are 1, 2, or 3, valency = 1, 2, or 3
If outermost electrons are 5, 6, or 7, valency = 8 minus outermost electrons
If outermost electrons are 4, valency = 4
If outermost shell is complete with 8 electrons, valency = 0
For transition elements, check the common oxidation states
Use the most common combining capacity as the valency