Writing chemical formulas is an essential skill in the event that you will be successful in chemistry. Balancing equations, predicting reactions and calculating stoichiometric problems all rely in your power to properly write a chemical formula. If you produce a mistake in the formula it will affect the balancing and the mole ratios used to do stoichiometric calculations. So take a moment to discover ways to properly write chemical formulas, you'll be glad you did.
What You Have to Know...
- Just how to use the Periodic Table
- How to use subscripts
- How to ascertain ionic charges
- Polyatomic ions
- Metals with multiple charges
- Greek and Latin numeric prefixes
The General Rule
Most compounds contain two parts (binary) and are classified as ionic or covalent. The overall rule for naming and writing compounds is to put the more metallic element first followed closely by the less metallic element. Remember to use subscripts to show how many atoms or ions present in the formula.
Writing Ionic Formulas
When writing the chemical formula for ionic compounds place the cation first, then your anion and check to see that the charges balance to zero. If the charges aren't balanced, you should increase how many cations and anions before the algebraic sum of the charges is zero.
- If the charges are (2+) and (3-) the sum is (1-) and isn't balanced. But the lowest common multiple of 2 and 3 is 6. So using subscripts increase how many cations by 3 and how many anions by 2.
- Thus (2+) times 3 is (6+) and (3-) times 2 is (6-) and (6+) + (6-) is zero. Balanced.
If the cation has multiple charges, the correct charge is indicated with a Roman numeral placed after the cation's name. Remember to treat polyatomic ions as complete unit, don't separate them.
EXAMPLE #1: calcium chloride is CaCl2 (calcium 2+) (chlorine 1-) boost the chlorine to two.
EXAMPLE #2: lithium nitrate is LiNO3 (lithium 1+) (nitrate 1-) balanced.
EXAMPLE #3: iron (II) sulfate is FeSO4
Writing Molecular Formulas (covalent)
When writing the chemical formula for covalent compounds place the less electronegative element first followed closely by the more electronegative element and use subscripts to indicate how many atoms present. CAS NO.174063-87-7 Remember that prefixes are employed only with covalent compounds.
EXAMPLE #1: co2 is CO2 (1 C) (2 O)
EXAMPLE #2: phosphorous pentachloride is PCl5 (1 P) (5 Cl)
Don't Forget to Practice
Really, that's all there is to writing chemical formulas. Now you need to practice, practice and practice some more. Although chemical formulas aren't all that hard, you'll need to practice in the event that you will be any good at it.