If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

### Course: Chemistry library>Unit 3

Lesson 4: Molecular composition

# Empirical, molecular, and structural formulas

There are three main types of chemical formulas: empirical, molecular and structural. Empirical formulas show the simplest whole-number ratio of atoms in a compound, molecular formulas show the number of each type of atom in a molecule, and structural formulas show how the atoms in a molecule are bonded to each other. Created by Sal Khan.

## Want to join the conversation?

• what's the meaningo of those double bonds ?
• A double bond is where there are four electrons shared between two atoms. You will learn more about these in future videos.
• We are taught in our school that the chemical formula of bleaching powder is CaOCl2, but checking it on Internet I came across the chemical formula to be Ca(OCl)2.
So which among the two is correct ? Please give the chemical structure of bleaching powder too.
• The parenthesis in chemical formulas are from things called polyatomic ions. They’re basically groups of atoms with shared charges (mini molecules inside of molecules). The chemical formula CaOCl2 refers to one calcium atom, one oxygen atom, and two chlorine atoms. The formula Ca(OCl)2 refers to one calcium atom, two oxygen atoms, and two calcium atoms (two groups of calcium and oxygen atoms bonded).
• how do you actually calculate the empirical formula?
• Around , Sal says that the empirical formula is a ratio of 1:1.
If the ratio of Carbon to Hydrogen were something like 2:3, how would you write it? Cv2Hv3? It would look exactly like a molecular formula!
• At can we say that for every oxygen, we have two hydrogen?
• Yes, entirely correct. 2H per 1O, or otherwise 1O per 2H
• what would the ratio look like if you were given a formula of 3 different elements?
• Here is an example. Glucose has the molecular formula C6H12O6. Its empirical formula is CH2O. Thus C, H and O are in the ratio of 1:2:1 .
• How do you depict Benzoic acid as a molecular and empirical formula?
• The following is the answer to your question. It's a molecular formula that can be written as C₆H₅CO₂H or C₇H₆O₂.
I Hope this Helps!
• I could not exactly understand the difference between the molecular formula and empirical formula? Could anybody please explain?
• Molecular formula shows exactly how many of each atom there is, while empirical formula shows the ratio. Sometimes the empirical and molecular formula are the same, like with water.
(1 vote)
• how to find the molecular formula like when calcium carbonate is equal to caco3
• Note that CaCO3 is an ionic compound. For ionic compounds, the empirical formula is also the molecular formula. As ionic compounds generally occur in crystals that vary in number of groups of empirical units, the molecular formula is the empirical formula.

Put another way, ionic compounds are never made of lone molecules. Empirical formulae, which relate atoms in compounds, would be the same as the molecular formula, which relates the ions in the compound.

In sum, CaCO3 is the molecular formula too. It's the same for all ionic compounds.

Hope that helps.
(1 vote)
• I know this maybe a dumb question but what are double bonds?