Types of Chemistry Formulas

• There are three main types of chemical formulas: empirical formulas, molecular formulas and structural formulas. Which type of chemical formula you want to use depends on the situation. Empirical formulas are good if you are only interested in the ratio between the atoms. Molecular formulas are used if you need to know how many atoms of each element are present in one molecule of a compound. Structural formulas are used to explain the exact order of bonding between the elements.
  
  

Empirical (Simple) Formula

• Sometimes you are only interested in how many atoms of one element combines with how many atoms of another element to form a compound. This is the main purpose of an empirical formula. It provides you with simple information and not too much (and often irrelevant to the situation) detail. To find the empirical formula for a compound you can look at the ratio between the elements. In sulfur dioxide there is one sulfur atom to every 2 oxygen atoms. The empirical formula of sulfur dioxide is therefore SO2. This is the lowest possible integer formula that keeps the ratio constant. If you have a formula of C2H6 (ethane) and you want its empirical formula, you divide the larger number (6) by the lower(2) to get CH3. This is the empirical formula of ethane.
  
  

Molecular (Normal) Formula

• When you want more detail about a chemical compound, you often start with the molecular formula. This formula tells you exactly the number of different atoms that are present in one molecule of the compound. From this information you can find the molecular mass of the compound, which is how much one molecule weighs. In addition, if you have a sample then you can weigh it and by using the molecular formula calculate exactly how many molecules are in the sample. This cannot be done with an empirical formula and it demonstrates the abilities of a mere molecular formula. C2H6 is the molecular formula of ethane, and says that in one molecule of ethane there are 2 carbon and 6 hydrogen atoms.
  
  

Structural (Extensive) Formula

• Structural formulas show every single bond in a molecule. In a structural formula you list the elements in their bonding order, and you include any single or double bonds as well as lone pairs of electrons. This type of formula is best used when you need to know the exact details of a molecule, for instance if you are looking at molecular shape. To get the molecular shape of a molecule you need to know the bonding and lone electron pairs to great detail, and from the structural formula you can then derive the actual shape of the molecule.