The molecular formula describes a substance’s composition and bond structure, but some materials cannot be accurately represented. Atoms bond to form molecules, and the molecular formula represents the elemental composition. Empirical formulas are the smallest repeating unit of a molecule. Molecular formulas are used to calculate molecular weights, but they are not a direct measure of density, mass, or state of being. Macromolecules are difficult to characterize by their molecular formulas. Polyethylene has a repeating unit of (CH2)n.
The molecular formula is a notation used to describe the composition of a substance. Most of the formulas are written in a way that they also give some detail about the bond structure of the material. A related notation includes empirical formulas. Some materials cannot be accurately represented by the use of molecular formulas.
Matter is made up of atoms, the smallest amount of mass that retains chemical properties when broken down. Atoms bond in different ways to form molecules. A molecular formula represents the elemental composition of a molecule.
The molecular formula of water is H2O. The number two indicates two hydrogen atoms in the molecule. The O appears without a number, signifying an oxygen atom. Depending on the text, numbers may be written without subscript. Handwritten formulas always use subscript.
Propane is a component of natural gas. This hydrocarbon has three carbon atoms with linear bonds forming a straight chain. The carbon chain is surrounded by eight hydrogen molecules. The molecular formula is C3H8. In the refining process, some of the propane will react to form cyclopropane. Cyclopropane is a triangular molecule surrounded again by six hydrogen atoms, with the molecular formula C3H6.
One hydrogen molecule, H2, was lost in the production of cyclopropane. Other reactions were possible, including the loss of a hydrogen molecule between two of the three carbon atoms. Propene, which has a double bond between the first and second carbons, also has a molecular formula of C3H6. While the formula of C3H8 must be propane, C3H6 is insufficient information to identify the compound.
The empirical formula is written as the smallest repeating unit of a molecule. The notation requires subscripts in the formula to be positive integers. The molecular and empirical formulas for glucose are C6H12O6 and CH2O, respectively. In this case, six empirical glucose formulas are needed to construct the molecule. Empirical formulas can be considered the lowest common denominator.
Molecular formulas are used to calculate the molecular weights of materials, which in turn provide the values for determining the number of molecules or ions present in a given mass of material. These calculations are needed to evaluate the results of a reaction or to prepare a solution of known concentration. Molecular formulas are not a direct measure of density, mass, or state of being.
Macromolecules, both natural and synthetic, are difficult to characterize by their molecular formulas. These long chain molecules often have branch points with their own long chains. Typically, the monomer, or starting chemical from which the polymer was derived, is used as a pseudo-molecular formula. Polyethylene is made by removing a hydrogen molecule from ethane to form ethane which then polymerizes. It has a repeating unit of (CH2)n, n being an unknown but large number.
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