Structural Formula of Carbon Compounds

  1. A molecular formula is a chemical formula which shows the actual number of atoms of each element present in one molecule of a substance
  2. A structural formula is a chemical formula which shows the arrangement of the atoms in a molecule of a substance.

Writing the Structural Formulae

Rules to be followed:

  1. All atoms are bonded together by covalent bond represented by a straight line. The bond can be a single bond, a double bond or a triple bond.
  2. The number of covalent bonds at each atom is as follow:
    1. Hydrogen: 1 
    2. Carbon: 4
    3. Oxygen: 2
Steps to be followed:

Step 1: Determine the number of carbon in the molecule (Let’s say 3 carbon atom)
Step 2: Draw all the carbon atoms in a straight line and then draw the covalent bonds to connect all the carbon atoms.

Step 3: Draw additional single covalent bonds on each

Step 4: Write the hydrogen atoms

Step 5: Check that each carbon atom has four single covalent bonds, each hydrogen atom has one single covalent bond.

Isomerism

  1. Isomers are compounds with the same molecular formula but different structural formulae.
  2. Isomerism is the existence of two or more compounds that have the same molecular formula but different structural formulae.
    Examples of two isomers of butane

    (The 2 molecules have same molecular formulae but different structural formulae)
  3. Isomers have different physical properties because they have different molecular structures.
  4. However, isomers have the same chemical properties because they belong to the same homologous series.