Types of Chemical Formulae.

Types of Chemical formulae for Organic Compounds namely Molecular Formula,Structural Formula,Condensed Formula & Dot and Cross Formula are discussed with examples.

1. There are four types of formulae of Organic compounds: 1. Molecular formula 2. Structural formula 3. Condensed formula 4. Dot and Cross formula

2. 1. Molecular formula The molecular formula of Butane is C 4 H 10 . It also shows that the molecule of Butane has 4 Carbon (C) atoms and 10 Hydrogen (H) atoms. This formula shows that the molecule of Butane is made up of Carbon (C) and Hydrogen (H) atoms.

3. Consider another example of Water : The molecular formula of Water is H 2 O . It also shows that the molecule of water has 4 Carbon (C) and 10 Hydrogen (H) atoms. This formula shows that the molecule of water ( i -e H 2 O) is made up of Hydrogen (H) and Oxygen (O) atoms. From these examples it is clear that a molecular formula shows: the atoms present in the molecule and their number ( i -e How many of these atoms are present) .

4. 2. Structural formula As discussed earlier, the molecular formula of Butane is C 4 H 10 . This formula doesn't tell us the a rrangement of atoms in the molecule. By seeing the molecular formula, we only know that Butane contains Carbon and Hydrogen and that there are 4 Carbon and 10 Hydrogen atoms. But, How are these atoms arranged? What is there structure? These Questions remain unanswered in the molecular formula. To represent the structure of a molecule we use “structural formula”. So, Method to represent Bonds: Atoms in a molecule are connected to each other by Bonds . These Bonds may be single, double or triple. In a structural formula, single bond is represented by a single line ( ) , a double bond by two lines ( ) and a triple bond by three lines ( ) between the bonded atoms.

5. Examples: Let us see the structural formula of methane (CH 4 ). C H H H H This is the Structural formula of Methane. Now, l et us see the structural formula of ethane (C 2 H 6 ). C H H H C H H H This is the Structural formula of Ethane. These structural formulae show how the atoms are connected with each other. By simply seeing CH 4 or C 2 H 6 ( i -e molecular formulae) we don’t know how the atoms are connected , neither do we know which bonds are present (single, double or triple).

6. Concept related to bonds. C This is a Carbon Atom. It has 6 electrons. Its Electronic Shell Configuration is : K-Shell 2 L-Shell 4 N Nucleus L - Shell K - Shell Electrons Carbon Atom So, the outer shell of C has 4 electrons. H This is a Hydrogen Atom. It has 1 electron. Its Electronic Shell Configuration is : K-Shell 1 So, the outer shell of H has 1 electron only. As Carbon has 4 electrons in its outermost shell w hile hydrogen has 1 electron in its outermost shell, so 4 Hydrogen atoms will form bonds with 1 Carbon atom. H H H

7. The formula that indicates the group of atoms joined together to each carbon atom in a straight chain or a branched chain is called the condensed formula. 3. Condensed formula: C H H H C H H H 2 3 2 3 This is the condensed formula of Ethane. To write the condensed formula ,first of all write the structural formula. Consider , Ethane ( CH 4 )

8. 4. Dot and Cross formula The formula which shows the sharing of electrons between various atoms in one molecule of the organic compound is called dot and cross formula or electronic formula. C This is carbon, with its four electrons represented by dots ( ) . H This is hydrogen, with its one electron represented by cross ( ) . To form methane Carbon needs 4 Hydrogen atoms. H H H Consider, Methane. This is the Dot and cross formula for Methane.