Types of Chemical Formulae.
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The document describes four types of formulae for organic compounds: molecular, structural, condensed, and dot and cross formulae. It explains how the molecular formula indicates the types and numbers of atoms in a molecule, while structural formulas reveal the arrangement and bonding of those atoms. It also distinguishes condensed formulas, which group atoms together, and dot and cross formulas, which illustrate electron sharing among atoms.
Types of Chemical Formulae.
- 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 C4H10 . This formula shows that the molecule of Butane is made up of Carbon (C) and Hydrogen (H) atoms. It also shows that the molecule of Butane has 4 Carbon (C) atoms and 10 Hydrogen (H) atoms.
- 3. Consider another example of Water : The molecular formula of Water is H2O . This formula shows that the molecule of water (i-e H2O) is made up of Hydrogen (H) and Oxygen (O) atoms. It also shows that the molecule of water has 4 Carbon (C) and 10 Hydrogen (H) atoms. From these examples it is clear that a molecular formula shows: 1. the atoms present in the molecule 2. 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 C4H10 . This formula doesn't tell us the arrangement 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”. 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 (CH4). H H C This is the Structural formula of Methane. H H Now, let us see the structural formula of ethane (C2H6). H H C C H 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 CH4 or C2H6 (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. This is a Hydrogen Atom. It has 1 electron. Its Electronic Shell Configuration is : This is a Carbon Atom. It has 6 electrons. Its Electronic Shell Configuration is : K-Shell 1 K-Shell 2 L-Shell 4 So, the outer shell of C has 4 electrons. Nucleus So, the outer shell of H has 1 electron only. Carbon Atom N L - Shell K - Shell As Carbon has 4 electrons in its outermost shell while hydrogen has 1 electron in its outermost shell, so 4 Hydrogen atoms will form bonds with 1 Carbon atom. Electrons
- 7. 3. Condensed formula: 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. Consider , Ethane (CH4) To write the condensed formula ,first of all write the structural formula. H H H C 2 3 C H H H 3 2 This is the condensed formula of Ethane.
- 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. Consider, Methane. This is the Dot and cross formula for Methane. This is carbon, with its four electrons represented by dots ( ) . To form methane Carbon needs 4 Hydrogen atoms. This is hydrogen, with its one electron represented by cross ( ) .