Chemical Bonding And Molecular Structure

- Underlining similarity in different problems.
1
Pattern: Problems based on formal charge Description: In such problems, a molecule may be given and we need to calculate formal charge of each atom. How to approach:
  1. Draw Lewis dot structure of the molecule given.
  2. Write the valence electrons of the target atom.
  3. Subtract bonding and non-bonding electron from the valence electron of a molecule whose formal charge is to be calculated, using the formula below:
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2
Pattern: Problems based on resonance structure Description: You may get questions where you are asked to identify the resonating structures of draw out the resonating structure of a given molecule. How to approach: To solve questions, you should be able to draw the Lewis structure. Once the Lewis structure is drawn, you need to check if there is more than one way to place the double bonds and lone pairs on atoms. Also, make sure that the octet rule is followed in all the structures. You can practice these questions on the topic:
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3
Patterns: Problems based on Fajan's rule Description: The questions are based on arranging polar covalent molecules on the basis of their polarizability of anion and polarising power of cation. How to approach:
  1. Check the polarising power of cation. If the cation is small its polarising power is high as well as covalent character is high.
  2. Check the polarizability of an anion. If the anion is large it has loosely bound electrons in its outermost orbit which can easily form a stronger covalent bond with the anion. which increases its covalent character.
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4
Pattern: Problems based on predicting geometry of molecule using VSEPR theory Description: The questions are based on predicting the geometry of a molecule on the basis of their lone pair-lone pair, bond pair- bond pair and lone pair-bond pair repulsion. How to approach:
  1. Count the lone pairs and bond pairs present in the hybridization.
  2. Match the values as per the table below and find out the geometry.
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5
Pattern: Problems based on molecular orbital theory: Description: The molecules are given in such a way that sometimes they want you to calculate bond order separately and electronic configuration separately. Sometimes a combined question also there. How to approach:
  1. Draw the molecular orbital diagram of the respective molecule.
  2. Draw its electronic configuration on the basis of bonding and antibonding molecular orbitals.
  3. Use the formula shown below.
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