Important questions based on NCERT syllabus for Chapter 4 - Chemical Bonding and Molecular Structure:
Question-1: Define Octet rule. Write its significance and limitations.
Solution: Octet rule: Atoms of elements combine with each other in order to complete their respective octets so as to acquire the stable gas configuration.
Significance: It helps to explain why different atoms combine with each other to form ionic compounds or covalent compounds.
Limitations of Octet rule:
According to Octet rule, atoms take part in chemical combination to achieve the configuration of nearest noble gas elements. However, some of noble gas elements like Xenon have formed compounds with fluorine and oxygen. For example: XeF2, XeF4 etc. Therefore, validity of the octet rule has been challenged. This theory does not account for shape of molecules.
Question-2: Although both CO2 and H2O are triatomic molecules, the shape of H2O molecule is bent while that of CO2 is linear. Explain this on the basis of dipole moment.
Solution: In CO2, there are two C=O bonds. Each C=O bond is a polar bond.
The net dipole moment of C02 molecule is zero. This is possible only if CO2 is a linear molecule. (O=C=O). The bond dipoles of two C=O bonds cancel the moment of each other.Whereas, H2O molecule has a net dipole moment (1.84 D). H2O molecule has a bent structure because here the O—H bonds are oriented at an angle of 104.5° and do not cancel the bond moments of each other.
Question-3: Write the significance/applications of dipole moment.
In predicting the nature of the molecules: Molecules with specific dipole moments are polar in nature and those of zero dipole moments are non-polar in nature.
In the determination of shapes of molecules.
In calculating the percentage ionic character.