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Write notes on (a) Bond Angle (b) Bond Enthalpy (c)Bond length and (d) Bond order. |
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Answer» Solution :a) Bond angle : The angle between the orbitals containing bonding electron pairs around the central atom in a molecule, COMPLEX ION is called bond angle. Bond angle is expressed in degrees. i) Bond angle depends on the presence of lone pair electrons with increase in the number oflone pairs the bond angle decreases. eg. in the molecules which contain four electron pairs the bond angles are follows.  ii) Bond angle decreases with increase in the electronegativity with increase in the electronegativity of central atom. eg.  iii) Bond angle depends on the hybridisation.  b) Bond enthalpy : The AMOUNT of energy required to break one mole of bonds of a particular type between two at atoms in a gaseous state is called bond enthalpy. More is the bond enthalpy, stronger the bond and more is the STABILITY of the molecule. In the case of poly atomic molecules the bond enthalpy is the average of the similar bond ENTHALPIES is taken. eg. in `H_(2)O` to break the two O - H bonds is not same. The energy required for breaking first bond is 502 kJ `mol^(-1)` and for the second bond is 427 kJ `mol^(-1)`. So the average value 464.5 kJ `mol^(-1)` is considered as the bond enthalphy. c) Bond length : It is defined as the equilibrium distance between the nuclei of two bonded atoms in a molecule. Bond length is equal to the sum of the covalent radii of two similar atom in the bond. In hetero atomic molecules the bond length can be calculated using the formula. `d_(AB)=r_(A)+r_(B)+c(X_(A)-X_(B)). " Where " X_(A) " and " X_(B)` are the electronegativities of atom A and B. The value of C depends on the nature of atoms participating in the bond. Bond lengths depend on the number of bonds between atoms, type of hybridisation etc. d) Bond order : It is defined as the number of bonds between the two atoms in a molecule. Eg : Bond orders in `H_(2)` is 1, `O_(2)` =2 and `N_(2)` = 3. In the resonance hybrid the bond order `="No. of bonds around the central atom"/"No. of atoms around the central atom"` In cyclic compounds, the bond order is `="No. of bonds in the ring"/"No. of atoms forming the ring"` Isoelectronic molecules and ions have identical bond orders. e.g. `F_(2) " and " O_(2)^(2-)` have bond order 1. `N_(2)`, CO and `NO^(+)` have bond order 3. More the bond order more is the bond enthalpy, lesser the bond length, more the stability. |
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