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4.40     What is meant by the term bond order? Calculate the bond order of :

$N_{2}$

$O_{2}$,

$O_{2}^{+}$

$O_{2}^{-}$

Bond order (B.O.) is defined as one half the difference between the number of electrons present in the bonding and the antibonding orbitals of a molecule. Where  are the number of electrons occupying bonding orbitals and the number occupying the antibonding orbitals respectively.  So, bond order for different molecules are:  : The electronic configuration is  Where, the number of bonding...

4.39     Define hydrogen bond. Is it weaker or stronger than the van der Waals forces?

Hydrogen bond can be defined as the attractive force acting between the hydrogen atom of one molecule with the electronegative atom (F, O or N) of another molecule. Because of the difference between electro-negativities, the bond pair between hydrogen and the electronegative atom gets drifted towards a more electronegative atom. As a result, the hydrogen atom becomes slightly positively...

4.38     Describe the hybridisation in case of  $PCl_{5}.$ Why are the axial bonds longer as compared to equatorial bonds?

The initial ground state and final excited state electronic configuration of phosphorus (P) are: So, the phosphorus atom is  hybridized in the excited state.The donated electron pairs by five Cl atoms are filled and make . The resultant shape is trigonal bipyramidal and the five  hybrid orbitals are directed towards the five corners. The five P-Cl sigma bonds, three lies in one plane and...

4.37     Write the significance of a plus and a minus sign shown in representing the orbitals.

Wave functions can be used to represent molecular orbitals. The plus and minus represent the positive wave function while negative wave function respectively.

4.36     Compare the relative stability of the following species and indicate their magnetic properties;

$O_{2},O^{+}_{2},O^{-}_{2}-(superoxide),\ O_{2}^{2-} (peroxide)$

The electronic configuration of  molecule can be written as: Here the number of bonding electrons is  and the number of antibonding electrons is . Therefore,  The electronic configuration of  molecule can be written as: Here the number of bonding electrons is  and the number of antibonding electrons is . Therefore,  The electronic configuration of  molecule can be written as: Here the...

4.35     Use molecular orbital theory to explain why the $Be_{2}$ molecule does not exist.

The electronic configuration of Be is  . From the molecular orbital electronic configuration, we have for  molecule, We can calculate the bond order for  is  where,  is the number of electrons in bonding orbitals and  is the number of electrons in anti-bonding orbitals. So, therefore we have, Bond order of  that means that the molecule is unstable. Hence, molecule does not exist.

4.34     Write the important conditions required for the linear combination of atomic orbitals to form molecular orbitals.

The important conditions required for the linear combination of atomic orbitals to form molecular orbitals are as follows: 1. The combining atomic orbitals must have the same or nearly the same energy. 2..The combining atomic orbitals must have the same symmetry about the molecular axis. 3. The combining atomic orbitals must overlap to the maximum extent.

4.33     Explain the formation of  $H_{2}$  molecule on the basis of valence bond theory.

Formation of  molecule: Assume that two hydrogen atoms with nuclei  and electrons are taken to undergo a reaction to form a hydrogen molecule. When the two atoms are at a large distance, there is no interaction between them. As they approach each other, the attractive and repulsive forces start operating. Attractive force arises between: (a) The nucleus of one atom and its own electron i.e.,...

4.32     Distinguish between a sigma and a pi bond.

Difference between the sigma bond and the pi bond is shown in the table below: Sigma  Bond Pi  Bond (a) Formed by end to end overlapping of orbitals. Formed by the lateral overlapping of orbitals (b) Sigma bonds are stronger than the pi bond. Weak bond. (c) The orbitals involved in the overlapping are s-s, s-p, p-p. Bonds are formed only with overlapping of p-p orbitals. (d) The...

4.31     What do you understand by bond pairs and lone pairs of electrons?  Illustrate by giving one exmaple of each type.

The shared pairs of electrons present between the bonded atoms are called bond pairs. And all valence electrons may not participate in bonding that electron pairs that do not participate in bonding are called lone pairs of electrons. For examples, In  ethane, there are seven bond pairs but no lone pair is present. In , there are two bond pairs and two lone pairs on the central atom (oxygen).

4.30     Which hybrid orbitals are used by carbon atoms in the following molecules?

(e)  $CH_{3}COOH$

is making 4 sigma bonds (single bond) therefore it is  hybridised. and  is making a 2 sigma bonds with carbon and 1 sigma bond with oxygen and one pi bond with oxygen therefore it is   hybridised.

4.30     Which hybrid orbitals are used by carbon atoms in the following molecules?

(d) $CH_{3}-CHO$

is making 4 sigma bonds (single bond) therefore it is  hybridised. and  is making a 3 sigma bonds with hydrogen, carbon and oxygen. and one pi bond with oxygen therefore it is   hybridised.

4.30     Which hybrid orbitals are used by carbon atoms in the following molecules?

(c)  $CH_{3}-CH_{2}-OH$

is making 4 sigma bonds (single bond) therefore it is  hybridised. and  is also making a 4 sigma bonds. therefore it is also   hybridised. Therefore they both are  hybridized.

4.30     Which hybrid orbitals are used by carbon atoms in the following molecules?

(b)  $CH_{3}-CH=CH_{2};$

is making 4 sigma bonds (single bond) therefore it is  hybridised. While  are making a double bond.  Therefore they both are  hybridized.

4.30     Which hybrid orbitals are used by carbon atoms in the following molecules?

(a) $\inline CH_{3}-CH_{3}$

There are 4 sigma bonds (single bond) each with the help of one s hybrid orbital and 3 p hybrid orbital, Hence C1 and C2 are  hybridized.

4.29     Considering x-axis as the internuclear axis which out of the following will not form a sigma bond and why?

(d) $1s \; and \; 2s.$

Orbitals   will form a sigma bond as both 1s and 2s orbitals are spherical and can combine along the x-axis as the internuclear axis.

4.29     Considering x-axis as the internuclear axis which out of the following will not form a sigma bond and why?

(c)  $2p_{y}\; and\; 2p_{y}$

Orbitals   will not form a sigma bond as both 2py orbital are align in y -direction but the internuclear axis is x-axis.  Formation of pi bond takes place.

4.29     Considering x-axis as the internuclear axis which out of the following will not form a sigma bond and why?

(b) $1s \; and\; 2p_{x}$

Orbitals   will form a sigma bond as 1s orbital and 2px orbital are align such that they can combine along x-axis as the internuclear axis.

4.29     Considering x-axis as the internuclear axis which out of the following will not  form a sigma bond and why?

(a) $1s \; and\; 1s$

Orbitals   will form a sigma bond as both orbitals are spherical and can combine along x-axis as the internuclear axis.

4.28     What is the total number of sigma and pi bonds in the following molecules?

(b)  $C_{2}H_{4}$

Given molecule : So, there are five sigma (4C-H bonds + 1 C-C bond) and one pi-bonds (C-C bonds) in .
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