Question 1

Among III-A group elements, the elements with highest and lowest I.P. values are:

Accepted Answer

I.P.  does not smoothly decrease down in  III-A  group. The decrease from B to Al is associated with increase in size. The observed discontinuity in the  I.P.  values between  Al  and  Ga , and between  In  and  Tl  are due to the inability of d- and f-electrons, which have low screening effect to compensate the increase in nuclear charge.

Question 2

In representative elements the ionization energy values generally decrease smoothly down the group. But in boron group the values show an erratic trend. This is mainly due to :

Accepted Answer

Poor shielding of nuclear charge in Ga by 3d electrons results in smaller atomic size and higher I.P for the atom. Similarly, in TI the poor shielding by the 4f electrons leads to higher I.P or the atom. Hence, first I.P values for the 3rd group elements show erratic trend.

Question 3

Which of the following correctly represents the variation of electronegativity (EN) with atomic number (Z) of group 13 elements?

Accepted Answer

The electronegativity of group 13 elements decreases from B to Al and then increases from Al to Tl. This is because of the discrepancies in the atomic size of the elements.

Question 4

Assertion (A): Among IIIA group elements boron has highest melting pointReason (R) : Boron exists as a giant covalent polymer :

Accepted Answer

Due to very strong crystalline lattice, boron has unusually high melting point.

Question 5

Find out the similarities between  I_2Cl_6  and  Al_2Cl_6 .

Accepted Answer

A)  Both   I_2Cl_6  and   Al_2Cl_6  have   3C\, -\, 4e^-  bonds. Hence, option A is correct.B) In   I_2Cl_6 , the central  I  atom undergoes  sp^3d^2  hybridization and in   Al_2Cl_6 , the central  Al  atom undergoes  sp^3  hybridization. Thus, the option B is incorrect.C)   I_2Cl_6  is planar and   Al_2Cl_6  is non planar. Thus, the option C is incorrect.

Question 6

Compare x, y, z bond angle from the above given molecules:

Accepted Answer

The bond angles are as given below. x\, =\, 94^{\circ} ;  y\, =\, 84^{\circ} ;  z\, =\, 91^{\circ} Thus, the correct order of bond angles is  x > z > y .Terminal chlorine has three lone pairs so repulsion is more between two terminal chlorine, but bridging chlorine has two lone pairs so repulsion between one terminal and one bridging chlorine is less than the terminal chlorine. Higher repulsion results in higher bond angle.

Question 7

Aluminium exhibits +3 oxidation state. As we move down the group, +1 oxidation states get more stable. This is a consequence of :

Accepted Answer

Answer:- (B) inert pair effectThe atoms of group 13 elements have 3 valence electrons, two in s-subshell and one in p subshell.The +1 oxidation state becomes more stable as we move down to the group due to inert pair effect. After the removal of 1 electron from p orbital, the remaining  ns^2  electrons behave like stable noble gases due to inert pair effect and do not take part in compound formation. The two electrons present in the s-shell are strongly attracted by the nucleus and do not participate in bonding. This inert pair effect becomes more and more prominent on moving down the group. Hence, the +1 oxidation state gets more stable as we move down the group.

Question 8

Which of the following oxidation states are the most characteristic for lead and tin respectively:

Accepted Answer

Lead and tin are in the fourth group of the periodic table,so we can expect an oxidation state of  +4  for both of them.But due to the reluctance of participation of electrons in the outermost  s  orbital in bonding i.e., inert pair effect which increases down the group.So, the oxidation states of lead and tin are  +2  and  +4  respectively which is also evident from their respective chemical reactions.

Question 9

Which of the following element does not show inert pair effect?

Accepted Answer

The inert pair effect is the tendency of the electrons in the outermost atomic s orbital to remain unionized or unshared in compounds of post-transition metals. The term inert pair effect is often used in relation to the increasing stability of oxidation states that are two less than the group valency for the heavier elements of groups 13, 14, 15 and 16. The inert pair effect is shown by Tl, Pb and Bi due to which, the lower oxidation state is more stable than the higher oxidation state. But C, being higher up in the periodic table, does not show inert pair effect.

Some P-Block Elements