Account for the following :
The acidic strength decreases in the order `HCl gt H_2S gt PH_3`
(ii) Tendency to form pentahalides decreases down the group 15 of the periodic table.
(iii) Noble gases have large positive values of electron gain enthalpy.

(a)Account for the following : (i)The acidic strength decreases in the order HCl gt H_(2)S gt PH_(3) (ii)Tendency to form pentahalides decreases down the group in group 15 of the periodic table. (b)Complete the following chemical equations. : (i) P_(4)+SO_(2)Cl_(2)to (ii) XeF_(2)+H_(2)O to (iii) I_(2)+underset(("conc"))(HNO_(3)) to

(a) Complete the following chemical reaction equations : (i) P_(4)+SO_(2)Cl_(2) rightarrow (ii) XeF_(4)+ H_(2)O rightarrow (b) Explain the following observations giving appropriate reasons : (i) The stability of + 5 oxidation state decreases down the group in group 15 of the periodic table. (ii) Solid phosphorus pentachloride behaves as an ionic compound. (iii) Halogens are strong oxidizing agents.

In which of the following options order of arrangement does not agree with the variatioin of property indicated against it? Thinking process. i) The ionic size increases as the positive charge on the cation decreases or the negative charge on the anion increases. ii) First ionisation enthalpy increases from left to right in the periodic table. iii) Electron gain enthalpy increases as the electronegativity of the atom increases. iv) The metallic character increases as the size of the metal atom increases.

Arrange the following groups in their decreasing order of -I effect. I. NO_(2) II. SO_(3)H III. F IV. NH_(2) The correct choice is :

(b) How would you strength account for the following situations? (i) The acidic strengths of these compound increase in the following order: PH_(3)ltH_(2)SltHCI (ii)The oxidisting power of oxoacids of chlorine follows the order : HCIO_(4)ltHCIO_(3)ltHCIO_(2)ltHCIO (iii) In vapour state sulphur exhibits paramagnetic behaviou.

(a) Electropositive nature of the element(s) increases down the group and decreases across the period (b) Electronegativity of the element decreases down the group and increases across the period (c) Atomic size increase down the group and decreases across a period (left to right) (d) Metallic character increases down the group and decreases across a period On the basis of the above trends of the periodic table, answer the following about the electron with atomic number 3 to 9 (a) Name the most electropositive element among them (b) Name the most electronegative element (c) Name of the element with smallest atomic size (d) Name the element which is a metalloid (e) Name the element which shows maximum valency.

The periodicity is related to the electronic configuration. That is, all chemical and phyical properties are a manifestation of the electronic configurfation of the elements. The atomic and ionic radii generally decrease in a preiod from left or right. As a consequence , the ionisation enthalpies generally increase and electron gain enthalpies become more negative across a period. In other words, the ionisation enthalpy of the extreme left element in a period is the least and the electron left element on the extreme right is the highest negative. This results into high chemical reactivity at two extgremes and the lowest in the centre. Similarly down the group, the increase in atomic and ionic radii result in gradual decrease (with excetption in some third period elements) in electron gain enthalpies in the case of main group elements . These properties can be related with the (i) reducing and oxidising behacviour of the elements (ii) metallic and no-metallic charcter of element (iii) acidic, basic , amphoteric and neutral character of the oxides of the elements. Among Al_(2)O_(3), SiO_(2),P_(2)O_(3) and SO_(2) the correct order of acid strenght is :

(a) Draw the structures of the following : (i) XeF_(4) (ii) H_(2)S_(2)O_(7) (iii) SO_(3)^(2-) (b) Explain the following observations : (i) Phosphorous has a greater tendency for catenation than nitrogen. (ii) The negative value of electron gain enthalpy is less for fluorine than that for chlorine. (iii) Hydrogen fluoride has a much higher boiling point than hydrogen chloride.

Metals have few electrons in their valence shell while non-metals generally have more electrons in their valence shell. Metallic character is closely related to atomic radius and ionisation enthalpy. Metallic character increases from top to bottom in a group and decreases from let to right in a period of periodic table. metallic character is inversely related to electronegativity of element. Q. The electronegativity of the following elements increase in the order:

(a) (i) Complete the following chemical equations : (i) NaOH_((aq))+Cl_(2(g)) rightarrow (Hot and conc.) (ii) Xef_(6)(s)+H_(2)O(l) rightarrow (b) How would you account for the following ? (i) The value of electron gain enthalpy with negative sign for sulphur is higher than that for oxygen. (ii) NF_(3) is an exothermic compound but NCl_(3) is endothermic compound. (iii) ClF_(3) molecule has a T-shaped structure and not a trigonal planar one.