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The p-Block Elements

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Chemistry I

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Class 10 Class 12
NO is paramagnetic in the gaseous state but diamagnetic in the solid and liquid states. Justify?

NO has odd number of electrons (7 + 8 = 15) and due to the presence of unpaired electron, it is paramagnetic in the gaseous state.

However, in the liquid and solid states, the unpaired electrons are involved in the formation of loose dimer. In the absence of any unpaired electrons, it is diamagnetic in nature.

Which one of the following does not exist?
  • XeOF4
  • NeF2 
  • XeF2
  • XeF6



List the uses of neon and argon gases.

neon and argon is inert gas because they are more stable than other.

Uses of Neon:
(i) Neon is mainly used in fluorescent lamps of tubes for advertising purposes. These are known as neon signs and can be seen at long distances even when there is a fog. Neon actually produces an orange red glow in the tube and on mixing with the vapours of other gases, glows or signs of different colours can be obtained.

(ii) It is used in filling sodium vapour lamps.

(iii) It is used in safety devices for protecting certain electrical instruments (voltmeters, relays, rectifiers etc.)

Uses of Argon:
(i) It is used in metal filament electric lamps since it increases the life of the tungsten filament by retarding its vapourisation.

(ii) A mixture of argon and mercury vapours is used in fluorescent tubes.

(iii) It is used to create an inert atmosphere for welding and for carrying certain chemical reactions.


Discuss the general characteristics of Group 15 elements with reference to their electronic configuration, oxidation state, atomic size, ionization enthalpy and electronegativity.

(i) Electronic configuration: The valence shell electronic configuration of these elements is ns2 np3. The s orbital in these elements is completely filled and p orbitals are half filled, making their electronic configuration extra stable.

(ii) Atomic Size: Covalent and ionic (in a particular state) radii increase in size down the group. There is a considerable increase in covalent radius from N to P. However, from As to Bi only a small increase in covalent radius is observed. This is due to the presence of completely filled d and f or f orbitals in heavier members

(iii)Oxidation State: The common oxidation states of these elements are –3, + 3 and + 5. The tendency to exhibit –3 oxidation state decreases down the group due to increase in size and metallic group. In the last member of the group, bismuth hardly forms any compound in –3 oxidation state. The stability of + 5 oxidation state decreases down the group. The stability of + 5 oxidation state decreases and that of + 3 state increases (due to invert pair effect) down the group. Nitrogen exhibits + 1, + 2, + 4 oxidation states also when it reacts with oxygen. Phosphorus also shows +1 and + 4 oxidation states in some oxo acids.

(iv) Ionization enthalpy: Ionization enthalpy decreases down the group due to gradual increase in atomic size. Because of the extra stable half filled p orbitals electronic configuration and smaller size, the ionization enthalpy of the group 15 elements is much greater than that of group 14 elements in the corresponding periods. The order of successive ionization emthalpies are expected as ΔH1, < ΔH2 < ΔH3.

(v) Electronegativity: The electronegativity value, in general, decreases down the group with increasing atomic size. However, amongst the heavier elements, the different is not that much pronounced.


Write main differences between the properties of white phosphorus and red phosphorus. 


White Phosphorus

Red phosphorus

1. Colour

White but turns

Dark red


yellow on exposure


2. State

Waxy solid

Brittle powder

3. Density

1.84 g cm-3

2.1 gcm3

4. Ignition

307 K

543 K



5. Stability

Less stable at ordi-

More stable at ordi –


nary temperature.

nary temperature

6. Chemical

Very reactive

Less reactive



Justify the placement of O, S, Se, Te and Po in the same group of the periodic table in terms of electronic configuraton, oxidation state and hydride formation. 

(i) Electronic configuration: They all have six electrons in the outermost shell and have ns2 np4 general electronic configuration.
(ii) Oxidation state: The outer configuration of all these elements is ns2 np4. Therefore, they complete their octet either by gaining two electrons or by sharing two electrons. Two types of oxidation states are shown by these elements.
(a) Negative oxidation state: Except the compound OF2 oxygen shows-2 oxidation state in all its compounds. Due to hgh electronegativity, it forms O2' ion in most of the metal oxides.
The electronegativities of S, Se, Te are low hence their compounds even with most electropositive elements are not more than 50% ionic. Hence S2–', Se2–' and Te2–' are less probable. Being a metal Po does not form Po2+ ion at all.
(b) Positive oxidation state: Oxygen does not show positive oxidation state except OF2(O = + 2). With the increase in atomic number of electro negativity is decreasd in this group, hence the tendency to show the positive oxidation states will increase. S, Se, Te, Po show + 4, +6 oxidation state in addition to + 2.
(iii) Hydride formation: All the elements O, S, Se, Te and Po form M2M type hydrides (where M = O, S, Se, Te and Po)