The p-Block Elements

p-Block Elements: p block elements notes class 12 download from below link:

Elements in which the last electron enters any one of the three p-orbitals of their respective outermost shell are called p-block elements.

Group 15 elements

Group 15 elements are collectively called pnictogens.

Chemical properties:

Stability of +3 oxidation state increases and that of +5 decreases down the group due to inert pair effect.

Halides: All the elements form trihalides of the type MX3 and except nitrogen, all form pentahalides of the type MX5.

– Stability: NF3 > NCl3 > NBr3

– Lewis acid strength: PCl3 > AsCl3 > SbCl3 and PF3 > PBr3 > PI3

– Lewis base strength: NI3 > NBr3 > NCl3 > NF3

– Bond angle: PF3 < PCl3 < PBr3 < PI3

(increasing b.p. – b.p. repulsions)

Hydrides: All the elements form hydrides of the type MH3 which are covalent and pyramidal in shape.

Oxides: All these elements form oxides of the type X2O3, X2O4 and X2O5

GROUP 16 ELEMENTS (OXYGEN FAMILY)

Group 16 elements are collectively called chalcogens.

Chemical properties:

The stability of –2 oxidation state decreases down the group, the stability of +4 oxidation state increases and that of +6 oxidation state decreases down the group due to inert pair effect.

Hydrides: All the elements form stable hydrides of the type H2M. Their general trends are:

Halides: All elements form halides of the type EX6, EX4 and EX2.

Properties:

– Dioxygen is colourless and odourless gas, soluble in water and paramagnetic in nature.

– Dioxygen directly reacts with all metals (except noble metals like Au, Pt ), non-metals (except noble gases).

Uses:

– For arti_cial respiration in hospitals and by mountaineers, pilots and divers.

– In oxy-hydrogen and oxy-acetylene torches which are used for cutting and welding of metals.

– Liquid dioxygen is used as rocket fuel.

GROUP 17 ELEMENTS (HALOGEN FAMILY)

Group 17 elements are collectively called halogens.

Chemical properties:

F shows only – 1 oxidation state while other elements show –1, +1, +3, +5 and +7 oxidation states also.

General trends:

– Reactivity: F2 > Cl2 > Br2 > I2

– Boiling points: HF > HI > HBr > HCl

– Melting points: HI > HF > HBr > HCl

– Bond lengths: HI > HBr > HCl > HF

– Bond dissociation enthalpy: HF > HCl > HBr > HI

– Acidic strength: HI > HBr > HCl > HF

– Thermal stability: HF > HCl > HBr > HI

– Reducing power: HI > HBr > HCl > HF

Oxides:

– Fluorine forms two oxides OF2 and O2F2 called oxygen fluorides, other halogens form oxides in which oxidation states of these halogens range from +1 to +7.

– The higher oxides of halogens are more stable than the lower ones. The p-Block Elements 125

Metal halides:

– Ionic character: MF > MCl > MBr > MI

– For metals exhibiting more than one oxidation states, the halides in higher oxidation states will be more covalent than the one in lower oxidation states.

Properties: It is a yellowish-green gas, poisonous in nature, soluble in water. Its aqueous solution is known as chlorine water.

Uses: It is used as a bleaching agent, disinfectant and in the manufacture of CHCl3, CCl4, DDT, bleaching powder, poisonous gas phosgene (COCl2), tear gas (CCl3NO2) and mustard gas (ClC2H4SC2H4Cl).

GROUP 18 ELEMENTS (NOBLE GASES)

These are monoatomic gases and are also known as rare gases or aerogens.

Chemical properties: Noble gases are the least reactive due to high ionization enthalpy and more positive electron gain enthalpy.