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Summary Neet prep : the p-BLOCK ELEMENTS

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  • Course
  • NEET
  • Institution
  • NEET
  • Book
  • Chemistry Part II (NCERT XII)

The p-BLOCK ELEMENTS includes description of all elements in the p-BLOCK from group 1 -boron family to noble gas family including trends and exception in trends that is almost enough for neet 2025 preparation.

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  • No
  • P block
  • July 27, 2024
  • 30
  • 2023/2024
  • Summary

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  • the p block elements

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1




THE p-BLOCK ELEMENTS


GROUP 13 ELEMENTS: (ns² np¹)




Indroduction :


● Only boron forms [BF4]-¹ ion, while aluminium can form [AlF6]-³ ion due to availability of

empty 3d orbital.

● First members of all p-BLOCK elements forms pπ - pπ bond due to influences of

combined effect of size and unavailability of d - orbital , while heavier elements can

form dπ - dπ (or) dπ - pπ bonds .

● The co-ordination number of the heavier species elements also higher than for the first

elements due to the contribution of the d- orbital for the π bond .

● Boror family contains

a. Boron 5

b. Aluminium 13

c. Galium 31

d. Indium 49

e. Thallium 81

f. Nihonium 113

■ (mass no: 286 gmol-¹,

■ half life - 20second)

, P- block elements 2


● Abundance


Elements Percentage of abundance Rank

Oxygen 45.5% I

Silicon 27.7% II

Aluminium 8.3% III


Atomic radii:


● Atomic radii increases down the group.

● Exception: Atomic radii of gallium (135pm) is lesser than aluminium (143 pm ) due to poor

shielding effect of 3d orbital.



Ionization enthalpy :


● Decreases down the group

● Some discontinuity in the ionisation enthalpy values between Al and Ga and between In

and Tl are due to inability of d and f- orbital which has poor screening effect to

compensate the increase in the nuclear charge .

B > Tl > Ga > Al > In



Electronegativity:


● Down the group, electronegativity first decreases fron B to Al and then increases

marginally

B > Al ≤ Ga ≤ In ≤ Tl



Physical properties:


● Boron is non metallic , hard and black coloured solid and has high melting point due to

very strong crystalline lattice .

, P- block elements 3


● Other members are soft metal with low melting point and high electrical electrical

conductivity .

● Gallium with low melting point (303K ) can exist in liquid during summer and it's high

boiling point (2676K) makes it useful for measuring high temperature

● Density of elements increase down the group from boron to thallium.



Chemical properties :


● +1 oxidation as expected from the energy considerationa were more ionic than those in

+3 oxidation .

● BCl3. NH3 can be easily formed because of the electron deficienct (Lewis acid)

tendency of boron.

● AlCl3 achieves stability by forming a dimer.




●

● Trivalent state of the most of the compounds being covalent are hydrolysed in water

● Hydrolysis of trichlorides in water form tetrahedral with sp³ hybridization [M(OH)4]-.

● Hydrolysis of Aluminium trichlorides in acidified aqueous solution form octahedral

[Al(OH)6]+³ ion. (Due to 3d orbital)



Reactivity towards air :


● Crystalline boron is unreactive .

, P- block elements 4


● Amorphous boron and aluminium metal on heating the air form their respective oxide and

at high temperature form their respective nitrides .

● Aluminium forms a thin oxide layer on the surface which protects the metal from

further attack..


Oxides Nature of oxide

B2O3 Acidic

AL2O3 Amphoteric

Ga2O3 Amphoteric

In2O3 Basic

Tl2O3 Basic



● Boron trioxide reacts with basic mettalic oxide like alkali metal oxide . But Boron does

not react with acid or alkali.



Reactivity towards acids and base :


● Aluminium dissolves in dilute HCl and liberates dihydrogen.

2Al(s) + 6HCl(aq) —» 2Al+³(aq) + 6Cl-¹(aq) + 3H2 (g)

● Concentrated nitric acid is rendered passive by forming a protective oxide layer on the

surface.

● Aluminium reacts with aqueous alkali and liberate dihydrogen.

2Al(s) + 2NaOH (aq) + 6H20 (l) —» 2Na +[Al(OH)4]- (aq) + 3 H2 (g)



Reactivity towards halogens :



● These elements react with halogens to form trihalide except TlI3

, P- block elements 5


● White fume appear around the bottle of anhydrous aluminium chloride due to the partial

hydrolysis of anhydrous aluminium chloride with the atmospheric moisture to liberate

HCl gas . Moist HCl appears white in colour .



Important trend and Anomalous properties of Boron :


● Trichlorides, tribromides , Tri-iodides of All Elements are covalent in nature and are

easily hydrolysed in water .

● Species like octahedral [M(OH)6]+³ and Tetrahedral [M(OH)4]-, exist in aqueous medium

except in boron .




Group 14 Elements : The Carbon Family (ns²np²)




Indroduction :

● Carbon is the seventeenth most abundant element by mass and most versatile element in

the world .

● C¹⁴ has half life period of 5770 years.

● Tin occurs mainly as cassiterite .

● SnO2 and lead is obtained as Galena.

● Ultrapure form of germanium and silicon are used to make transistor and semiconductor.

● The carbon family including:

a. Carbon 6

b. Silicon 14

c. Germanium 32

d. Tin 50

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