Chemistry ATOMIC, PHYSICAL AND CHEMICAL PROPERTIES
Please Wait... While Loading Full Video

ATOMIC, PHYSICAL AND CHEMICAL PROPERTIES

Atomic and Physical Properties :

(i) Atomic and Ionic radii

Atomic radii : `B > Ga < Al < In < Tl`

(ii) Ionization Enthalpies

`B > Tl > Ga > Al > In` (Sum of three IE values)

(iii) Melting and Boiling Points

M.P. `B> Al > Tl > In > Ga`

B.P. `B> Al > Ga > In > Tl`

(iv) Electropositive Character

Due to high IE they are less electropositive. On moving down the group metallic character increases due to decrease in IE [`:. B` is nonmetal and other elements are metals.]

`(B <)/text(Non metal )` `text(Al < Ga < In < Tl)/text(Metals)`

Note : Boron exists in many allotropic forms. All the allotropes have basic building `B_(12)` icosahedral units made up of polyhedron having `20` faces and `12` corners. For example one is the simplest form : `alpha`-rhombohedral boron.

But `Al`, `In` & `Tl` all have close packed metal structure.

Chemical Properties :

(i) Reaction with oxygen

`4B + 3O_2 rightarrow 2B_2O_3`

`4Al + 3O_2 rightarrow2Al_2O_3`

`Al` should react air to form a very thin oxide film (`10^(-4)` to `10^(-6)` mm thick) on the surface and protects the metal from further attack.

`2Al(s) + 3/2O_2(g) rightarrowAl_2O_3(s)`

(ii) Reaction with water

`B+H_2O text(cold & hot) rightarrow text( no reaction)`

`undersettext(red hot)(2B) +3H_2O rightarrow B_2O_3+H_2`

`Al + 3H_2O rightarrow Al(OH)_3 + 3/2H_2`

`Ga` and `In` are attacked neither by cold water nor hot water unless oxygen is present. `Tl` form an oxide on surface.

(iii) `B+HCl rightarrow text( no reaction)`

`B + H_2SO_4(text(dil)) rightarrow text( no reaction)`

`2B + 3H_2SO_4(text(conc.)) rightarrow 2H_3BO_3+3SO_2`

`B+3HNO_3 rightarrow H_3BO_3+3NO_2`

`2Al +(text(cone))6H_2SO_4 rightarrowAl_2(SO_4)_3+3SO_2+6H_2O`

`Al +(text(conc.))HNO_3(80%) rightarrow Al_2O_3(text(passive layer)) text(and does not react further.)`

(iv) `2B + 2NaOH + 2H_2O rightarrow 2NaBO_2 + 3H_2`

`2Al + 2NaOH + 2H_2O rightarrow 2NaAlO_2 + 3H_2`

(v) `2B + N_2 rightarrow 2BN, 2Al + N_2rightarrow 2AlN`

`4B + C rightarrow B_4C, 4Al+N_2 rightarrow Al_4C_3`

(vi) `3Mg + 2B rightarrow Mg_3B_2`
 
SiteLock