CBSE Class 11th Chemistry Notes for Chapter 11 The P-Block Elements

                UNIT 11 THE p-BLOCK ELEMENTS

 

GROUP 13 ELEMENTS: THE BORON FAMILY

Elements: Boron, Aluminium, Gallium, Indium, Thallium

Electronic configuration: The outer electronic configuration of these elements is ns² np¹.

Atomic radii: Atomic radii increase on going down the group.

Ionization enthalpies: The ionization enthalpies do not decrease smoothly down the group.

Electronegativity: Down the group, electronegativity first decreases from B to Al and then increases marginally.

Physical properties:

• Boron is non-metallic in nature. It is extremely hard and black coloured solid. It has an unusually high melting point.
• Rest of the members are soft metals with low melting point and high electrical conductivity.
• Density of the elements increases down the group from boron to thallium.

Chemical properties:

• Reactivity towards air: With oxygen, these elements form their respective oxides. With dinitrogen, they from nitrides.
• Reactivity towards acids and alkalis: Boron does not react with acids and alkalis but aluminium dissolves in mineral acids and aqueous alkalis.
• Reactivity towards halogens: These elements react with halogens to form trihalides.

 

GROUP 14 ELEMENTS: THE CARBON FAMILY

Elements: Carbon, Silicon, Germanium, Tin, Lead

Electronic configuration: The valence shell electronic configuration of these elements is ns² np².

Covalent radius: There is a considerable increase in covalent radius from C to Si. From Si to Pb, there is a small increase in radius.

Ionization enthalpy: The first ionization enthalpy of group 14 members is higher than the corresponding members of group 13.

Electronegativity: The elements of this group are slightly more electronegative than group 13 elements.

Physical properties:

• All the elements of this group are solid.
• Melting points and boiling points of group 14 elements are much higher than those of corresponding elements of group 13.

Chemical properties:

• Reactivity towards oxygen: All members when heated with oxygen form oxides.
• Reactivity towards water: Carbon, silicon, germanium and lead are unaffected by water but tin forms its dioxide and dihydrogen gas.
• Reactivity towards halogen: They form halides with halogens.