Page 1 - Microsoft Word - P-BLOCK ELEMENTS LN-1

CHEMISTRY

(CHAPTER-THE P-BLOCK ELEMENTS)

SUBTOPIC - GR.13 ELEMENTS ( BORON FAMILY )TRENDS IN

ATOMIC PROPERTIES, PHYSICAL PROPERTIES, CHEMICAL
PROPERTIES, SOME IMPORTANT COMPOUNDS OF BORON, USES OF

BORON AND ALUMINIUM AND THEIR COMPOUNDS

KEY NOTES:

• TRENDS IN ATOMIC PROPERTIES

 Group 13 elements are B, Al, Ga, In,Tl
 The outer electronic configuration of these elements is ns2np1.
 Boron and aluminium have noble gas core, gallium and indium

have noble gas plus 10 d-electrons, and thallium has noble gas

plus 14 f- electrons plus 10 d-electron cores.
 Atomic radius of Ga is less than that of Al. This is due to
variation in the inner core of the electronic configuration. The

additional 10 d-electrons offer only poor screening effect for
the outerelectrons from the increased nuclear charge in

gallium.
 The observed discontinuity in the ionisation enthalpy values

between Al and Ga, andbetween In and Tl are due to inability of
d- and f-electron which have low screening effect, to

compensate the increase in nuclear charge.
 Down the group, electronegativity first decreases from B to Al

and then increases.
 TRENDS IN PHYSICAL PROPERTIES

• Boron is non-metallic in nature. Metallic character increases
down the group.

• The m.p decreases from B to Ga and then increase onwards.
Due to very strong crystalline lattice, boron has unusually high

melting point. Ga has extremely low m.p due to decrease in
magnitude of close packing.