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Boron Family (Group 13)

  • Group 13 or III A of  the periodic table consists of five elements

  • All these elements have three electrons in the outermost orbit.

  • The electronic configuration of the outermost energy levels of these elements may be represented as ns2np1 .

General Characteristics of Group 13 elements:

Physical Properties

Atomic and ionic radius :

  • The atom, radius increases from boron to thallium. The abrupt increase in the atomic radius of Al is due to greater screening effect in AI (it has 8 electrons in the penultimate shell) than in B (it has 2 electrons in the penultimate shell).

  • Further, there is not much increase at gallium and thallium due to the intervening d and f electrons which do not screen the nuclear charge effectively.

  • The ionic radii (M3+) increase from boron to thallium.


  • Density increases from B to Tl due to increase in size of the atom.

  • Aluminum has an extremely low density and hence used as an important structural material.

Melting and Boiling Point:

  • Melting points do not vary regularly due to structural changes in the elements.

  • Boron has a very high melting point because it exists as a giant covalent polymer in both solid and liquid states.

  • The melting point decreases from B to Ga and then increases.

  • Low m.p. of Ga (29.8°C) is due to fact that it consists of only Ga2, molecules; it remains liquid upto 2000°C and hence used in high temperature thermometry.

Ionization Energy:

  • In spite of the large nuclear charge and small size, the first ionization energies of these elements are less than the corresponding value of s-block elements.

  • This is because p- electrons are Iess penetrating and more shielded than s electrons they are farther from the nucleus and hence held less tightly than free s-electrons and thus can be easily removed.

Electropositive (metallic) character:

  • Electropositive (metallic) character increases from B to Tl. This is also indicated from the ionization energy values of these elements.

  • Boron is a semi-metal; it is closer to non-metals then to metals in properties (its crystalline form is hard, inert and poor conductor of electricity).

  • Aluminium and other elements are metallic (i.e. they are good conductor of electricity) and have more or less an equal electropositive character. This is indicated by their first ionisation energies which differ only slightly from one another.

To read more, Buy study materials of S- Block elements comprising study notes, revision notes, video lectures, previous year solved questions etc. Also browse for more study materials on Chemistry here.

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