Properties of Boron Family

The elements present in the group 13 of the modern periodic table are known as Boron family (includes B, Al, Ga, In, Tl, Uut). These elements have 3 electrons in their outermost shell. Only one member of this family i.e. boron is typically a non-metal. Rest of the other elements are metals. Properties of these elements in the group vary greatly.

Physical Properties of Boron

The first element of B family i.e., boron itself has some physical properties different from that of rest of the members. It is a hard and black coloured non-metallic solid.  The existence of boron can be seen in its many allotropic forms. It has an unusually high melting point because of the very strong crystal lattice. In contrast, the rest of the members are soft in nature and have low melting points.  They have high electrical conductivity.

Chemical Properties of Boron

Oxidation states and trends in chemical reactivity:

Boron generally forms covalent bonds rather than +3 ions. This is due to the small size of boron which makes the sum of its first three ionization enthalpies very high. While moving from B to Al, the sum of the first three enthalpies drastically decreases. This results in the formation of Al3+ ions. Aluminium is a highly electropositive element.

Moving down the group, the shielding effect decreases, this results in a higher effective nuclear charge. So the nucleus holds ns electrons tightly. Hence, only p orbital electrons are allowed for bonding. In Ga, In and Tl, oxidation states can be found as both +1 and +3. The relative stability of +1 oxidation state can be seen as follows: Al< Ga< In <Tl

Compounds in + 1 oxidation state are more ionic in comparison to +3 oxidation state.

  • Reactivity towards air: Boron is unreactive towards the air. Aluminium forms a thin layer of oxide which makes it unreactive to other substances. Amorphous boron and aluminium when reacted with air by providing heat from B2O3 and Al2O3 These elements are heated with dinitrogen to form nitrides.2 AlThe nature of the oxides varies as we move down the group. Boron trioxide is acidic in nature. Aluminium and gallium oxides are amphoteric in nature. Whereas indium and thallium are basic in nature.
  • Reactivity towards acids and alkalis: Boron is unreactive when comes in contact with acids and alkalis at moderate temperatures. Aluminium reacts with mineral acids and aqueous alkalis thus show amphoteric character.
  • The reaction of aluminium with HCl:

boron a1

  • The reaction of aluminium with aqueous alkali:

boron a2

  • Reactivity towards halogen: The boron family reacts with halogens to form trihalides (except TlI3)

boron a3                 {X= F, Cl, Br, I}

In this article, we briefly discussed the common properties of group 13 elements, Anomalous Properties of Boron. To know about the properties of other groups of elements in the periodic table, download BYJU’S – The Learning App.

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