Boron family - Anomalous Properties of Boron

The group 13 elements in the modern periodic table are better known as the members of Boron family. The members of this family exhibit a wide range of physical and chemical properties. The electronic configuration of these elements is given by ns² np¹.

The members of this family are:

Boron (B), Aluminium (Al), Gallium(Ga), Indium (In), Thallium (Tl) and a radioactive synthetic element, Nihonium (Nh) formerly known as ununtrium.

The chemical and physical properties of the members of boron family are found to follow a particular trend. Properties of boron differ from other members of the group due to its smaller size and absence of the d orbital. These deviations in properties of boron lead to the classification of anomalous properties of boron.

Table of Contents

• Trends in properties of members of boron family
• Anomalous properties of boron

Trends in properties of members of boron family:

1. The members of the boron family react with halogens to form tri-chlorides, bromides, and iodides. These halides are covalent in nature and are hydrolyzed in water.
2. The compounds of these elements like tetrahedral [M(OH)₄]^– and octahedral [M(H₂O)₆]³⁺ (where M denotes a member of the boron family), exists in an aqueous medium.
3. Because of the deficiency of electrons, these trihalides are strong Lewis acids.
4. Metallic character increases down the group as we move from boron to thallium.
5. Electronegativity of the elements first decreases down the group from B to Al and then increases marginally because of the discrepancies in the atomic size of the elements.

Anomalous properties of boron:

Due to its smaller size and unavailability of d-electrons boron is found to exhibit properties which are in contrast to the other elements of the boron family. These properties are known as anomalous properties of boron. Some of these anomalous properties are discussed below.

1. Except for boron, the compounds of the elements of the boron family like tetrahedral [M(OH)₄]^– and octahedral [M(H₂O)₆]³⁺ (where M denotes the member of boron family) exists in an aqueous medium.
2. The maximum covalence of boron is 4 due to the absence of d orbitals.
   
3. Boron is a metalloid while the rest of the family are post transition metals.
4. The boron oxides and hydroxides are acidic in nature, whereas the other elements in the family form oxides and hydroxides which are amphoteric in nature.

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