Boron Family Elements in the Periodic Table

The group-13 elements present in the modern periodic table are much better known as the members of the Boron family. The members of the boron family exhibit a wide range of both physical and chemical properties. The electronic configuration of the elements of the boron family can be given by ns2 np1.

The members of this family include Boron (B), Gallium(Ga), Aluminium (Al), Thallium (Tl), Indium (In) and including a radioactive synthetic element, Nihonium (Nh), which was formerly known as ununtrium.

Properties of Boron Family

The chemical and physical properties of the boron family members are found to follow a specific trend. Also, the properties of boron vary from the other members of the group because of the absence of the d orbital and its smaller size. These deviations in the boron properties lead to the classification of boron’s anomalous properties.

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Trends in Properties of Members of the Boron Family

Let us look at the trends in properties of the boron family members listed as follows:

• The boron family members react with halogens to produce bromides, iodides, and tri-chlorides. All these halides are covalent in nature and hydrolyzed in water.

• The compounds of these elements, such as octahedral [M(H2O)6]3+ (where M denotes a member of the boron family) and tetrahedral [M(OH)4]–, exists in an aqueous medium.

• These trihalides are strong Lewis acids due to the deficiency of electrons.

• The metallic character of the boron increases down the group while we move from boron to thallium.

• First, the electronegativity of the elements decreases down the group from B to Al and, after that, increases marginally due to the discrepancies existing in the atomic size of the elements.

Anomalous Properties of Boron

Because of the unavailability of d-electrons and their smaller size, boron is found to exhibit properties that are in contrast to the other elements associated with the boron family. These properties are referred to as anomalous properties of boron. A few of these anomalous properties can be listed as follows:

• Except for boron, the compounds of the elements of the boron family such as octahedral [M(H2O)6]3+ (where M denotes the member of boron family), and tetrahedral [M(OH)4]– exists in an aqueous medium.

• Due to the absence of d orbitals, the maximum covalency of boron is 4.

• While the rest of the family are post-transition metals, boron is given as a metalloid.

• Hydroxides and boron oxides are of an acidic nature, while, on the other hand, the other elements in the boron family form hydroxides and oxides of an amphoteric nature.

Characteristics of Boron Family

The boron group is notable for its trends in the electron configuration and a few of its characteristics of the elements. Boron varies from the other group members in its refractivity, reluctance, and hardness to participate in metallic bonding. One of the examples of a trend in reactivity is given as the tendency of boron to form reactive compounds with hydrogen.

While located in the p-block, the party is notorious for the octet violation rule of boron and (to a lesser extent) aluminium by its members. These elements can place only six electrons (in 3 molecular orbitals) onto the valence shell. All the members of this group are characterized as trivalent.

Chemical Reactivity

Hydrides

Most of the elements found in the boron group show increasing reactivity as the elements get heavier in the atomic mass and higher in the atomic number. Boron, which is the first element in the group, is normally unreactive with several elements except at high temperatures, though it is capable of producing several compounds with hydrogen, at times called boranes. The simplest borane is either B₂H₆ or diborane. B₁₀H₁₄ is another example.

Oxides

All the boron-group elements are much known to produce a trivalent oxide, involving two atoms of the element, which is covalently bonded with three oxygen atoms. These elements exhibit an increasing pH trend (from acidic to basic).

Toxicity

All the elements in the boron group can be said to be toxic, given a high enough dose. A few of them are only toxic to animals, some only to plants, and a few to both.

An example of boron toxicity: It has been noticed to harm barley in concentrations exceeding 20 mm. The boron toxicity symptoms are numerous in plants. As per the research, they include decreased shoot and root growth, reduced cell division, inhibition of photosynthesis, decreased production of leaf chlorophyll, reduced proton extrusion from roots, lowering of stomata conductance, and the deposition of suborgin and lignin.

Aluminium does not give a prominent toxicity hazard in smaller quantities, but it is slightly toxic in very large doses. Gallium is not considered to be toxic, although it may contain some minor effects. Indium is not toxic and can be handled with approximately similar precautions as gallium, but a few of its compounds are slightly to moderately toxic.