Compound of Boron and Anomalous Properties of Boron

Boron is a chemical element with the symbol B, with atomic number 5, and it comes under the 13th group. Also known as group III-A element, it is a colorless and odourless metalloid and is found in the 2nd period. The element is an important industrial material mostly used in the manufacture of ceramics and glass and proves to be beneficial in several fields. In this section, we are going to discuss the compounds formed by Boron and their anomalous behaviour.

Properties of Boron

• Boron ranks number 5 in the periodic table and is part of the 13th group
• While the rest of the members of the Boron group are metals, the boron element is non-metal
• It also displays allotropy, whereas other members do not
• The pure element boron weighs 10.811 g/mole and has a density measuring 2.37 g/cc while in an isolated state
• Physical appearance-wise, it is a solid element when at room temperature and falls under the category of semi-metal elements otherwise
• Its melting point is 2348K, whereas its boiling point is 4273K, which is the highest among all the elements of group 13

Compounds of Boron:

Boron is a fairly unreactive element, and a few boron compounds can be found in nature. These compounds have been proven to be quite useful in the production of a variety of products in different areas. Here are some of the most important boron compounds found in nature:

1. Borax

Borax is a naturally occurring boron compound that can be found all over the world. Tincal is the most common form, and it includes roughly 55 percent boron in its natural state. Tincal is abundant in India, Tibet, and portions of the United States, such as California. Borax is one of the most important compounds of Boron. Its formula is  Na₂[B₄O₅(OH₄].8H₂O, whereas the white crystalline borax with solid structure is denoted by Na₂B₄O₇.10H₂O. When you dissolve borax in water, it forms an alkaline solution. On heating, borax loses its water which leads to swelling of its molecule. This changes the structure of borax and it becomes glass-like and forms into borax beads on further heating. When borax is heated initially it results in the formation of sodium metaborate, and on further heating, it forms sodium anhydride. An important thing to know here is that you can use a borax bead test to identify the presence of transition metals, since the metaborate of transition metals differ in colors. For instance, if you heat borax on a platinum wire along with CoO, it will form a blue coloured bead.

Uses

• Borax is involved in the manufacturing of enamels and, in particular, glass. It’s also used to make cleaning products, drying oils and ceramics
• There must be a flux in welding procedures, and borax serves as a flux in such processes
• We notice that the wick of a candle is made of hard material in our daily lives. This recipe calls for the usage of borax
• Borax is also used in the production of fabric softeners and laundry detergents
• Borax can also be used as a germicide

2. Boric Acid or Orthoboric acid

Boron also produces a weak acid. There are a variety of acids that are formed based on the amount of water present. H₃BO₃, or orthoboric acid (boric acid), is one of the most important acids that may be produced. It’s a white crystalline substance that has a soapy feel to it. It is just slightly soluble in water, but it dissolves completely in hot water. Boric acid takes electrons from the hydroxyl ion and acts as a Lewis acid.

Uses:

• Boric acid, like the compound borax, it is used in the production of enamel and ceramic coatings
• It’s also used in the production of borax and other pigments. Food preservation is a really important use
• Boric acid is utilized in the food business as a preservative, as well as in the production of borosilicate glass
•  Boric acid is also used as an eyewash and is thought to be effective

3. Diboranes

(B₂H₆) is another significant boron family chemical. Boranes are compounds that only have the elements boron and hydrogen as their primary constituents. B₂H₆ is the chemical formula for diborane. We get diborane when boron trifluoride is treated with LiAlH₄ in diethyl ether. Diborane is colourless and extremely poisonous, with a boiling point of 180°C. Diborane is a very spontaneous substance in nature, thus it easily catches fire and produces a large quantity of energy. It exhibits a cleavage reaction when reacting with Lewis bases, resulting in boron adducts.

Uses

• Because of its exothermic interaction with water, borane was used as a solid fuel in rocket propulsion before the invention of technology.

Anomalous properties of boron

The members of the Boron family, found in group 13 in the periodic table, show a range of chemical and physical properties. Their electronic configuration is as follows: ns²np¹. This family includes:

• Boron(B)
•  Aluminium(AI)
•  Gallium(Ga)
• Indium(In)
• Thallium(TI)
• Nihonium(Nh)

While the physical and chemical properties of boron family members follow a common trend, properties of the element boron differ. This is because of the boron’s smaller size and lack of the d orbital. As a result of these differences properties of Boron are classified as anomalous properties of Boron.

Why does boron show its anomalous behaviour?

Boron is found to have properties that are in contrast to the other elements of the boron family due to its smaller size and lack of d-electrons. These are referred to as boron’s abnormal properties. Some of these strange characteristics are described below:-

Anomalous Behaviour of Boron

• The boron family compounds, other than boron itself  form tetrahedral [M(OH)₄]^– and octahedral [M(H₂O)₆ ]³⁺ in an aqueous medium
• Due to the lack of d orbitals, boron has a maximum covalence of 4
• Boron is neither a metal nor a non metal. It is a metalloid, whereas the others are post-transition metals
• The hydroxides and oxides formed from the boron element are acidic, whereas the hydroxides and oxides of the other elements in the family are amphoteric

Trends Shown by Members of Boron Family

• Tri-chlorides, bromides, and iodides are formed when members of the boron family react with halogens. These halides are hydrolyzed in water and are covalent in character
• In an aqueous medium, compounds of these elements such as tetrahedral [M(OH)₄]^– and octahedral [M(H₂O)₆ ]³⁺ (where M designates a member of the boron family) occur
• These trihalides are powerful Lewis acids due to their electron deficiency
• As we progress from boron to thallium, the metallic character becomes more prominent
• Because of differences in atomic size, the electronegativity of the elements drops down the group from B to Al, then increases significantly

Boron is an important element in the periodic table. It forms compounds such as Borax, Boric Acid, and Diborane. Unlike other members of the 13th group, Boron shows anomalous behaviour.