Why boron is a non metal

Many of the anomalous properties of the group 13 elements can be explained by the increase in Z eff moving down the group. Isolation of the group 13 elements requires a large amount of energy because compounds of the group 13 elements with oxygen are thermodynamically stable. Boron behaves chemically like a nonmetal, whereas its heavier congeners exhibit metallic behavior. Instead of forming a metallic lattice with delocalized valence electrons, boron forms unique aggregates that contain multicenter bonds, including metal borides, in which boron is bonded to other boron atoms to form three-dimensional networks or clusters with regular geometric structures.

All neutral compounds of the group 13 elements are electron deficient and behave like Lewis acids. The trivalent halides of the heavier elements form halogen-bridged dimers that contain electron-pair bonds, rather than the delocalized electron-deficient bonds characteristic of diborane.

Their oxides dissolve in dilute acid, although the oxides of aluminum and gallium are amphoteric. None of the group 13 elements reacts directly with hydrogen, and the stability of the hydrides prepared by other routes decreases as we go down the group.

Learning Objectives To understand the trends in properties and the reactivity of the group 13 elements. Preparation and General Properties of the Group 13 Elements As reductants, the group 13 elements are less powerful than the alkali metals and alkaline earth metals.

Reaction with F 2 gives the trifluorides MF 3 for all group 13 elements. Reactions and Compounds of Boron Elemental boron is a semimetal that is remarkably unreactive; in contrast, the other group 13 elements all exhibit metallic properties and reactivity. Unlike metallic solids, elemental boron consists of a regular array of B 12 icosahedra rather than individual boron atoms.

Note that each boron atom in the B 12 icosahedron is connected to five other boron atoms within the B 12 unit. Solution: Molecular oxygen is an oxidant. If the other reactant is a potential reductant, we expect that a redox reaction will occur.

Because hydride is a strong reductant, a redox reaction will probably occur. A reasonable guess is B 2 O 3 and H 2 O, both stable compounds. Neither BCl 3 nor water is a powerful oxidant or reductant, so a redox reaction is unlikely; a hydrolysis reaction is more probable.

Nonmetal halides are acidic and react with water to form a solution of the hydrohalic acid and a nonmetal oxide or hydroxide. In this case, the most probable boron-containing product is boric acid [B OH 3 ]. We normally expect a boron trihalide to behave like a Lewis acid.

In this case, however, the other reactant is elemental hydrogen, which usually acts as a reductant. Consequently, we can write a redox reaction in which hydrogen is oxidized and boron is reduced. Because compounds of boron in lower oxidation states are rare, we expect that boron will be reduced to elemental boron. The other product of the reaction must therefore be HI. Of the group 13 halides, only the fluorides behave as typical ionic compounds. Complexes of Group 13 Elements Boron has a relatively limited tendency to form complexes, but aluminum, gallium, indium, and, to some extent, thallium form many complexes.

Silicon compounds of the general formula SiX 4 , where X is a highly electronegative group, can act as Lewis acids to form six-coordinate silicon.

Antimony reacts readily with stoichiometric amounts of fluorine, chlorine, bromine, or iodine, yielding trihalides or, with excess fluorine or chlorine, forming the pentahalides SbF 5 and SbCl 5. Depending on the stoichiometry, it forms antimony III sulfide, Sb 2 S 3 , or antimony V sulfide when heated with sulfur. As expected, the metallic nature of the element is greater than that of arsenic, which lies immediately above it in group These nonpolar molecules contain boron with sp 2 hybridization and a trigonal planar molecular geometry.

The fluoride and chloride compounds are colorless gasses, the bromide is a liquid, and the iodide is a white crystalline solid. Except for boron trifluoride, the boron trihalides readily hydrolyze in water to form boric acid and the corresponding hydrohalic acid. Boron trichloride reacts according to the equation:. Boron trifluoride reacts with hydrofluoric acid, to yield a solution of fluoroboric acid, HBF 4 :.

In this reaction, the BF 3 molecule acts as the Lewis acid electron pair acceptor and accepts a pair of electrons from a fluoride ion:. All the tetrahalides of silicon, SiX 4 , have been prepared. Silicon tetrachloride can be prepared by direct chlorination at elevated temperatures or by heating silicon dioxide with chlorine and carbon:.

It is possible to prepare silicon tetrafluoride by the reaction of silicon dioxide with hydrofluoric acid:. Hydrofluoric acid is the only common acid that will react with silicon dioxide or silicates. This reaction occurs because the silicon-fluorine bond is the only bond that silicon forms that is stronger than the silicon-oxygen bond. For this reason, it is possible to store all common acids, other than hydrofluoric acid, in glass containers. Except for silicon tetrafluoride, silicon halides are extremely sensitive to water.

Upon exposure to water, SiCl 4 reacts rapidly with hydroxide groups, replacing all four chlorine atoms to produce unstable orthosilicic acid, Si OH 4 or H 4 SiO 4 , which slowly decomposes into SiO 2. Boric oxide dissolves in hot water to form boric acid, B OH 3 :. The boron atom in B OH 3 is sp 2 hybridized and is located at the center of an equilateral triangle with oxygen atoms at the corners.

In solid B OH 3 , hydrogen bonding holds these triangular units together. Complete water loss, at still higher temperatures, results in boric oxide. Borates are salts of the oxyacids of boron. Borates result from the reactions of a base with an oxyacid or from the fusion of boric acid or boric oxide with a metal oxide or hydroxide. Silicon dioxide, silica, occurs in both crystalline and amorphous forms.

The usual crystalline form of silicon dioxide is quartz, a hard, brittle, clear, colorless solid. It is useful in many ways—for architectural decorations, semiprecious jewels, and frequency control in radio transmitters. Silica takes many crystalline forms, or polymorphs , in nature.

The term quartz is also used for articles such as tubing and lenses that are manufactured from amorphous silica.

Opal is a naturally occurring form of amorphous silica. One solution to that problem, it has turned out, was to slim down to a single CAAC ligand — which Braunschweig has put to good use. Thanks to their partially filled d-orbitals, transition metals can give and take electrons, and thereby bind and activate a wide array of organic small molecules. FLPs offer one way to recapitulate this behaviour in low-cost, earth-abundant, non-toxic main group elements.

But borylenes, with their lone pair and unfilled p orbitals, can do it too, mimicking transition metal behaviour in a single boron atom centre.

In , Stephan and Bertrand showed a borylene could bind carbon monoxide. In , Braunschweig put this property to even more spectacular effect when he used it to activate dinitrogen, one of the most stable small molecules known. The process is essential for producing the fertiliser that keeps us all fed. Despite another 40 years of intense research, nitrogen fixation is one of those reactions we wish we could do a whole lot better than we can at the moment, he says.

Activating the triple bond in dinitrogen is just one of the powerful synthetic tricks boron compounds can perform. The dinitrogen study was preceded by computational screening, Braunschweig says.

You have to have a subtle balance between stability and reactivity. This complex could be further reduced to a nitrogen—nitrogen single bond. Nobody is predicting a boron-based replacement for the Haber—Bosch process, however. Braunschweig has that goal clearly in mind.

We see that this is a very interesting and worthwhile target to pursue. There are plenty more new compounds still to find, Stephan is sure. This time, the team coax dinitrogen gas to form a four-nitrogen chain between two borylene complexes, an unprecedented piece of nitrogen chemistry. A very common organic reaction under ordinary conditions has produced significant amounts of unexpected trans-products for the first time. Andy Extance discovers why the compound best known as a fertiliser is a surprising candidate to power enormous container ships.

The Royal Society of Chemistry aims to use Cop26 as a springboard to a more sustainable future. Rachel Brazil reports.

Already hailed as a miracle, the new vaccine technology could protect us from other diseases, Clare Sansom finds. Site powered by Webvision Cloud. Skip to main content Skip to navigation. Small-molecule boron chemistry has really come into vogue in the last 10 or 15 years But over the past decade, boron chemistry has been steadily subverted.

Related articles. When humans consume large amounts of boron-containing food, the boron concentrations in their bodies may rise to levels that can cause health problems. Boron can infect the stomach, liver, kidneys and brains and can eventually lead to death. When exposure to small amounts of boron takes place irritation of the nose, throat or eyes may occur. It takes 5 g of borc acid to make a person ill and 20 grams or more to put its life in danger.

Eating fish or meat will not increase the boron concentrations in our bodies, as boron does not accumulate within the tissues of animals. Boron is an element that occurs in the environment mainly through natural processes. Boron occurs naturally in the environment due to the release into air, soil and water through weathering. It may also occur in groundwater in very small amounts. Humans add boron by manufacturing glass, combusting coal, melting copper and through the addition of agricultural fertilizers.

The concentrations of boron that are added by humans are smaller that the naturally added concentrations through natural weathering. Boron exposure through air and drinking water is not very likely to occur, but the risk of exposure to borate dust in the workplace does exist.