Boron and Silicon

Notes

Introduction to Boron, Silicon and periodic Position

Boron forms a number of hydrides (such as BH3, B2H6, B4H10, B5H9 etc). These are called boranes. BH3 is unstable, B2H6 has a stable bridged structure which is known as diborane. Boranes possessing the general formula BnHn+4 and BnHn+6 are well known. Among these the most important borane is diborane. Boranes are volatile and covalent in nature. The two boron atoms and four hydrogen atoms lie in the same plane, the two bridging hydrogen atoms lie symmetrically one above and the other below in a plane perpendicular to this plane. B2H6 has a three center-electron pair bond. Borax glass is the anhydrous form of borax and is obtained by heating the borax above its melting point until all the molecules of water of crystallization are removed. Silicon is the element which is next to oxygen in abundance in the earth's crust. It's an important constituent of igneous rocks which consist of silicates of magnesium, aluminium, potassium or iron. Silicon is widely present as silica (SiO2) in the form of sand, quartz, and flint. Amorphous silicon can be extracted when well-powdered quartz is mixed with magnesium powder and heated in a fire clay crucible along with the certain quantity of calcined magnesia (MgO).

Boron and Silicon

Boron is extracted from borax. On heating boric acid, boric acid dehydrates and finally gives boric anhydride. Crystalline boron is inert chemically. Boron is better to term it as semiconductor than a conductor. Borax is used as antiseptic. Boric acid is also known as orthoboric acid due to electron deficient nature of boron. Diborane is found in dimer form.