Question

Boron has an extremely high melting point because of:
a.) The strong van der waals forces between its atoms
b.) The strong binding forces in a covalent polymer
c.) Its ionic crystal structure
d.) Allotropy

Answer 1

Hint: Electronic configuration of Boron atom makes it a unique element, as it has only 3 electrons in its valence shell so it is trivalent; also it is the element of second period and exists on the little right side in periodic table that gives it a small size. Now small size and trivalency, allows it to make covalent bonds with neighboring atoms in its pure form.

Complete Solution :
Boron:
Atomic number: 5
- Physical properties: Pure boron is a black, lustrous, metalloid that conducts electricity at high temperatures and behaves like an insulator at low temperatures that makes it a semiconductor.
 - Its melting point is 2352 K and boiling point is 2823 K.
- Boron occurs as an orthoboric acid in some volcanic spring waters, and as borates in the minerals borax and colemanite. However, by far the most important source of boron is rasorite.
- Boron has a high melting point of 2352 K because of its small atomic size, it forms strong covalent bonds with the adjacent atoms. Thus boron atoms have a close packed structure in its solid state therefore a large amount of heat is required to break the bonds between Boron atoms. That is why boron has an extremely high melting point.
 - As boron is trivalent therefore in its compounds boron atoms only has 6 electrons and an empty orbital. This empty orbital makes its compound behave like a lewis acid.
So, the correct answer is “Option B”.

Note: Boron has been an ignition source in some rockets. Boron is also used to make glass, ceramics, and enamels etc. Its compounds are used for water softeners, soaps, detergents, agricultural chemicals, pest controls, fire retardants, fireworks, and medicines, which are commercial uses.