Group Iii-a and Grpup Iv-a Elements

Q.1      why Boron is non metal ?

Ans :    The smaller atomic size and high nuclear charge boron is non – metal. Moreover

, boron has high I.E and high E.N make it poor conductor. Due to all these conditions boron is non – metal

Q.2      B3+ ion does not exist but Al3+ ion does why?

Ans :    The size of boron ion is very small. Due to greater polarizibility is forms covalent compounds .While aluminum forms ionic compound in water it give Al3+ ions.

How the solubility of Borax change with the change in temperature?

Ans.     Borax is spariringly soluble in cold water 3 g is dissolved in l00grams of water at 100C. At 1000C, 99. 3g of H3 BO3 become soluble in 100g of water.

Q.6      How the temperature influences the water of crystallization of Borax?

Ans :    Below 62oC decelerated crystals are formed. Above 600C octahedral crystals of pentahydrated borax are obtained.

Q.17    What is the utility of this reaction when Al reacts with O2?

Ans:     Al reacts with O2 and this reaction is highly exothermic. This heat can be used for melting of those metals whose oxides are reduced by Al powder.

Q 18    Why CO2 is gas and SiO2 is solid at room temperature?

Ans:     CO2 has independent existence and it has weak intermolecular forces due to linear structure. In CO2 double bonds are present between carbon and oxygen which make it more stable.

In case of SiO2 size of Si atom is much larger than carbon atom. Greater no. of oxygen atoms can surround Si atom. SiO2 has network covalent structure. Each silicon is attached with four oxygen atoms and each oxygen is attached with two Si atom.

Q. 19   Why CO is polar while CO2 is non polar?

Ans:     CO is diatomic molecule . It has triple bonds between C and O. Two bonds are covalent bonds while one bond is co-ordinate covalent bond. The electron pair is donated by oxygen to carbon atom. Oxygen gets partial positive charge while carbon gets partial negative charge.