Hydrides
Chapter Name : Hydrogen |
Sub Topic Code : 102_11_09_05_02 |
Topic Name : Hydrides |
|
Sub Topic Name : Covalent Or Molecular Hydride |
|
Introduction
Hydrogen form molecular compounds with p-block elements (B, C, N, O, F;
Si, P, S, Cl; Ga, Ge, As, Sb, Br; In, Sn, Sb, Te, I; Tl, Pb, At). Common
examples of such hydrides are CH3, NH3, H2O,
HF etc.
Pre-Requisites:
Covalent
hydride, van der Waals’ forces of attraction
Activity:
Electrolysis of
solution of saline hydride in molten alkali halide produces H2 at
anode. Saline hydrides react explosively with water.
NaH(s) + H2O(aq)
? NaOH(aq) + H2(g)
The fire so
produced cannot be extinguished by CO2 as it gets reduced by
the hot metal hydride. Only sand is useful, as it is a solid.
Real Life Question:
Why hydrides are called covalent hydrides?
Key Words / FlashCards
| Key Words | Definitions (pref. in our own words) |
|---|---|
| Covalent hydride | Covalent hydrides are primarily compounds of hydrogen and nonmetals, in which the bonds are evidently electron pairs shared by atoms of comparable electronegativities. |
| van der Waals’ forces of attraction | Van der Waals forces include attractions and repulsions between atoms, molecules, and surfaces, as well as other intermolecular forces. They differ from covalent and ionic bonding in that they are caused by correlations in the fluctuating polarizations of nearby particles. |
Learning aids / Gadgets
| Gadgets | How it can be used |
|---|---|
| Water, drain clog removal (containing sodium hydroxide) + aluminium foil | When water is added to a drain clog removal liquid in the presence of aluminium ( using aluminium foil) , hydrogen gas is liberated. This is an exothermic reaction. |
Real life uses :
Hydrides that are soluble in common solvents are
widely used in organic synthesis. Particularly common are sodium
borohydride (NaBH4) and lithium aluminium hydride and
hindered reagents
Places to visit :
Chemistry
lab
Practical examples around us
| Examples | Explainations |
|---|---|
| Hydrogen as a fuel | Hydrogen is commonly used in the petroleum and chemical industries and is also widely used for many physics and engineering applications such as welding or as a coolant. |
What you learn in Theory:
•
Covalent
hydrides usually consist of discrete covalent molecules which are held together
by weak van der Waals’ forces of attraction and hence are called covalent or
molecular hydrides.
•
Depending
upon the number of electrons and bonds present in their Lewis structures :
1.
Electron
deficient hydrides (group 13)
2.
Electron exact hydrides (group 14)
Electron
rich hydrides (group 15, 16, 17)
What you learn in Practice:
Covalent hydrides are usually volatile compounds having low melting and
boiling points and also do not conduct electricity.