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HYDRIDES
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| Binary compounds of hydrogen are known as hydrides. | ||||
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TYPES
OF HYDRIDES
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There are six types of hydrides. | |||
Ionic hydrides
Covalent Hydrides
Polymeric Hydrides
Metallic Hydrides
Border line Hydrides
Complex Hydrides |
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IONIC
HYDRIDES
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| Elements
of group I-A and II-A except Be and Mg form ionic hydrides. In these hydrides,
bond between metal atom and hydrogen atom is ionic. Ionic hydrides are also
known as Saline hydrides or Salt like hydrides because their properties
are identical to salts.
In ionic hydrides,hydrogen acts as H- |
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GENERAL
FORMULA
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| For the hydrides of group I-A | ||||
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MH
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Where
M represents Li, Na, K, Rb, Cs and Fs
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EXAMPLES
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| LiH,
NaH, KH, RbH, etc. For the hydrides of group II-A |
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| MH2 | ||||
| Where M represents Ca, Sr and Ba | ||||
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EXAMPLES
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| CaH2, SrH2 , BaH2 | ||||
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METHODS
OF PREPARATION
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| Ionic hydrides can be prepared directly on passing hydrogen gas over hot alkali metals or alkaline earth metals. | ||||
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GENERAL
EXPRESSION
OF PREPARATION |
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| For the hydrides of group I-A 2M + H2è 2MH | ||||
| For the hydrides of group II-A M + H2 è MH2 | ||||
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EXAMPLES
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| For the hydrides of group I-A | ||||
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2K + H2 è 2KH 2Rb + H2 è 2RbH 2Na + H2 è 2NaH |
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| For the hydrides of group II-A | ||||
| Ca
+ H2 è
CaH2 Sr + H2 è SrH2 Ba + H2 è BaH2 |
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PHYSICAL
PROPERTIES
OF IONIC HYDRIDES |
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Ionic hydrides are solids.
They are thermally very stable.
They have high melting and boiling point.
They are soluble in water.
They are insoluble in organic compounds.
They are conductors (electrolytes) of electricity. |
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USES
OF IONIC HYDRIDES
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To produce hydrogen gas.
Reducing agent in metallurgical process.
Dehydrating agent for organic solvents. |
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CHEMICAL
PROPERTIES
OF IONIC HYDRIDES |
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With Water For I-A NaH + H2O è NaOH + H2 LiH + H2O è LiOH + H2 KH + H2O è KOH + H2 For II-A CaH2 + 2H2O è Ca(OH)2 + 2H2 BaH2 + 2H2O è Ba(OH)2 + 2H2 SrH2 + 2H2O è Sr(OH)2 + 2H2 |
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With HCl: For I-A NaH + HCl è NaCl + H2 LiH + HCl è LiCl +H2 KH + HCl è KCl + H2
CaH2 + 2HCl è CaCl2 + 2H2 BaH2 + 2HCl è BaCl2 + 2H2 SrH2 + 2HCl è SrCl2 + 2H2 |
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| With Ethyl Alcohol: | ||||
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2C2H5OH + CaH2 è (C2H5O)2Ca + 2H2 |
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COVALENT HYDRIDES
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| Elements
of group III-A to VII-A form covalent hydrides. They
possess covalent bond in their structure. For
example: BH3, AlH3, CH4, NH3, H2S, HCl |
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| Method
of preparation Covalent hydrides can be prepared by two methods. Direct method N2 + 3H2 è 2NH3 H2 + S è H2S H2 + Cl2 è 2HCl Indirect method By the action of water on a suitable compound we can prepare different covalent hydrides. i) By Al4C3 Al4C3 + 6H2O è 2Al2O3 + 3CH4 ii) By Mg3N2 Mg3N2 + 6H2O è 3Mg(OH)2 + 2NH3 iii) By Ca3P2 Ca3P2 + 6H2O è 3Ca(OH)2 +2 PH3 (phosphene) iv) By PCl3 2PCl3 +6H2O è 2H3PO3 +6HCl Properties of covalent hydrides 1) Covalent hydrides are gases or liquids. e.g. Gases : CH4, NH3, H2S, Liquid : H2O, HCl 2) Liquids are volatile. 3) They have low melting and boiling points. 4) They are colorless compounds. Nature: 1) Hydrides of III-A and IV-A are neutral. 2) Hydrides of V-A are basic. 3) Hydrides of VI-A and VII-A are acidic. |
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us:
info@citycollegiate.com |
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