Hydrides Ionic hydrides Covalent Hydrides

HYDRIDES
	Binary compounds of hydrogen are known as hydrides.
	TYPES OF HYDRIDES
	There are six types of hydrides.
	Ionic hydrides Covalent Hydrides Polymeric Hydrides Metallic Hydrides Border line Hydrides Complex Hydrides
	IONIC HYDRIDES
	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-
	GENERAL FORMULA
	For the hydrides of group I-A
	MH
	Where M represents Li, Na, K, Rb, Cs and Fs
	EXAMPLES
	LiH, NaH, KH, RbH, etc. For the hydrides of group II-A
	MH2
	Where M represents Ca, Sr and Ba
	EXAMPLES
	CaH2, SrH2 , BaH2
	METHODS OF PREPARATION
	Ionic hydrides can be prepared directly on passing hydrogen gas over hot alkali metals or alkaline earth metals.
	GENERAL EXPRESSION OF PREPARATION
	For the hydrides of group I-A 2M + H2è 2MH
	For the hydrides of group II-A M + H2 è MH2
	EXAMPLES
	For the hydrides of group I-A
	2Li +H2 è 2LiH 2K + H2 è 2KH 2Rb + H2 è 2RbH 2Na + H2 è 2NaH
	For the hydrides of group II-A
	Ca + H2 è CaH2 Sr + H2 è SrH2 Ba + H2 è BaH2
	PHYSICAL PROPERTIES OF IONIC HYDRIDES
	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.
	USES OF IONIC HYDRIDES
	To produce hydrogen gas. Reducing agent in metallurgical process. Dehydrating agent for organic solvents.
	CHEMICAL PROPERTIES OF IONIC HYDRIDES
	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
	With HCl: For I-A NaH + HCl è NaCl + H2 LiH + HCl è LiCl +H2 KH + HCl è KCl + H2 For II-A CaH2 + 2HCl è CaCl2 + 2H2 BaH2 + 2HCl è BaCl2 + 2H2 SrH2 + 2HCl è SrCl2 + 2H2
	With Ethyl Alcohol:
	C2H5OH + NaH è C2H5ONa + H2 2C2H5OH + CaH2 è (C2H5O)2Ca + 2H2
	COVALENT HYDRIDES
	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
	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.