Binary Compounds of Hydrogen , Hydride and the Classification of Hydrides:-

Definition Of Hydrides

  Hydrogen combines with other elements and forms binary compounds which are called Hydrides. Hydrogen forms binary compounds with all types of elements metals and non-metals excluding noble gases. Hydrides are classified into six major groups on the bases of nature of chemical bonding i.e (a) ionic hydrides (b) covalent hydrides (c) complex hydrides (d) Matallic hydrides (e) polymeric hydrides (f) Border line hydrides.

A) Ionic Hydrides:

       These types of hydrides are formed by the metals of IA group (alkali metals) and IIA group (alkaline earth metals) except Beryllium and Magnesium. In these hydrides, metal atoms acquire positive iob by losing valence electrons and hydrogen acquire negative ion by gaining the electron in the order to complete their shells, therefore these hydrides are known as "Ionic Hydrides". Also they possess salt like character, therefore they are called salt like or saline hydrides . They are strong reducing agent.

Preparation Of Ionic Hydrides:-
They are stable toward heat but their stability decreases in grouo from top to bottom. They are colourless, non-volatile and solublr in water but insoluble in organic solvents. They produce hydrogen gas when react with water, acids and alcohols, generally CaH2 is used to prepare hydrogen gas. Reaction with acids, water and alcohol are vigorous with hydrides of alkali-metals than alkaline earth metals.

B) Covalent Hydrides:

P-block elements, excluding noble gases, form covalent hydrides with hydrogen. The nature of chemical bond is covalent therefore they are known as covalent hydrides. They can be prepared by various methods e.g hydrogen when ignited with oxygen formed water and H2S gas is formed when sulphur is heated at 450 celsous and HCL is formed in sunlight as given under:

Preparation 
1) H2 + Cl2 ----> 2HCL
2) ‎H2 + S ----> H2S
3) ‎CaC2 + 2H2O ----> Ca(OH)2

Properties
i) They are colourless gases or volatile liquids with low boiling points except water which has higher boiling point i.e 100 celsius due to polarity.
ii) Hydrides of IIIA $ IVA group members are neutral e.g CH4 and BH3 etc
iii) Hydrides of VA group member are basic in nature e.g NH3 , PH3 etc while hydrides of VIA $ VIIA group members are acidic in nature and their acidity increases from left to right top to bottom e.g Acidic strenght in ascending order is H2O < H2S < SeH2.

C) Complex Hydrides:

Hydrides of IIIA grouo members are unstable except BH2. When hydrides of IA and IIIA elements combine each other complex hydrides are formed, as they possessing all three types of chemical bonds therefore they are complex. Their general formula is ABH4 where 'A' represents univalent alkali metals while 'B' indicates trivalent IIIA elements.

Properties:
These compounds are salt like while solids, stable up to 300 celsius They are soluble in water in which they ionize ti give Li and AlH4 ions AlH4 ions immediately reacts with water to produced hydrogen as
NaAlH4 + H2O ----> Al(OH)3 + NaOH + H2

Metalic Hydrides:

 They are also known as 'interstitial hydrides' or 'Non-stoichiometric' or Non-chemical hydrides b/c hydrogen forms hydrides of intermediate composition with transition metals by penetrating the crystal lattice structure of these metals without any chemical composition. Interstitial means empty space. Atomic hydrogen is obtained on heating such hydrides due to this characteristic they are used as 'Reducing Catalyst' or hydrogenation catalyst e.g platinum, Palladium and Nickel.
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E) Polymeric Hydrides:

Hydrides of (BeH2) and  (MgH2) of IIA group elements are polymerized with each other therefore they are known as polymeric hydrides. Their properties are intermediate b/w ionic hydrides and covalent hydrides.

F) Border Line Hydrides:-

These hydrides are formed by metals of IB, IIB and with the few members of IIIA such as Indium and thallium. Their properties are the intermediate between the metallic and covalent hydrides.

Isotopes:-

The existance of isotopes of elements was first discover by the J.J Thomson in (1912-1913). Isotopes are defined as
(i) Atoms of the same elements having same atomic structure but different atomic mass.
(ii) Atoms that have the same number of protons but different number of neutrons in their respective nuclei.

Isotopes Of Hydrogen:-

Protium or Ordinary Hydrogen:
It is an ordinary form of hydrogen. It is represented by H or P. It contains one proton in the nucleus and one electron in Is orbital. Its atomic number is one and mass number is also one. It is naturally free occuring hydrogen in the form of compounds with other element contain about 99.98% protium. Electronic structure of protium is:
1 = electron
1 = proton
0 = neutron.
Deutrium:-
It is the heavy hydrogen. It is represented by the H2 Or D2. It contain one proton and one neutron. Its atomic number is one and mass number is two. It is present in naturally occuring hydrogen about 0.0156% i.e in ratio is 1:15000. The existance of heavy hydrogen by Birge and Menzel in 1931. Electronic structure of Deutrium is:
1 = Electron
1= Proton
1= Neutron.

Tritium:-
It is the heaviest form of hydrogen and rarely occure in nature. It has one atomic number and three atomic mass. Electronic structure of Tritium is:
1= Electron
1= Proton
2= Neutron.