Question

Grade 11 chemistry write the types of hydrides

Answer 1

✔️Anion of hydrogen is called hydride.


✔️ Compound in which one or more hydrogen centres have nucleophilic, reducing, or basic properties are also called hydrides.
Types of Hydrides

⏹Ionic hydrides :-

➖They have significant ionic bonding character.

➖ Ionic or saline hydride, is a hydrogen atom bound to an extremely electropositive metal.

example:-

C6H5C(O)CH3 + KH → C6H5C(O)CH2K + H2





⏹Covalent hydrides:-

➖They include the hydrocarbons and many other compounds which covalently bond to hydrogen atoms.

➖This includes hydrides that exist as discrete molecules, polymers or oligomers, and hydrogen that has been chem-adsorbed to a surface


⏹Interstitial hydrides:-

➖ which may be described as having metallic bonding (exist within metals or alloys).

➖These systems are usually non-stoichiometric.

Answer 2

¤ Dihydrogen combines with almost all the elements, except noble gases under suitable conditions to form binary compounds called hydrides.

=>These can be represented as EHx (or) EmHn, where E is the symbol for an element.

EHx → MgH2
Where x = number of hydrogen atoms

EmHn → B2H6
Where m = number of atoms of elements E and n = number of hydrogen atoms

There are three types of hydrides depending on the behaviour and the nature of the bond formed between the hydrogen atom and the element.

=>The types of hydrides are:
1. ionic or saline or salt-like hydrides
2.covalent (or) molecular hydrides
3. metallic (or) non-stoichiometric hydrides

A] Ionic (or) salt-like hydrides.

=>These are stoichiometric compounds of dihydrogen formed with most of the s-block elements which are highly electropositive in character.

=>The ionic hydrides are crystalline, non-volatile and nonconducting in solid state. 

=>However, their melts conduct electricity and on electrolysis liberate dihydrogen gas at anode, which confirms the existence of H– ion.

***=>Saline hydrides react violently with water producing dihydrogen gas.

NaH(s) + H2O(aq) → NaOH(aq) + H2(g)

***=>Lithium hydride is rather unreactive at moderate temperatures with O2or Cl2. It is, therefore, used in the synthesis of other useful hydrides,
e.g:

8LiH + Al2Cl6 → 2LiAlH4 + 6LiCl
2LiH + B2H6 → 2LiBH4

B] Covalent or Molecular Hydride

=>Dihydrogen forms molecular compounds with most of the p-block elements.
Examples are CH4, NH3, H2O and HF.
=> Being covalent, they are volatile compounds.

=>Molecular hydrides are further classified according to the relative numbers of electrons and bonds in their Lewis structure into :
(i) electron-deficient,
(ii) electron-precise, and
(iii) electron-rich hydrides.

C] Metallic or Non-stoichiometric (or Interstitial ) Hydrides

=>These are formed by many d-block and f-block elements. However, the metals of group 7, 8 and 9 do not form hydride.

=>Even from group 6, only chromium forms CrH.

=> These hydrides conduct heat and electricity though not as efficiently as their parent metals do.

For example, LaH2.87, YbH2.55, TiH1.5-1.8, ZrH1.3-1.75, VH0.56, NiH0.6-0.7, PdH0.6-0.8etc.