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The lightest element, hydrogen, has the most straightforward electronic configuration, 1s1, consisting of a proton and a single electron. Ordinary elemental hydrogen exists as a diatomic molecule, called dihydrogen. Binary compounds formed by various elements with hydrogen are called hydrides. They are formed when hydrogen combines with other element coordinates except for noble gases to undergo different reactions.
Occurrence of Dihydrogen
In the Universe, Dihydrogen is an element present in larger quantities. Approximately 70% of the total mass in the atmosphere. It is also defined as the main element of the solar atmosphere.
Planets like Jupiter and Saturn mainly consist of Hydrogen gas. However, if we speak about the earth’s atmosphere, it is present in lesser quantities for approximately 0.15% of the total mass because of its lightweight.
Considering the total combination of the earth’s crust and the ocean, it comprises 15.4% of the total mass.
The presence of dihydrogen leaving water is present in animal and plant tissues. Not only this, but it is also present in proteins, carbohydrates, and other compounds.
The Reaction of Hydrogen with Chlorine
Dihydrogen acts as a reducing agent to reduce chlorine into chloride (Cl– ) ion and, in turn, gets oxidised to H+ ion. Hence, it forms hydrogen chloride in which H and Cl share an electron pair, leading to a covalent molecule.
H2 + Cl2 → 2HCl
The Reaction of Hydrogen with Sodium
Sodium reduces dihydrogen and becomes NaH. This reaction involves the transfer of an electron from Na to H, resulting in an ionic compound, Na+ H–.
H2 + 2Na → 2NaH
The Reaction of Hydrogen with Copper
Dihydrogen reacts with copper(II) oxide and reduces it to copper in a zero oxidation state. Dihydrogen oxidises to H2O at the same time, which is a covalent molecule.
CuO(s) + H2(g) → Cu(s) + H2O(l)
Hydrides
Hydrides are formed by negatively charged particles, electrons, of a hydrogen atom when they react with other elements to create a binary compound. Except for the noble gases, different periodic parts react with Hydrogen gas to form various hydrides. In hydrides, hydrogen generally exists in an oxidation number of -1. Electronegativity of an element, which is the ability of an atom to attract electrons towards itself and hence the type of bond formed, determines the kind of hydride it would form with hydrogen.
Different Categories Of Hydrides
Taking into consideration the formation of different elements with chemical bonds. Hydrides are divided into three categories which are:
- Ionic Hydrides or Saline or Salt like hydrides.
- Covalent or molecular Hydrides
- Metallic or Interstitial Hydrides.
Ionic Hydrides or Saline or Salt like Hydrides:
Ionic hydrides are also known as Saline Hydrides or pseudohalides. Compounds of Hydrogen with strongly electropositive metals, i.e., alkali and alkaline earth metals and some highly positive members of lanthanide series, except for Be and Mg, are called Ionic hydrides.
Some of the examples of Ionic Hydrides are Sodium hydride (NaH), Lithium Hydride (LiH), and Potassium Hydride(KH).
These hydrides also act as a reducing agent. Ionic hydrides are converted into hydrogen to produce quality fuel material during the heating process.
Covalent or Molecular Hydrides:
When elements are covalently bonded with hydrogen, they form covalent hydrides. Covalent hydrides are formed by all the true nonmetals (except zero group elements), and the elements like Al, Ga, Sn, Pb, Sb, Bi, Po, etc., are usually metallic. This type of hydride could be volatile or non-volatile.
Non-metallic hydrides end up with more electronegativity on a periodic table as it crosses from group 13 to 17. Hence, they become less capable of donating an electron.
Some of the examples of Covalent Hydrides are Boron Hydride and Nitrogen Hydride. Due to solubility in common solvents, they are used in organic synthesis—for example, sodium borohydride.
Metallic or Interstitial Hydrides
Metal Hydrides are commonly defined as binary compounds of hydrogen and metal. They are also known as blended metallic hydrides.
Since the hydrogen atom is smaller, it occupies more space in the metallic lattice, thus producing distortion. Hence, they are also called Interstitial hydrides. They tend to absorb a large amount of hydrogen on the surface.
The hydrides of N, O, and F have lower boiling points than the hydrides of their subsequent group members.
The molecular masses of NH3, H2O, and HF require that their boiling points be lesser than those of the subsequent group member hydrides. However, the electronegativity of N, O, and F is higher, so the magnitude of hydrogen bonding in their hydrides will be more. Hence, the boiling points of NH3, H2O, and HF are higher than the hydrides of their subsequent group members.
Phosphorus with outer electronic configuration 3s2 3p3 cannot form PH5?
Although phosphorus exhibits +3 and +5 oxidation states, it cannot form PH5. Besides some other considerations, the high ΔaH value of dihydrogen and ΔegH value of hydrogen do not favour exhibiting the highest oxidation state of P and, consequently, the formation of PH5.
Conclusion
The binary compounds of hydrogen with metals are known as hydrides. The hydrides are of three types, ionic, metallic and covalent compounds.
Hydrides are used as drying agents in the textile industry and mainly as reducing agents. It can be formed by dissolving hydrogen in water. These are compounds that comprise an element connected to a hydrogen element.
