Types of Hydrogen (Isotopes of hydrogen)

 

Hydrogen

Electronic Structure of Hydrogen

Hydrogen has the simplest atomic structure of all the elements, and consists of a nucleus containing one proton with a charge +1 and one orbital electron. The electronic structure may be written as 1s¹.

Atoms of hydrogen may attain stability in there different ways:

By forming an electron pair (covalent ) bond with another atom. Non-metals typically form this type of bond with hydrogen, for example H₂, H₂O, HCl or CH₄.

By losing an electron to form H⁺ . A proton is extremely small, so it has a very high polarizing power, and therefore distorts the electron cloud on other atoms. Thus protons are always associated with other atoms or molecules. For example, in water or aqueous solutions protons exist as H₃O⁺ ions. Free protons do not exist under normal conditions.

By gaining an electron to form H^- . Crystalline solids such as LiH contain the H^- ion and are formed by highly electropositive metals (all of Group I, and some of Group II).

Since hydrogen has an electronegativity of 2.1 , it may use any of the three methods, but the most common way is forming covalent bonds.

Position of Hydrogen In Periodic Table

Hydrogen is the first element in the periodic table, and is unique. There are only two elements in the first period, hydrogen and helium. Hydrogen is quite reactive, but helium is inert.

The properties of hydrogen cannot be correlated with any of the main groups in the periodic table, and hydrogen is considered on its own.

The structure of hydrogen atoms is in some ways like that of the alkali metals. The alkali metals (Group l) also have just one electron in their outer shell, but tend to lose this electron in reactions and form positive ions M⁺.  Hydrogen has much greater tendency to pair the electron and form covalent bond.

The structure of hydrogen atoms is in some ways like that of the halogens (Group Vll), since both are one electron short of a noble gas structure.

In some ways the structure of hydrogen resembles that of the Group lV elements, since both have a half filled shell of electrons.

Abundance of Hydrogen

Hydrogen is the most abundant element in the universe. Some estimates are that 92% of the universe is made up of hydrogen, and 7% “helium, leaving only 1% for all of the other elements.

However, the abundance of H₂ in the earth’s atmosphere is very small. This is because the earth’s gravitational field is too small to hold so light an element, though some H₂ is found in volcano gases.

In contrast, hydrogen is the tenth most abundant element in the earth’s crust. It also occurs in vast quantities as water in the oceans.

 Isotopes of Hydrogen (How many isotopes of hydrogen):

 Isotopes: are atoms of the same element but have different mass numbers.

Naturally occurring hydrogen contains : protium  ₁¹H or H, deuterium ₁²H or D, and tritium ₁³H or T. Protium is the most abundant.

 These isotopes have the same electronic configuration and have essentially the same chemical properties. The only differences in chemical properties are the rates of reactions for example:

• H₂ is more rapidly adsorbed on to surfaces than D₂.
• H₂ reacts with Cl₂ over 13 times faster than D₂ , because H₂ has a lower energy of activation.

Isotope effects: differences in properties which arise from differences in mass.

Deutrium can be separated by electrolysis of water where H₂ is liberated much faster than D_2.

Protium bonds are broken more readily than deuterium bonds.

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 A. Deutrium Compounds:

Deuterium compounds are prepared from D₂ or D₂O

                            (i)            Deuterium compounds are prepared from D₂ by “exchange reactions" where deuterium is exchanged for hydrogen in compounds.  For example, D₂ reacts with H₂ at high temperatures, forming HD and it also exchanges with NH₃ and CH₄ to give NH₂D, NHD₂, ND₃; and CH₃D-CD₄.

                         (ii)            Deuterium compounds are prepared from D₂O by direct reactions, or by exchange reactions.

 Exchange reactions

Direct reactions

 

           

 B.  Tritiated compounds:

 Tritiated compounds can be made from T₂ gas  for example T₂O gas

 Uses of Tritium:

     1)    used in thermonuclear devices.

2)    used for research into fusion reactions.

3)    used as a radioactive tracer, since it is relatively cheap.

Types of Hydrogen (Ortho and Para Hydrogen):

 

§  In hydrogen molecule H₂, the direction of spin of hydrogen nucleus gives spin isomerism. Therefore, H₂ exists in two different forms known as ortho and para hydrogen.

 

§  Ortho Hydrogen: The two nuclei spin in the same direction

§   Para Hydrogen The two nuclei spin in the opposite direction.

 

§  The para form has the lower energy, and the more stable form of hydrogen. 

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