Isotopes of Hydrogen - Practice Questions & MCQ

About Hydrogen :

• Hydrogen is the first element in the periodic table. However, its placement in the periodic table has been a subject of discussion in the past.
• Hydrogen is the lightest atom with only one electron.
• Hydrogen has the simplest atomic structure among all the elements around us in Nature.
• In atomic form it consists of only one proton and one electron. However, in elemental form it exists as a diatomic (H2) molecule and is called dihydrogen.
• It forms more compounds than any other element.

Isotopes of Hydrogen : Hydrogen has 3 isotopes. And these isotopes differ from each other because of presence of different number of neutrons.

1. Protium, 
2. Deuterium,  or D
3. Tritium,  or T

Since the isotopes have the same electronic configuration, they have almost the same chemical properties. The only difference is in their rates of reactions, mainly due to their different enthalpy of bond dissociation However, in physical properties these isotopes differ considerably due to their large mass differences.

Debatable position of Hydrogen in periodic table:

Hydrogen has electronic configuration 1s¹ . On one hand, its electronic configuration is similar to the outer electronic configuration (ns¹ ) of alkali metals , which belong to the first group of the periodic table. On the other hand, like halogens (with ns 2np⁵ configuration belonging to the seventeenth group of the periodic table), it is short by one electron to the corresponding noble gas configuration, helium (1s² ). Hydrogen, therefore, has resemblance to alkali metals, which lose one electron to form unipositive ions, as well as with halogens, which gain one electron to form uni negative ion. Like alkali metals, hydrogen forms oxides, halides and sulphides. However, unlike alkali metals, it has a very high ionization enthalpy and does not possess metallic characteristics under normal conditions. In fact, in terms of ionization enthalpy, hydrogen resembles more with halogens, ∆i H of Li is 520 kJ mol–1, F is 1680 kJ mol–1 and that of H is 1312 kJ mol–1. Like halogens, it forms a diatomic molecule, combines with elements to form hydrides and a large number of covalent compounds. However, in terms of reactivity, it is very low as compared to halogens. Hence due to it's unique behaviour, it is placed separately in the periodic table.