Hydrogen is the first element in the periodic table because it has atomic number one, which means that it has only one proton in its atom and thus only one electron in its outermost shell. The placement of elements in the periodic table is based on their electronic configuration.
Position of Hydrogen in Periodic Table
|Oxidation States||1, -1|
|Atomic Radius||78 pm|
|Boiling Point||-252.87° C|
|At Room Temperature||Colorless & Odorless Diatomic Gas|
What is the Position of Hydrogen in the Modern Periodic Table?
Hydrogen is an element that possesses unique properties. It has one electron in its valence shell similar to alkali metals and resembles them in several properties. Therefore, it should be placed in group 1 along with the alkali metals.
On the other hand, like halogens of group 17, only one electron needs to attain the stable noble gas configuration. Hence, it also resembles halogens and can be grouped with them in group 17. Thus, the position of hydrogen is debatable.
Differences with Metals
Hydrogen is a non-metal element. In its outer shell, it has only one electron and cannot lose this electron easily for gaining the electropositivity. However, alkali metals can easily lose electrons to gain electropositivity. At room temperature hydrogen is gas but alkali metals are solids. The hydrogen ion is much smaller than the ions of alkali metals. Hydrogen has an ionization potential that is more than the 300 Kcal per mole. However, the maximum ionization potential for the alkali metals is only 147 Kcal per mole.
Similarities of Hydrogen to Metals
If hydrogen gains one electron then its valance shell is completed. There are seven electrons in the valance shells of halogens and by gaining one electron they can gain the configuration of the noble gas. The electronegative nature of halogens and hydrogen is the same. Both halogens and hydrogen form the diatomic molecules.
Difference with Halogens
There is only one electron in the outer shell of hydrogen while halogens have seven electrons in their valance shells. The size of the hydrogen ion is much small than the size of the halogen ions. The reason is that hydrogen possesses only one proton and electron so the pull of the nucleus is much less. The hydrogen ion is unstable in the water while the ions of halogens are stable.
NCERT MCQ Questions for Class 11 Chemistry with Answers
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