Describe The Position Of Hydrogen In Periodic Table?

 Position of an element in periodic table depends upon its electronic configuration and properties. Hydrogen resembles the elements of group I-A, IV-A and VII-A in some respects. Properties of hydrogen do not completely match any one of the above-mentioned groups. That is why position of hydrogen is still undecided.In the coming lines we will discuss why hydrogen can not be placed in a particular group in the periodic table.Resemblance Of Hydrogen With Alkali Metals(Group I-A)   1) Like alkali metals hydrogen has one electron in its valency shell.   Explanation   H (Z=1): K1Li (Z=3): K2, L1Na (Z=11): K2, L8, M1   (2) Valance shell electronic configuration of hydrogen and alkali metal is same.   Explanation   H (Z=1): 1S1Na (Z=11): 1S2,2S2,2P6,3S1    3) Both hydrogen an alkali metals are good reducing agents.   4) Like alkali metals hydrogen can also form halides.   Explanation:   Hydrogen:HCl, HI.I-A:NaCl, KBr.   5) Halides of alkali metals and hydrogen ionized in similar way in aqueous solution.   Explanation:HCl (aq) è H+(aq) + Cl-(aq)NaCl(aq) è Na+(aq) + Cl-(aq)   6) Like alkali metals hydrogen can also form compounds with non-metals.   Explanation:I-A:Na2SHydrogen:H2S[S and Cl are non-metals]   DIFFERENCES :-   1) Hydrogen is a non-metal where as elements of I-A are metals.2) Hydrogen can form both covalent and ionic compounds. But alkali metals only form ionic compounds.3) Hydrogen cannot lose its valence electron.4) Hydrogen is a gas at room temperature but alkali metals are solids.5) Unlike Na+ or K+ hydrogen ion (H+) is unstable in water.   Explanation:   H+ + H2O è H3O+   6) I.P. Of hydrogen is very high as compared to alkali metals.   ExplanationI.P. Of hydrogen is 313 Kcal per mole.I.P. Of alkali metals max. Is 147 Kcal per mole.   Resemblance of Hydrogen with Carbon Family (IV-A)1) Valance shell of hydrogen is half-filled like the elements of group IV-A.Explanation:   H (Z=1) :  Capacity of K-Shell =2 , no. Of electrons = 1 , % = 50%   C(z=6) :   Capacity of L-Shell = 8 , no. Of electrons = 4 , % = 50%2) I.P. And E.A. Of hydrogen and carbon are comparable.3) E.N. Of H and Carbon family are almost similar. [H = 2.1, C = 2.5 , Si= 2.4]Explanation DIFFERENCES 1) Carbon is tetravalent but Hydrogen is a mono-valent.2) Hydrogen is a gas at room temperature but elements of group IV-A are solids.3) Boiling and melting points of hydrogen is very less than that of the elements of group IV-A.Resemblance Of Hydrogen With Halogens1) Both Hydrogen and Halogens require one electron to complete their valence shell.2) Both hydrogen and Halogens are non-metals(Except iodine which has partial metallic character).3) Both hydrogen and Halogens acts as negative ions when combined with metals. 4) Their molecules are diatomic.5) Like Halogens, hydrogen can also form both ionic and covalent bond.ExplanationHydrogen:NaH (ionic), CH4 (Covalent)Halogens:NaCl (ionic), HCl 6) Both H and Halogens form compound with metals and non-metals.ExplanationHydrogen :H2S [S=non-metal]Halogens : HCl [H = non-metal]DIFFERENCES 1) Hydrogen has one electron in valence shell while Halogens has seven electrons.2) Electronic configuration of H = 1S1,Valence shell electronic configuration of Halogens = nS2, nS53) Unlike X- ion, H- ion is unstable in water and reacts in the following manner.ExplanationH- + H2O èH2+ OH-

Although it is not a metal but in most of the modern versions of Periodic Table, hydrogen is placed at the top of the group IA. This is because of the fact that some of the properties of hydrogen resemble with those of alkali metals. Like alkali metals hydrogen atom has one electron in its sub shell which it can lose to form H+. Both hydrogen and alkali metals have a strong tendency to combine with electronegative elements such as halogens. Similar to alkali metals hydrogen also forms ionic compounds, which dissociate in water. However, hydrogen is also markedly different from alkali metals. For example, hydrogen is a non-metal in true sense. It does not lose electron as easily as most of the alkali metals do. Unlike alkali metals molecular hydrogen exists in open atmosphere.

Hydrogen resembles halogens in certain respects and can be placed at the top of VIIA group in the Periodic Table. Hydrogen is a gas like most of the halogens and is stable in diatomic form such as F2, C12 and Br2. As required by halogens, hydrogen also needs, one electron to complete its last shell. By accepting one electron hydrogen forms H" (Hydride ion) similar to F", Cl and Br". Both hydrogen and halogens form stable ionic compounds with alkali metals. However, hydrogen differs from halogens as well. By losing its only electron, hydrogen forms H+ but halogens do not form positive ions. Combining with oxygen, hydrogen forms very stable oxides while halogens lack this property.
Some of the characteristic properties of hydrogen also resemble with those of group IVA elements such as C and Si, etc. For example, valence shell of hydrogen is half filled like those of group IV elements. Both, hydrogen and group IV elements

combine with other elements through covalent bonding. Like carbon, hydrogen also possesses remarkable reducing properties.
Hydrogen also shows marked differences with carbon and rest of the group members. For example, carbon and silicon form long chain compounds when their atoms combine with each other, while hydrogen do not form such compounds. Similarly carbon can simultaneously form bonds with more than one elements whereas hydrogen due to having only one electron can combine with only one element at a time.

Some of the properties of hydrogen are similar to those of the elements of certain groups, as discussed above, but this is a fact that hydrogen is a unique element whose properties do not match exactly with any of the groups in the Periodic Table. However due to partial resemblance in properties with alkali metals and monovalent nature, hydrogen is usually placed at the top of elements in group IA.