Hydrogen

Hydrogen() is the 1st element in the periodic table according to its atomic number 1. It's the lightest element, at just a little over 1u. It makes up about 75% of the entire universe.. 
Hydrogen has the simplest atomic structure among all the elements around us in Nature. In atomic form it consists of one proton and one electron. However, in elemental form it exists as a diatomic(H2) gaseous molecule and is called dihydrogen.
==Position in Periodic Table==
Hydrogen, as we know, is the first element in the periodic table. Its placement in the periodic table, however, has been a subject of debate in the past. The elements are arranged in the periodic table according to their electronic configurations. Hydrogen has the electronic configuration of 1s1. On one hand, its electronic configuration is similar to the outer electronic configuration of alkali metals, which belong to the first group of the periodic table. On the other hand, like halogens, it is one electron short to the corresponding noble gas configuration of helium(1s2).
Hydrogen has many similarities with alkali metals and haligens(See Properties section below.). Inspite of that, it differs from them as well. Loss of the electron from hydrogen atom results in nucleus(H+) of ~1.5×10pm size. This is extremely small as compared to normal atomic and ionic sizes of 50pm to 200pm and thus H+ does not exist in free state and combines with other elements to form hydrides and many different compounds. Due to its uniqueness, hydrogen is placed separate from all the elements in a periodic table. Yet some periodic tables continue to keep hydrogen in the first period(Which is acceptable), but keeping hydrogen in group 1 is simply recognised as "against standards and rules" or "Scientifically incorrect".
==Properties==
Hydrogen has the properties of both alkali metals and halogens. Like alkali metals, hydrogen forms oxides, halides and sulphides. But it does not possess metallic characteristics, unlike alkali metals, under normal conditions and has very high ionization enthalpy. In terms of its ionization enthalpy, hydrogen resembles more with halogens, ΔiH of Li is 520 kJ/mol, F is 1680 kJ/mol and that of H is 1312 kJ/mol. Like halogens, it forms a diatomic molecule, combines with elements to form hydrides and a large number of covalent compounds.
Category:Element
Category:Non Metal