Hydrogen is the first element in the periodic table and is the smallest among all elements present on the table. Its atomic number is 1 which indicates that it has only one electron that is orbiting in its valance shell. It has one shell only and is the lightest element present on the periodic table.
In the modern periodic table, the position of the elements is largely dependent on their electronic configuration and the electronic configuration of hydrogen is 1. If hydrogen gets rid of its electron then it can attain the electronic configuration of the noble gasses. This character of the hydrogen element is similar to that of the alkali metals. But if hydrogen gains the one electron then its configuration will be similar to that of halogens. So, hydrogen has a resemblance to the elements of the group I-A, IV-A, and VII-A in few respects.
However, the properties of hydrogen do not completely match any of these groups. Due to this reason, the position of hydrogen is still considered as undecided as hydrogen behaves like halogens as well as like alkali metals. It occurs as a diatomic molecule in nature like halogens and reacts with the non-metals and metals leading to the formation of covalent bonds. Like other alkali metals, hydrogen is a good reducing agent. Just like alkali metals, hydrogen reacts with oxygen, halogens, and Sulphur to make the compounds having the same formula.
Similarities of Hydrogen to Metals
Hydrogen has many similarities to the alkali metals which are the elements placed in the group I-A. This is one of the significant factors that dictate the hydrogen’s position in the periodic table. Like the alkali metals when hydrogen combines with the electronegative elements, it forms the halides.
Similarities of Hydrogen to the Halogens
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.
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.
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.