[Explained] Why is Hydrogen Placed in Group 1 of the Periodic Table

 Hydrogen is the first element in the periodic table and it has the atomic number 1 as it has only one electron in its valence shell.

Since a long time, the correct position of hydrogen in the periodic table has been a matter of debate. And the reason for this is primarily the fact that hydrogen resembles the properties of two groups of the periodic table. Namely, the Group 1(A) commonly known as the Alkali Metals and Group 17 or Group VIIA which is commonly known as the Halogens.

The electron configuration of hydrogen and the alkali metals is one of the main reasons why hydrogen is placed in group 1 along with other alkali metals.

Hydrogen, Lithium, Sodium, Potassium, Rubidium, Cesium all have a single electron in their outermost orbits. This can be seen in the table below.

What this means is that hydrogen along with the other alkali metals has one electron in their valency shell and therefore all of them have one valence electron.

All alkali metals, including hydrogen have the valency 1.

All of the alkali metals form cation which is a positively charged ion by losing an electron. They all have a tendency to lose electron and thus have a low ionization energy and it keeps on decreasing down the group.

Alkali metals and hydrogen exhibit reducing power and act as good reducing agents.

Hydrogen burns in oxygen to form water, which is essentially its oxide.

A fun fact to note here is that oxygen burns with a pop sound.

Alkali metals also burn when heated in oxygen. Lithium forms monoxide, sodium forms peroxide, whereas potassium, rubidium, and cesium form superoxides having a general formula MO2.

Alkali metals are very reactive in the presence of air. They are so reactive that they get rapidly tarnished when exposed to air. This is due to the formation of oxides and hydroxides, and finally, carbonates, on their surface.

And because of this nature of the alkali metals they are always stored in inert organic solvent such as kerosene oil, under mineral oil or an inert gas such as argon.

Alkali metals and hydrogen also forms their respective compounds after reacting with non-metals such as oxygen, sulfur and chlorine.

Hydrogen and the halogens have one less electron than the nearest noble gas. This can be seen in the table given below.

All the halogens namely, Fluorine, Chlorine, Bromine, Iodine, Astatine and Hydrogen have the valency of 1. 

Therefore, all of them accept an electron to attain the electron configuration of the nearest noble gas. Hydrogen accepts one electron to attain the electron configuration of Helium, Fluorine accepts one electron to attain the electron configuration of Neon, Chlorine accepts one electron to attain the electron configuration of Argon, Bromine accepts one electron to attain the electron configuration of Krypton and so on.

All the halogens show a tendency to form anions, negatively charged ions as they are one electron short of the nearest noble gas configuration. This means they have high electronegativity. 

Both halogens and hydrogen are non metals. They show electronegative character. 

Like Fluorine and Chlorine which are the first two elements of the group 17 Hydrogen is also a gas.

Hydrogen as well as halogens exist in the form of diatomic molecules.

Even though Hydrogen has few similarities in character of Alkali metals and Halogens, there are also few characteristics that do not have any similarity with either of them.

Hydrogen atom has only one shell but alkali metals and halogens have more than one shells.

Oxide of Hydrogen is a neutral oxide. Oxides of halogens are mostly acidic in nature, while oxides of alkali metals are basic in nature.