Question

Which is the first element of the periodic table $ ? $

Answer 1

Hint :Periodic table is a tabular display of chemical elements that are naturally occurring or are man-made. Elements are arranged periodically on the basis of atomic number, electronic configuration and chemical properties. The modern periodic table that we use today was proposed by Dmitri Mendeleev and is thus known as Mendeleev’s periodic table.

Complete Step By Step Answer:
The modern periodic table consists of $ 118 $ elements of which $ 94 $ are naturally occurring, the rest are man-made. Hydrogen (H) is the first element of the periodic table with atomic number $ 1 $ . Its atomic weight is 1.008 u and is the lightest element in the periodic table. It is a colourless, odourless, tasteless and inflammable diatomic gas that exists as $ {H_2} $ in the atmosphere.
A hydrogen atom consists of a single proton in its nucleus and an electron in its outermost shell. It does not have any neutrons. The electronic configuration of H is $ 1{s^1} $ . Two hydrogen atoms share their outer electrons to form a covalent bond to attain a stable $ 1{s^2} $ configuration and exist as $ {H_2} $ . The position of hydrogen in the periodic table is a matter of discussion. Due to its $ n{s^1} $ configuration, it resembles the alkali metals. But, the ionisation energy is very high and comparable with the halogens. Like halogens, it is non-metal and accepts an electron to complete its valence shell. Considering many other factors like melting and boiling point, reactivity towards metals and non-metals , hydrogen is placed under Group $ 1 $ and period $ 1 $ of the periodic table.

Note :
Hydrogen bond is an electrostatic attraction between a hydrogen atom and any electronegative elements like N,F,O . Though weaker than fully covalent or ionic bonds, it is inevitable in forming the structure of DNA and proteins. Also, hydrogen bonds account for the stability, structure and physical or chemical properties (like high boiling points) of many organic and inorganic compounds.