Position of Hydrogen in Periodic Table

Hydrogen is the first element in modern periodic table. Since hydrogen has only one electron in its valance shell, it has equal potential to gain or lose electron for attaining the stable configuration state. It has unique physical structure and shows anomalous behaviour.
Hydrogen either can gain electron to become and hydride ion or lose electron to become an hydrogen ion as shown below:

$$\ce{H – e^- -> $\underset{\text{Hydrogen ion}}{\ce{H^+}}$}$$
$$\ce{H + e^- -> $\underset{\text{Hydride ion}}{\ce{H^-}}$}$$

As hydrogen resembles to alkali as well as halogen in the periodic table, the position of hydrogen is still controversial in Mendeleev’s as well as modern periodic table.

Some of the similarities with alkalis are:

1. Electronic configuration: Both hydrogen and alkali metals have one electron in valence shell. So they have same outermost electronic configuration.

2. Non Metallic Character: Like alkali metals, hydrogen loses its one electron to form hydrogen ion.
$$\ce{H-> H^+ + e^-}$$
$$\ce{Li-> Li^+ + e^-}$$

3. Oxidation state and valency: Both hydrogen and alkali metals have oxidation state +1 and valency equals to 1.

4. Electrolysis: Hydrogen and alkali metals are liberated at cathode when their compounds are electrolyzed.

5. Affinity for non metals: Like alkali metals, hydrogen combines with non metals like halogen, oxygen and sulphur to form their respective halides, oxides, sulphide etc.

6. Reducing nature: Alkali metals and halogen are strong reducing agent.
$$\ce{CuO + H2->[\Delta]Cu + H2O}$$
$$\ce{CuO + Na->[\Delta]Cu + NaO}$$


Similarities with halogens:

1. Electronic configuration: Both hydrogen and halogens have one electron less to acquire stable configuration state. So, both of them are one electron deficient elements.

2. Non metallic characters: Like halogens, hydrogen is also shows non metallic characters.


3. Atomicity: Like halogens, hydrogen exists in diatomic state.

4. Physical state: Like halogen, hydrogen is a gas.

5. Ionization energy: The ionization energy of hydrogen is similar to that of halogens.

6. Mutual replacement: Hydrogen replaces hydrogen from its covalent compounds and vice versa .This means hydrogen can be used instead of halogen and halogen can be used instead of hydrogen in some reactions.

7. Electrolysis: In the electrolysis of metal halides like NaCl, HBr etc. halogen and hydrogen both are liberated at anode.

8. Oxidation state: Both halogens and hydrogen have oxidation state -1.

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2 Responses to “Position of Hydrogen in Periodic Table”

  1. santosh kumar

    why molecules moves are atmossphare

  2. santosh kumar

    why molecules moves are atmossphare?