Hydrogen is the first element in the periodic table. Hydrogen is placed in no specific group due to its property of gaining electron (When `H^-` is formed) and also losing electron ('When `H^(+)` is formed).
(i) Hydrogen is placed in `text(Group)` `I` (Alkali metals) as,
(a) It has one electron in its (Outer) Shell `1s^(1)` like other alkali metals which have (inert gas) `ns^1` configuration.
(b) It forms monovalent `H^+` ion like `Li^+, Na^+.....`
(c) Its valency is also `1`.
(d) Its oxide `(H_2O)` is stable as `Li_2O, Na_2O`.
(e) It is a good reducing agent (In atomic as well as molecular state) like `Na, Li....`
(ii) Hydrogen also resembles halogens (`text(Group) VIII A`) as,
(a) It is also diatomic `(H_2)` llike `F_2, Cl_2`.
(b) It also form anion `H^-` like `F^-, Cl^-`........... by gain of one electron.
(c) `H^-` has stable inert gas `(He)` configuration as `CH_4`, `C_2H_6`, like halogens `CCl_4`, `SF_2Cl_2` etc.
(d) `H` is one electron short of duplet (Stable configuration ) like `F`, `Cl....` which are also one electron deficient than octet, `F-2s^2 2p^5`; `Cl- 3s^2 3 p^5`.
(e) (`text(IE)`) of `H(1312kJmol^-1)` is of the same order as that of halogens.
(iii) (`IE` ) of `H` is very high in comparison with alkali metals. Also size of `H^(+)` is very small compared to that of alkali metal ion. `H` forms stable hydride only with strongly electropositive metals due to smaller value of its electron affinity `(72.8 KJ mol^(-1))`
(iv) In view of the anomalous behavior of hydrogen, it is difficult to assign any definite position to it in the periodic table. Hence it is customary to place it in group `I` (Along with alkali metals) as well as in group `VII` (Along with halogens).
Hydrogen is the first element in the periodic table. Hydrogen is placed in no specific group due to its property of gaining electron (When `H^-` is formed) and also losing electron ('When `H^(+)` is formed).
(i) Hydrogen is placed in `text(Group)` `I` (Alkali metals) as,
(a) It has one electron in its (Outer) Shell `1s^(1)` like other alkali metals which have (inert gas) `ns^1` configuration.
(b) It forms monovalent `H^+` ion like `Li^+, Na^+.....`
(c) Its valency is also `1`.
(d) Its oxide `(H_2O)` is stable as `Li_2O, Na_2O`.
(e) It is a good reducing agent (In atomic as well as molecular state) like `Na, Li....`
(ii) Hydrogen also resembles halogens (`text(Group) VIII A`) as,
(a) It is also diatomic `(H_2)` llike `F_2, Cl_2`.
(b) It also form anion `H^-` like `F^-, Cl^-`........... by gain of one electron.
(c) `H^-` has stable inert gas `(He)` configuration as `CH_4`, `C_2H_6`, like halogens `CCl_4`, `SF_2Cl_2` etc.
(d) `H` is one electron short of duplet (Stable configuration ) like `F`, `Cl....` which are also one electron deficient than octet, `F-2s^2 2p^5`; `Cl- 3s^2 3 p^5`.
(e) (`text(IE)`) of `H(1312kJmol^-1)` is of the same order as that of halogens.
(iii) (`IE` ) of `H` is very high in comparison with alkali metals. Also size of `H^(+)` is very small compared to that of alkali metal ion. `H` forms stable hydride only with strongly electropositive metals due to smaller value of its electron affinity `(72.8 KJ mol^(-1))`
(iv) In view of the anomalous behavior of hydrogen, it is difficult to assign any definite position to it in the periodic table. Hence it is customary to place it in group `I` (Along with alkali metals) as well as in group `VII` (Along with halogens).