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Discuss the trends in chemical reactivity of group 15 elements. |
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Answer» <P> Solution :Nitrogen gas exists as diatomic MOLECULE. Dut to the presence of triple bond between Base N - Atoms bond dissociation energy is HIGH (941.4 KJ / mol). Hence nitrogen is inert and unreactive.Phosphorus is a tetra atomic molecule and P-P single bond is weaker than `N-=N`. P - P bond dissociation energy U 213 KJ/mole. Hence phosphorus is more reactive than Nitrogen. Explanation : `to` The single N-N bond is weaker than the single P-P bond due to high inter electronic repulsion of the non-bonding electrons in `N_(2)` because of small bond length. There fore the catenation property is weaker in nitrogen as compound to phosphorares. `R_(3)` P = O exist but `R_(3)N` = O does not. Explanation : `to` Nitrogen does not form `d pi-P pi` multiple bond with oxygen because of lack of d - orbitals in Nitrogen atom. But in case of `R_(3)N=0` the value of nitrogen should be 5. So these compounds do not exist where as in case of 'P' atom d-orbitals are available. So P-atom can able to form `d pi-P pi` multiple bonds hence `R_(3)P=0` exist. i) Reactivity towards hydrogen : Group - 15 elements forms `"EH"_(3)` type hydrides (E = Group - 15 elements) Eg : `"PH"_(3),"NH"_(3),"AsH"_(3),"BiH"_(3),"SbH"_(3)`. `to` Among above hydrides `NH_(3)` is mild reducing agent while `"BiH"_(3)` is strong reducing agent. `to` Stability of hydrides DECREASES from `"NH"_(3)` to `"BiH"_(3)`. `to` Basicity of hydrides decreases as follows. `"NH"_(3)gt"PH"_(3)gt"AsH"_(3)gt"SbH"_(3)gt"BiH"_(3)`. ii) Reactivity towards Oxygen : These forms two types of oxides `E_(2)O_(3)` and `E_(2)O_(5)`. Eg : `P_(2)O_(3),N_(2)O_(5),N_(2)O_(3),P_(2)O_(5)`. `to` Acidic character of oxides decrease down the group. `to E_(2)O_(3)` of N and P are acidic, As and Sb are amphoteric while 'Bi' is basic. iii) Reactivity towards halogens : These elements forms two types of halides `"EX"_(3)" and EX"_(5)`. `to` 'N' - does not form penta halides due to lack of the d-orbitals. `to` Penta halides are more covalent than TRI halides because the elements in higher oxidation state have more polarising power. iv) Reactivity towards metals : All these elements react with metals to form their binary compounds containing - 3 oxidation state. Eg : `"Ca"_(3)"N"_(2),"Ca"_(3)"P"_(2)` etc. |
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