The key points of group-15 elements
In this article, the key points of group-15 elements, we are gonna learn about some basic and important points or properties of group-15 elements of periodic table.
Before starting, we would like to tell you about p-block. It is an area in the periodic table containing column from 3A to column 8A except for Helium.
There are 35 p-block elements and every one of them has valence electrons in p-orbitals.
- p-block elements are placed in group 13 to 18 of the periodic table. Their valence shell electronic configuration is ns^2np^1-6 (except He which has 1s^2 configuration).
- The first member of each of the groups 13-17 of the p-block elements differs in many respects from the rest of the members of their respective groups. This anomalous behavior is due to small size, high electronegativity and inability to expand its octet due to the absence of d-orbitals in the valence shell.
- Group-15 includes N, P, As, Sb and Bi. Nitrogen and Phosphorus are non-metals, arsenic and antimony are metalloids and bismuth is a typical metal. their valence shell electronic configuration is ns^2np^3.
- Ionisation enthalpies decrease down the group due to a gradual increase in atomic size. Ionisation enthalpies of group 15 elements are greater than that of group 14 and group 16 elements in the corresponding periods due to extra stable hall-filled p-orbitals.
- Electronegativity decreases down the group with increasing atomic size.
- Dinitrogen is a diatomic gaseous molecule with a triple bond between the two atoms. Its bond enthalpy is very high. Other members are solids. They do not form pπ-pπ multiple-bonds, they form single bonds as P-P, As-As, etc.
- N-N single bond is weaker than P-P single bond due to the greater repulsion of non-bonding electrons (due to small bond length). As a result, catenation tendency is weaker in nitrogen than phosphorus.
- Common oxidation states of these elements are -3, =3 and =5. The tendency to show -3 oxidation state decreases down the group due to increase in size and metallic character. The stability of +5 oxidation state decreases and that of +3 increases down the group due to inert pair effect.
- Group 15 elements form MH3 type hybrids. Stability, HMH BOND angle, bond dissociation enthalpy, and basicity decrease from NH3 to BiH3, but boiling points and reducing characters increases from PH3 to BiH3. However, the boiling point of NH3 is extraordinarily high due to H-bonding.
- Nitrogen does not form pentahalides because it does not have d-orbitals to expand its covalence beyond four.
- In case of nitrogen, all oxidation states from +1 to +4 and in case of phosphorus nearly all intermediate oxidation states disproportionately in acid and in alkali solutions.
- Dinitrogen is rather inert at room temperature due to the high bond enthalpy of N≡N bond.
- On small scale, NH3 is obtained from ammonium salts, which decompose when treated with caustic soda or lime and on large scale it is manufactured by Harber’s process NH3 acts a Lewis base because it can donate one lone pair of electrons.
- N2O and NO are neutral oxides, while other oxides of nitrogen are acidic. NO2 dimerize because it contains an odd number of valence electrons. The covalence of nitrogen in N2O5 is 4.
- Nitric acid on large scale is prepared by Ostwald’s process. This method is based upon catalytic oxidation of NH3 by atmospheric oxygen. It is a strong oxidizing agent and attacks most metals except noble metals (Au and Pt).
- The familiar brown ring test for nitrates depends on the ability of Fe^2+ to reduce nitrates to nitric oxide which on reaction with Fe^2+ ions from a brown coloured complex.
- Except for nitrogen, all the elements show allotropy. White phosphorus is more reactive than red phosphorus due to angular strain in the P4 molecule. White P consists of the discrete tetrahedral P4 molecule, while red P consists of polymeric chains of P4 tetrahedra.
- Phosphorus like ammonia is weakly basic in nature and gives phosphonium compounds with acids. Bond angle in PH4^+ is higher than that in PH3 because LP-bp repulsion in PH3 reduces the bond angle to less than 109°28′.
- PCl5 in gaseous and liquid phase has a trigonal bipyramidal structure. The three equatorial P-Cl bonds are equivalent, while the two axial bonds are longer than equatorial bonds. In the solid state, PCl5 exists as an ionic solids[PCl5]^+[PCl6]^- in which cation is tetrahedral and the anion is octahedral.
- Phosphorus forms a number of oxoacids. Their basicity is equal to the number of P-OH bonds in the molecule. In oxoacids, phosphorus is tetrahedrally surrounded by other atoms. All these oxoacids contain at least one P=O and one P-OH bond.
- Hypophosphorous acid, H3PO2 is a good reducing agent.