1. PREPARED BY  MR. AMULYA KUMAR SAMAL  PGT(CHEMISTRY)  KENDRIYA VIDYALAYA NO-2,CRPF,BHUBANESWAR  PHONE NO.07381884606  E-mail-aksamal74@gmail.com  MR. AMULYA KUMAR SAMAL  PGT(CHEMISTRY)  KENDRIYA VIDYALAYA NO-2,CRPF,BHUBANESWAR  PHONE NO.07381884606  E-mail-aksamal74@gmail.com Group 15 Elements

2. OBJECTIVES:- After studying this unit, the students will be able to : 1.appreciate general trends in the chemistry of elements of groups 15 2.describe the properties of group-15. 3.Give answer the reasoning question. After studying this unit, the students will be able to : 1.appreciate general trends in the chemistry of elements of groups 15 2.describe the properties of group-15. 3.Give answer the reasoning question.

3. The p-block elements  The p-block elements are placed in groups 13 to 18 of the periodic table.  Their valence shell electronic configuration is ns 2 np 1–6 (except He which has 1s 2 configuration)

4. Group 15 Elements  Nitrogen(N)  Phosphorus(P)  Arsenic(As)  Antimony(Sb)  Bismuth(Bi) Metalloids Typical Metal Non Metals

5. Trends in properties  Electronic Configuration The s orbital in these elements is completely filled and p orbitals are half-filled, making their electronic configuration extra stable. The valence shell electronic configuration of these elements is ns 2 np 3.

6.  Atomic and Ionic Radii N P As Sb Bi considerable increase small increase due to the presence of completely filled d and/or f orbitals in heavier members.sss

7.  Ionisation Enthalpy Δ i H N P As G-14 Bi Δ i H Decreases. Sb G-15 Δ i H Increases Because of the extra stable half-filled p orbitals electronic configuration and smaller size Due to gradual increase in atomic size Δ iH 1 < Δ iH 2 < Δ iH 3

8.  Electronegativity N P As Bi E.N Decreases. Sb Due to gradual increase in atomic size 3.0 2.1 2.0 1.9

9. Physical Properties  All the elements of this group are polyatomic.  Dinitrogen is a diatomic gas while all others are solids.  Metallic character increases down the group.  The b.p, in general, increase from top to bottom in the group but the m.p increases up to As and then decreases up to Bi.  Except nitrogen, all the elements show allotropy.

10. Chemical Properties Oxidation states and trends in chemical reactivity The common o.s of these elements are –3, +3 and +5. Group-15 Tendency to exhibit –3 o.s decreases due to increase in size and metallic character. The stability of +5 o.s decreases and that of +3 state increases (due to inert pair effect) down the group.

11. Nitrogen exhibits + 1, + 2, + 4 O.S also when it reacts with oxygen. In the case of nitrogen, all O.S from +1 to +4 tend to disproportionate in acid solution. For example, 3HNO 2 → HNO 3 + H 2 O + 2NO Similarly, in case of phosphorus nearly all intermediate O.S disproportionate into +5 and –3 both in alkali and acid. Nitrogen is restricted to a maximum covalency of 4. Because only four (one s and three p) orbitals are available for bonding. The heavier elements have vacant d orbitals in the outermost shell which can be used for bonding (covalency) and hence, expand their covalence as in PF 6 –.

12. Anomalous properties of nitrogen Reasons: 1.Its small size 2.high electronegativity 3.high ionisation enthalpy 4.non-availability of d orbitals.

13. Some anomalous properties of Nitrogen 1.State: Nitrogen is a gas whereas the others elements are solids and have allotropic forms. 2.Atomicity: Dinitrogen is diatomic and involves triply bonded nitrogen N N. Other members have tetra-atomic molecules such P 4,As 4,Sb 4 and complicated arrangements such as red and black phosphrous.

14. 3.Ability to form pπ -pπ multiple bonds: Nitrogen has unique ability to form pπ -pπ multiple bonds with itself and with other elements having small size and high electronegativity (e.g., C, O). Heavier elements of this group do not form pπ -pπ bonds as their atomic orbitals are so large and diffuse that they cannot have effective overlapping. Thus, nitrogen exists as a diatomic molecule with a triple bond (one s and two p) between the two atoms. Consequently, its bond enthalpy (941.4 kJ mol–1) is very high. On the contrary, phosphorus, arsenic and antimony form single bonds as P–P, As–As and Sb–Sb while bismuth forms metallic bonds in elemental state.

15. 4.Catenation: The single N–N bond is weaker than the single P–P bond because of high interelectronic repulsion of the non- bonding electrons, owing to the small bond length. As a result the catenation tendency is weaker in Nitrogen. 5) Reactivity towards hydrogen:

16. The hydrides are Lewis bases due to the presence of lone electron pair on central atom. The basic strength decreases in the order:NH 3 >PH 3 >AsH 3 >SbH 3 >BiH 3 The thermal stabilities decrease from NH 3 towards BiH 3 as the thermal stability is inversely proportional to the M-H bond length.

17. The reducing nature of the hydrides is expressed in terms hydrogen giving tendency and it is found to increase from NH 3 to BiH 3 The boiling point of ammonia is more than that of phosphine (and also AsH 3 ) because of the presence of intermolecular hydrogen bonding in the molecules.

18. (6) Reactivity towards oxygen: All these elements form two types of oxides: E 2 O 3 and E 2 O 5. The oxide in the higher oxidation state of the element is more acidic than that of lower oxidation state. Their acidic character decreases down the group. The oxides of the type E 2 O 3 of nitrogen and phosphorus are purely acidic,that of arsenic and antimony amphoteric and those of bismuth predominantly basic.

20. Self Assesment EXAMINATION DECODED Important question with answer Give Reason for each of the following :- Q.1# NCl 5 does not exist but NCl 3 exits BUT both PCl 3 & PCl 5 exists. Ans:-Due to absence of vacant d-orbitals in N, it cannot extend its co- valency. Q.2# PCl 5 is ionic in nature in the solid state. OR, Solid PCl 5 exists as an ionic solid. Ans:- Due to unequal bond length of equatorial and axial bond. The close range in solid state makes it stabilized by transferring one Cl- from one PCl 5 to other PCl 5 and exist as ionic solid, [PCl 4 ] + [PCl 6 ] ־. Q.3# NH 3 acts as ligand or good complexing agent.OR, NH3 has higher H + affinity than PH 3. Ans:-Due to presence of lone pair electrons.

21. (4)Arrange the following in increasing order of the property indicated: NH 3, PH 3, AsH 3, SbH 3, BiH 3 (Thermal stability) NH 3, PH 3, AsH 3, SbH 3, BiH 3 (Bond dissociation enthalpy) NH 3, PH 3, AsH 3, SbH 3, BiH 3 (Reducing character) NH 3, PH 3, AsH 3, SbH 3, BiH 3 (Basic character) Ans: (a)NH 3 > PH 3 > AsH 3 >SbH 3 >BiH 3 (b) NH 3 < PH 3 < AsH 3 <SbH 3 <BiH 3 (c) NH 3 < PH 3 < AsH 3 <SbH 3 <BiH 3 (d) NH 3 > PH 3 > AsH 3 >SbH 3 >BiH 3