B.sc 1st year Book
(Page 13)

Group VA (15) Elements: N, P, As, Sb, Bi Nitrogen family

Group 15 of the periodic table includes the elements nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). Like other groups, these elements also show gradation in properties, but the properties of nitrogen differ markedly from other members. It is mainly due to the small size and absence of d-orbitals in nitrogen. (Nitrogen family)

1- Electronic configuration of nitrogen family :

The outer electronic configuration of VA group elements is ns2np3 in which all the p-orbitals are half-filled. The electronic configurations of VA groups are given in the following table (4.9).

Table 4.9: Electronic configuration of VA elements

Element Symbol Atomic No. Electronic configuration with an inert gas core
Nitrogen N 7 [He]2 s2,2p3
Phosphorus P 15 [Ne]3 s2,3p3
Arsenic As 33 [Ar]3 d10,4 s2,4p3
Antimony Sb 51 [Kr]4 d10,5 s2,5p3
Bismuth Bi 83 [Xe]4ff14,5 d10,6 s2,6p3

2- Metallic property of nitrogen family:

In group VA, Nitrogen and phosphorus are nonmetals, arsenic and antimony are semi-metals or metalloids and bismuth is metal. Thus, on going down the group metallic character increases from N to Bi.

3- Atomic and Ionic radii of the nitrogen family:

With the increase of atomic number, the value of n and also the atomic size increase. This is due to the increase in the number of inner orbital shells. Thus, nitrogen has the smallest and bismuth has the largest size. A similar sequence is observed in ionic size, as shown in table (4.10).

4- Ionization potential and electronegativity of nitrogen family :

These elements have small sizes, hence their ionization potential and electronegativity are comparatively high. Besides, due to their half-filled arrangement, they acquire so much stability. So they have ionization potential values that are higher than the next VIIA group elements. In the group, the ionization potential and electronegativity values of N are highest and the decrease on moving from N to B is shown in table(4.10).
However, E. A. values of these elements have no regular trend in the group.
Table 4.10: Physical properties of V A elements

7- Oxidation states and valency:

As these elements have five electrons in their outermost school, their maximum oxidation state care is +5 in the compounds. Their p-orbitals have 3 electrons less than the noble gas configuration, hence they can also show a – 3 oxidation state. Thus, in their compounds, the oxidation states vary between −3 to +5. In the normal state, these elements form 3 covalent bonds in their compounds. Except for Nitrogen, and other elements of the group. VA has empty nd-orbitals, with the transference of one ns-electron to nd-orbital, we have five sp 3 d bonding orbitals. Thus, the maximum covalency of these elements is five.

8- Catenation property:

Although this is the characteristic property of carbon, the elements of this group which lie close to carbon in the periodic table also show this property to some extent. Nitrogen which has the minimum for its N−N bond energy (163.1KJmol−1 ) shows this property to the maximum extent. Thus, N atoms can form many compounds which contain straight chains of two or more N-atoms, for example.

Nitrogen which has the minimum for its N−N bond energy (163.1KJmol−1 )

9- Allotropy :

In group VA, phosphorus exhibits allotropy. The most common allotrope is white phosphorus, It is soft as wax and colorless. It metts at 44.25∘C and density are 1.8232 g cm−3 lt is soluble in liquid CS2 and benzene. it is highly reactive/sensible and spontaneously ignites in air. It glows in dark and this property gives the elements its name phosphorus (Greek for light bringing) It consists of discrete P4 molecules. In which the four P-atoms lie at the corner of a regular tetrahedron and each p-atom is linked to the other three P-atoms by normal covalent bonds(see fig. 4.14),regular tetrahedron and each p-atom is linked to other three P-atoms by normal covalent bonds atoms rearrange. White phosphorus does not conduct electric current. It is highly toxic. When white phosphorus is heated at −277∘C in an inert atmosphere for several days it get converted into red phosphorus which has a higher m.p. (597∘C) and greater density (∼2−16gcm−3) than white phosphorus. In this material, each phosphorus atom is linked with three others put in such a way that they form an irregular network as shown in figure 4.15.
Fig. 4.15: Structure of Red Phosphorus (P4)in
Red phosphorus is an amorphous solid, It is less reactive than white phosphorus. It is non toxic. Thermodynamically, the most stable form of phosphorus is black phosphorus. It is obtained by heating white phosphorus at 200∘C to a pressure of 1200MPa. If extreme pressure (10,000MPa) is used, a short impact is enough to convert white phosphorus quantitatively to black. It is denser (density =2.69gcm−3) than white phosphorus (density = 1.82gcm−3) ar violet phosphorus (density =2.36gcm−3 ). Black phosphorus (orthorhombic) has a parallel, puckered double layers structure as shown in figure (4.16).
but phosphorus is nom concrete and A temperature. However, its band gap is relatively narrow. It exists up to a temperature of 550∘C. But above that, it is converted to violet phosphorus. The violet phosphorus is formed by heating white phosphorus for one or two weeks to a temperature above 550∘C. It is a transparent crystal plate with a violet tinged at the edge. It has also a double-layered structure. Which consists of parallel, pentagonal tubes of phosphorus atoms.

10- Hydrides :

All elements of group VA form gaseous hydrides of the typeMH3. The stability of the hydrides decreases sharply/clearly on moving down the group. The ease of hydrolysis also increases in the same order with an increase in atomic number. Except for NH3, all the hydrides are strong reducing agents and react with metal ions (Ag’, Cu+) to give phosphides, arsenides, or antimonides.

Fig. 4.16: Structure of double-layer orthorhombic black phosphorus. The boldface letters indicate atoms above the plane of the paper while the regular type indicates atoms below the plane of the paper.
NH3 is a strong Lewis base due to the presence of a lone pair of electrons. It has also a great tendency to form H-bond. PH3 is a weaker base than ammonia whereas AsH3, SbH3, and BiH 3 do not show any basic properties. It is because in these hydrides M has an empty nd-orbital. In these hydrides, M undergoes sp3 hybridization. They have pyramidal shapes but their HMH bond angles are different. trihalides in the MX3 series (M=N, P, As, Sb or Bi and X=F, Cl, B or I) are known.

(i) Trihalides:

Like the hydrides, the trihalides of group VA have a pyramidal structure in the gaseous state NBr3 and Nl3 are unstable. The instability of halides can be explained on the basis of the small size of the nitrogen atom. Trihalides of N and P are covalent whereas trihalides of Sb and Bi have more ionic, less covalent character. Thus, the covalent character of MX3 decreases on moving from N to Bi.

(ii) Pentahalides:

Nitrogen can not form pentahalides of the type NX5 because nitrogen does not have d-orbitals in its valency shell and can not expand its octet. Phosphorus forms the pentahalides with all the four halogen atoms (F, Cl, Br, and I ), arsenic forms only AsF F5 while antinomy forms SbF5 and SbCl5. On the other hand, bismuth does not give any Penta halide because due to the inert pair effect +3 oxidation state of Bi is more stable than its +5 oxidation state. P, As and Sb form their Penta halides because of the presence of vacant d− orbitals in their valence shell. These pentahalides are trigonal bipyranidal in shape.

(iii) Di element tetra halides :

P, As and Sb also form element tetrahalides of the type M2X4. The halides P2Cl4 and P2Br4 are least well characterized, while P2 F4, P2I4, As2l4, and Sb2l4 are well defined. They all have an X2M−MXX2 type of structure and all are reactive. Diarsenic tetraiodide As2I4 and Sb2l4 decompose on standing to MX3+M.
No Bi2X4 compound is known, but it has long been known that when metallic bismuth is dissolved in molten BiCl3, a black solid of approximate composition BiCl can be obtained.

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