NCERT Solutions Class 12 Chemistry Chapter 7 The p Block Elements
The p Block Elements is a widely suggested topic for CBSE students of Class 12. The topic has been explained clearly by the experts at Extramarks to enable the students to get an understanding of the various concepts that come under the chapter.
These solutions prepare an excellent approach to master the subject. Also, these solutions answer any concerns regarding the concept by giving in-depth knowledge through study material on p block elements. In addition to NCERT Solutions Class 12 Chemistry Chapter 7, Extramarks provides important questions, question papers examples and sample solution papers.
Key Topics Covered In NCERT Solutions Class 12 Chemistry Chapter 7
The key topics covered in NCERT Solutions Class 12 Chemistry Chapter 7- Solutions include
| Exercise |
Topic |
| 7.1 |
Introduction |
| 7.2 |
Groups 15 elements physical and chemical properties |
| 7.3 |
Dinitrogen preparation |
| 7.4 |
Ammonia preparation |
| 7.5 |
Phosphorus Allotropic forms |
| 7.6 |
Group 16 elements properties |
| 7.7 |
Group 17 elements properties |
| 7.8 |
Group 18 elements properties |
| 7.9 |
FAQ |
Students can refer to the topics under NCERT Solutions For Class 12 Chemistry Chapter 7 by clicking on the respective exercise.
Below is a brief of the various exercises under NCERT Solutions Class 12 Chemistry Chapter 7.
7.1 Introduction
The classification of elements is as per the Periodic Table, and all these elements are further classified into different groups. In this context, we will study more about p block elements. The studies are under Group 15, 16 and 17 elements with a detailed discussion of properties. The study of the elements and processes is applied in wide applications in industries and various other fields. The discussions here will start from the elements such as N, P, As, Sb and Bi. Here, you will study electronegativity, physical and chemical properties, Ionisationenthalpy, and other crucial properties.
This section of NCERT Solutions Class 12 Chemistry Chapter 7 offers a detailed introduction to – p Block Elements as mentioned above. With these solutions, you can now solve exercise problems with much ease. Besides that, you will also be able to understand and revise the concepts better.
p block elements: The elements from groups 13 to 18 in the periodic table are called p-Block elements. In this p block, elements have a valence shell electronic configuration ns2np1–6. Already we have discussed group13 and 14 elements in the previous class.
7.2 Group 15 Elements
Under NCERT Solutions Class 12 Chemistry Chapter 7, we have detailed Group 15 Elements. The group 15 elements have a valence shell electronic configuration as ns2np3. And the element present in these groups is Nitrogen, Phosphorus, Arsenic, Antimony, and Bismuth. The nitrogen element is different from other elements of this group as it is tiny in size. It makes multiple pπ–pπ bonds with itself and highly electronegative atoms. Elements of this group represent a series of properties similarly.
- They show two crucial oxidation states, +5 and +3.
- They interact with halogen, oxygen, and hydrogen.
Group 15 elements are also called elements of the Nitrogen family and include Nitrogen, Phosphorus, arsenic, antimony and Bismuth. The p-block elements are also called the Representative Elements, placed on the right side of the main periodic table.
As conceived by Dimitri Mendeleev, the modern periodic table arranges all the elements known to man based on their atomic number, rare to every element. The conclusion of this arrangement was the periodic table. The elements with the same properties were rearranged into a column known as a group.
Periodic Trends in Group 15 Elements: In Group 15 elements, as you move down a group starting with the lightest element and finishing with the heaviest, you’d notice a general flow in properties as you move down the order.e.g.,, Nitrogen is a gas and non-metal; as you move down the group, we encounter metalloids then, at the bottom, metal, that is Bismuth. More examples are shared in NCERT Solutions Class 12 Chemistry Chapter 7. These trends are shown in the periodic table to help us better understand atoms’ behaviour and allow us to predict new elements.
| Property |
Nitrogen |
Phosphorus |
Arsenic |
Antimony |
Bismuth |
| Atomic symbol |
N |
P |
As |
Sb |
Bi |
| Atomic number |
7 |
15 |
33 |
51 |
83 |
| Atomic mass (AMU) |
14.01 |
30.97 |
74.92 |
121.76 |
209.98 |
| Valence electron configuration |
[He]2s2 2p3 |
[Ne]3s2 3p3 |
[Ar]3d10 4s24p3 |
[Kr]4d10 5s25p3 |
[Xe]4f14 5d106s26p3 |
| Melting point
Boiling point (°C) |
– 210
-196 |
44.15
281 |
817
603(sublimes) |
631
1587 |
271
1564 |
| Density (g/cm3) at 25°C |
1.15(g/L) |
1.8 |
5.7 |
6.68 |
9.79 |
| Atomic radius (pm) |
56 |
98 |
114 |
133 |
143 |
| First, Ionization energy (kJ/mol) |
1402 |
1012 |
947 |
834 |
703 |
| Common Oxidation state(s) |
-3 to +5 |
+5, +3, -3 |
+5, +3 |
+5, +3 |
+3 |
| Ionic radius (pm) |
146(-3) |
212(-3) |
58(+3) |
76(+3) |
103(+3) |
| Electronegativity |
3.0 |
2.2 |
2.2 |
2.1 |
1.9 |
Some of the modern periodic table trends for group 15 elements of the p-Block are shown below. The same has been explained in detail in NCERT Solutions Class 12 Chemistry Chapter 7 study material.
Electronic Configuration
- The valence shell electronic configuration plays a significant role in how an element performs. The electronic configuration of group 15 elements is ns2np3.
- In group 15, all elements have the same arrangement, so they’re similar.
- The s-orbital in this group is filled, and the p-orbitals are half-filled, making their configuration extra stable.
Atomic and Ionic Radii
- When you see the electronic configuration of elements in the table below, you will observe that new orbitals are added to the atom with every step you move downwards.
- This addition of new orbitals will increase both the atomic and the ionic radii of group 15 elements.
- However, from Arsenic to Bismuth, only a tiny increase in ionic radius is observed.
- Filled d and f orbitals in heavier members.
Ionization Enthalpy
- is the amount of energy required to eliminate an electron from the outermost orbit of the atom.
- Ionisation enthalpy measures how difficult the nucleus is carrying on to the electron.
Electronegativity
- The value decreases down the group with the increasing atomic size.
- Due to an increase in distance between the nucleus and the valence shell as we move down the group.
Physical properties
- All the elements of the group survive in a polyatomic state.
- The first, Nitrogen, is gas; however, as you go down, there is a remarkable increase in the metallic character of the Nitrogen element.
- Nitrogen and Phosphorus are non-metals, Arsenic and Antimony are metalloids, and Bismuth is a metal.
- Except for Nitrogen, all the other elements have allotropes.
Chemical Properties
- The valence shells of the p block elements have an electronic configuration of ns2 np3.
- So the p block elements here can either lose 5 electrons or gain 3.
- The standard oxidation states of these elements are -3, +3, and +5.
- With a decrease in the Ionization enthalpy and electronegativity, therefore, to the increasing atomic radius, the tendency to gain 3 electrons to create a -3 oxidation state decreases down the group.
- Bismuth hardly forms any compound with a -3 oxidation state.
- As we move down, the stability decreases by +5 and that of +3 increases due to the inert pair effect.
7.3 Dinitrogen, N2:
Under NCERT Solutions Class 12 Chemistry Chapter 7, students learn about the following.
Preparation: Air’s liquefaction and fractional distillation produce commercial dinitrogen when N2 distils out of the first (b.p.=77.2K).
Laboratory Method:
NH4Cl (aq) + NaNO2 (aq) → N2 (g) + 2H2O (l) + NaCl (aq)
Very pure nitrogen can be collected by the thermal decomposition of sodium and barium azide solution.
Properties: Dinitrogen is colourless, odourless, without taste and non-toxic gas. It has two stable isotopes: 14N and 15 N. It has very less solubility in water.
As of the high bond enthalpy of N ≡ N, dinitrogen is rather inert at room temperature. At high temperatures, it directly combines with some metals to form primarily ionic nitrides and, with non-metals, covalent nitrides.
7.4 Ammonia Preparation:
In this section of NCERT Solutions Class 12 Chemistry Chapter 7, students learn about ammonia preparation. On a large scale, Ammonia is manufactured by Haber’s process:
N2 (g)+ H2 (g) 3(g)
On a small scale, Ammonia is obtained from ammonium salts which decompose when treated with caustic soda or lime
2NH4Cl + Ca(OH)2—2NH3 +2H2O + CaCl2
Properties: Ammonia gas is a colourless gas with a pungent smell. Its freezing and boiling points are 198.4 and 239.7 K, respectively.
7.5 Phosphorus Allotropes
Phosphorus is formed in many allotropic forms. The important ones are white, red and black. In this section of NCERT Solutions Class 12 Chemistry Chapter 7, students are given more details on Phosphorus allotropes.
- White Phosphorus: It’s a translucent white waxy solid. It is poisonous, not soluble in water, but soluble in CS2 and glows in the dark (Chemiluminescence). This White Phosphorus consists of discrete tetrahedral molecules.
- Red Phosphorus is generated by heating white Phosphorus at 573 K in an inert atmosphere for several days. It is less reactive than White Phosphorus. It is polymeric, consisting of P4 tetrahedral linked together.
- Black Phosphorus has two forms α-black Phosphorus and β-black Phosphorus. α-Black Phosphorus is obtained when red Phosphorus is heated in a sealed tube at 803 K. It can be sublimed in air and has opaque monoclinic or rhombohedral crystals. It does not oxidise in the air. β-Black Phosphorus is prepared by heating white Phosphorus at 473 K under high pressure. It does not burn in the air up to 673 K.
7.6 Group 16 Elements
The elements of group 16 have an electronic configuration of ns2np4 and have a maximum oxidation state of +6. It has varying chemical and physical properties. The preparation of dioxygen in the laboratory is carried out by heating KClO3 with a MnO2 catalyst.
Students may understand the clear concept of p blocks elements by referring to NCERT solutions class 12 chemistry chapter 7.
7.7 Group 17 Elements
Under Exercise 7.7 of NCERT Solutions Class 12 Chemistry Chapter 7, students learn about group 17 elements. The elements of group 17 are found only in the combined state and are highly reactive. The elements that belong to this group are Fluorine, Chlorine, Bromine, Iodine, and Astatine. Their highest oxidation state is +7, whereas the common oxidation state is -1.
7.8 Group 18 Elements
The elements of group 18 are noble gases. Their valence shell electronic configuration except Helium is ns2np6. The electronic configuration of He is 1s2. All the noble gases except radon occur in the atmosphere.
Exercise 7.9 includes frequently asked questions that students may benefit from. Students may refer to NCERT solutions class 12 chemistry chapter 7 study material provided by Extramarks while preparing for their examination.
NCERT solutions class 12 chemistry chapter 7 Exercise & Answer Solutions
NCERT solutions class 12 chemistry chapter 7 is explained in detail by the experts of Extramarks. Students can benefit from the detailed solutions provided by the experts. The Solutions cover all the concepts that fall under Chapter 7, The p Block Elements, such as Dinitrogen preparation, Phosphorus Allotropic forms, Dinitrogen preparation, Group 16 elements properties and more. Students may refer to Extramarks NCERT solutions class 12 chemistry chapter 7 by registering on the website.
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