NCERT Class 12 Chemistry Solutions The p Block Elements

NCERT Class 12 Chemistry Solutions The p Block Elements - NCERT Solutions prepared for CBSE students by the best teachers in Delhi. 

class XII Chemistry

Chapter 7 – The p Block Elements 

Question 1:

Discuss the general characteristics of Group 15 elements with reference to their electronic configuration, oxidation state, atomic size, ionisation enthalpy and electronegativity.


General trends in group 15 elements

(i) Electronic configuration: All the elements in group 15 have 5 valence electrons. Their general electronic configuration is ns2 np3.

(ii) Oxidation states: All these elements have 5 valence electrons and require three more electrons to complete their octets. However, gaining electrons is very difficult as the nucleus will have to attract three more electrons. This can take place only with nitrogen as it is the smallest in size and the distance between the nucleus and the valence shell is relatively small. The remaining elements of this group show a formal oxidation state of −3 in their covalent compounds. In addition to the −3 state, N and P also show −1 and −2 oxidation states. All the elements present in this group show +3 and +5 oxidation states. However, the stability of +5 oxidation state decreases down a group, whereas the stability of +3 oxidation state increases. This happens because of the inert pair effect.

(iii) Ionization energy and electronegativity: First ionization decreases on moving down a group. This is because of increasing atomic sizes. As we move down a group, electronegativity decreases, owing to an increase in size.

(iv) Atomic size: On moving down a group, the atomic size increases. This increase in the atomic size is attributed to an increase in the number of shells.


Question 2:

Why does the reactivity of nitrogen differ from phosphorus?


Nitrogen is chemically less reactive. This is because of the high stability of its molecule, N2. In N2, the two nitrogen atoms form a triple bond. This triple bond has very high bond strength, which is very difficult to break. It is because of nitrogen’s small size that it is able to form pπ−pπ bonds with itself. This property is not exhibited by atoms such as phosphorus. Thus, phosphorus is more reactive than nitrogen.


Question 3:

Discuss the trends in chemical reactivity of group 15 elements.


General trends in chemical properties of group − 15

(i) Reactivity towards hydrogen:

The elements of group 15 react with hydrogen to form hydrides of type EH3, where E = N, P, As, Sb, or Bi. The stability of hydrides decreases on moving down from NH3 to BiH3.

(ii) Reactivity towards oxygen:

The elements of group 15 form two types of oxides: E2O3 and E2O5, where E = N, P, As, Sb, or Bi. The oxide with the element in the higher oxidation state is more acidic than the other. However, the acidic character decreases on moving down a group.

(iii) Reactivity towards halogens:

The group 15 elements react with halogens to form two series of salts: EX3 and EX5. However, nitrogen does not form NX5 as it lacks the d-orbital. All trihalides (except NX3) are stable.

(iv) Reactivity towards metals:

The group 15 elements react with metals to form binary compounds in which metals exhibit −3 oxidation states.


Question 4:

Why does NH3 form hydrogen bond but PH3 does not?


Nitrogen is highly electronegative as compared to phosphorus. This causes a greater attraction of electrons towards nitrogen in NH3 than towards phosphorus in PH3. Hence, the extent of hydrogen bonding in PH3 is very less as compared to NH3.


Question 7.5:

How is nitrogen prepared in the laboratory? Write the chemical equations of the reactions involved.


An aqueous solution of ammonium chloride is treated with sodium nitrite. NO and HNO3 are produced in small amounts. These are impurities that can be removed on passing nitrogen gas through aqueous sulphuric acid, containing potassium dichromate.


Students should free download the NCERT solutions and get better marks in exams. panel of teachers recommend students to practice questions in NCERT books and download NCERT solutions.



Click to View or Download pdf file
Click for more Chemistry Study Material

Latest NCERT & CBSE News

Read the latest news and announcements from NCERT and CBSE below. Important updates relating to your studies which will help you to keep yourself updated with latest happenings in school level education. Keep yourself updated with all latest news and also read articles from teachers which will help you to improve your studies, increase motivation level and promote faster learning

Celebration of Republic Day by CBSE

As you are aware, Republic Day is celebrated every year on 26th January to honour the Constitution and Republic of our country. Celebration of this occasion annually helps youth and children of our country to be aware of the significance of Indian Constitution, unity...

BRICS International Online Mathematics Competition

BRICSMATH.COM is an annual International Online Competition in Mathematics, for students of classes I – XII of 07 BRICS countries (Brazil, Russia, India, China and South Africa, Indonesia and Vietnam). The competition is held online on the website and...

Tricks for Utilization of additional time introduced in CBSE Board Exams

Tricks for Proper Utilization of Add-On 15 Minutes introduced in CBSE Board Exams The intend of this article is to share the best suggestions and guidelines to utilize the extra 15 minutes provided for reading the question paper in CBSE Board Examination. These extra...

The CBSE Science Challenge 2020

The CBSE Science Challenge - 2020 Science is inexplicably linked with our lives and helps us to understand the world around us better. Scientific and technological developments contribute to progress and help improve our standards of living. By engaging with this...

Digital Marks Sheets Migration Certificates and Pass Certificates

CBSE pioneered in providing digital academic documents through its academic repository called “Parinam Manjusha” and DigiLocker.  As on now result data from 2004 till this year is available in the repository.  Approx. 12 crores digital academic documents are available...

Studies Today