CBSE Important Questions for Class 11 Chemistry Classification of Elements and Periodicity in Properties - 2025-26

1 Marks Questions

1. How many elements are known at present?

Ans: At present 114 elements are known to us.

2. Who was the first scientist to classify elements according to their properties?

Ans: In the year 1829, a German scientist named Johann Dobereiner was the first one who classified elements according to their properties.

3. What is the basis of the triad formation of elements?

Ans: Triad formation is basically dependent upon the middle element which represents that the atomic weight of the middle one is the half of the other two elements of the triad which are in between these two elements and this relationship is also given by Dobereiner know as the law of triads.

4. State the modern ‘Periodic law’?

Ans: Elements are arranged according to their physical and chemical properties and with the increase in atomic numbers.

5. Define and state Mendeleev’s periodic law.

Ans: This law states that elements are arranged according to their atomic weight.

6. Give the general characteristics of the long form of the Modern periodic table?

Ans: General characteristics of the long form of Periodic table can be discussed as follows:

1. 18 vertical columns known as groups.

2. Their groups are numbered from left to right as 1-18.

3. Seven horizontal rows are known by the name periods.

4. The elements present in groups 1, 2 and 13-17 are called main group elements.

5. The elements present in groups 3-12 are called transition elements.

7.  In short, give the features of the seven periods.

Ans: The first period is said to be the shortest period containing only two elements hydrogen and helium. 

The second and third periods both contain 8 elements from lithium to neon in the second period while from sodium to argon in the third period. 

The fourth and fifth periods both contain 18 elements from potassium to krypton in the fourth and rubidium to xenon in the fifth period; these are long periods. 

The sixth period contains 32 elements starting from caesium and the last one is radon and is said to be the longest period.

The seventh period is incomplete; it starts with francium having atomic number 87 and up to 93 onwards are purely synthetic in nature and are called transuranium elements.

8. Define electronic configuration.

Ans: Electronic configuration defines how electrons are distributed into orbitals of an atom.

9. What is the electronic configuration when elements are classified group-wise?

Ans: Those elements which are in the same group have the same number of valence electrons and also show similar physical and chemical properties.

10. Predict the position of the element in the periodic table satisfying the electronic configuration $(n-1){{d}^{1}}n{{s}^{2}}$ for n=4.

Ans: Put the value of n = 4 in the general equation $(n-1){{d}^{1}}n{{s}^{2}}$ i.e. $(4-1){{d}^{1}}n{{s}^{2}}=3{{d}^{1}}n{{s}^{2}}$

3d group elements lies in fourth period and in III B group.

11. How does atomic size change in a group?

Ans: It Goes on increasing while we move down the group.

12. Why do Li and Mg show resemblance in chemical behaviour?

Ans: As these are diagonally related to each other so they show similar chemical behaviour.

13. The atomic radius of elements decreases along the period but Neon has the highest size among III period elements? Why?

Ans: Neon contains Vander Waal radius while all other elements contain covalent radius and Vander wall radius have greater value as compared to covalent so we can say Neon has the highest size.

14. Define valency.

Ans: Valency is defined as the combining capacity of an element.

15. How does valency vary in a group and period in the periodic table?

Ans: Valency remains constant in a group and increases while moving in a period from left to right.

16. What is the valency of noble gases?

Ans: Valency acquired by noble gases is zero.

17. How do metals react in a period?

Ans: Reactivity resembles the property by which an element loses an electron while moving in a period from left to right reactivity decreases due to a decrease in size.

18. How do metals react in a group?

Ans: Reactivity resembles the property by which an element loses an electron while moving down a group reactivity increases due to an increase in size.

19. What is amphoteric oxide?

Ans: Oxides that can behave as acids, as well as bases, are known as amphoteric oxides.

20. Define a neutral oxide.

Ans: Neutral oxides are those oxides that have neither show acidic nor basic properties.

21. What is the general outer electronic configuration of f – block elements?

Ans: The general outer electronic configuration of f – block elements is shown in this way $(n-2){{f}^{1-14}}(n-1){{d}^{0-10}}n{{s}^{2}}$.

22. Why do Na and K have similar properties?

Ans: Na and K show similar properties as they contain the same number of valence electrons.

23. Arrange the following elements in the increasing order of metallic character: Si, Be, Mg, Na, P.

Ans: P > Si > Be > Mg > Na 

2 Marks Questions

1. How did Mendeleev arrange the elements?

Ans: Mendeleev arranged elements in the form of a table which contains horizontal rows and vertical columns and elements are arranged in these columns and rows according to their atomic weight in an increasing manner and arrangement is in such a way that the elements having similar properties are in the same vertical column or group.

2. Name the two elements whose existence and properties were predicted by Mendeleev though they did not exist then.

Ans: Gallium and Germanium are two elements whose existence as well as some physical properties were also explained by Mendeleev though they did not exist at that time.

3. Give the main features of s-block elements.

Ans: Those elements whose last electron will enter in the s subshell which is its outermost energy shell are called s-block elements. It contains only two elements named hydrogen and helium. The general configuration of s-block elements is $n{{s}^{1-2}}$ as s subshell can acquire a maximum of 2 electrons.

4. Give the main features of p-block elements.

Ans: Those elements whose last electron will enter the p subshell which is its outermost energy shell are called p-block elements. It contains elements of groups 13-18. The general configuration of p-block elements is $n{{s}^{2}}n{{p}^{1-6}}$, p subshell can contain maximum 6 electrons.

5. Give the main features of d-block elements.

Ans: Those elements whose last electron will enter in the d subshell which is its outermost energy shell are called d-block elements. d block elements are generally present between the s and p block elements. It contains elements of groups 3-12. The general configuration of d-block elements is $(n-1){{d}^{1-10}}n{{s}^{1-2}}$, d subshell can contain maximum 10 electrons.

6. Give the main features of f-block elements.

Ans: Elements whose last electron will enter in the f subshell which is its outermost energy shell are called f-block elements. The elements of f-block elements are present below the periodic table in the form of two lines. The general configuration of f-block elements is $(n-2){{f}^{1-14}}(n-1){{d}^{0-1}}n{{s}^{2}}$, f subshell can contain maximum 14 electrons.

7. Explain why cations are smaller and anions are larger in radii than their parent atom?

Ans: The radius of cation is smaller as compare to its parent atom as we know that cation is formed by the loss of one or more electrons from the gaseous atom during the nuclear charge of the atom remains the same. During this process nuclear holds the remaining electrons more tightly this can be explained due to the increase in effective nuclear charge per electron this increase is due to a decrease in size.

Anion is formed by the gain of one or more electrons by the gaseous atom and nuclear charge also remains the same in this case although the number of electrons goes on increasing. The effective nuclear charge per electron decreases in the case of anion which makes the firmness of atoms with nucleus a little low as this will increase its size.

8. Define ionization enthalpy and electron gain enthalpy.

Ans: Ionization enthalpy: It generally represents the energy that is required to remove an electron from an isolated gaseous atom in the ground state which further gives us protons i.e. form a positive ion. The reaction can be shown as:

$X(g)+Energy\to {{X}^{+}}(g)+{{e}^{-}}$

Electron gain enthalpy: The change in enthalpy accompanying during the process is defined in which an electron is gained by any neutral gaseous atom and it converts that atom into a negative ion is known as electron gain enthalpy. The reaction of this can be shown as:

$X(g)+{{e}^{-}}\to {{X}^{-}}(g)$

9. How does metallic character change in a group?

Ans: While moving down the group metallic character increases.

10. The size of an atom can be expressed by three radii. Name them. Which of these given the highest, and the lowest value of the atomic radius of an element?

Ans: The atomic size is generally expressed in terms of three main radii known as covalent radius, metallic radius and Van der Waal’s radius. The order of these three radii will be Van der Waal’s radius > Metallic radius > covalent radius.

11. Among the elements B, Al, C and Si

(a) Which has the highest first ionization enthalpy?

Ans: Highest first ionization enthalpy is shown by C (carbon).

(b) Which has the largest atomic radius?

Ans: Al (Aluminium) has the largest atomic radius as compared to others.

12. $N{{a}^{+}}$ has a higher value of ionization enthalpy than Ne, though both have the same electronic configuration.

Ans: $N{{a}^{+}}$ and Ne both contains 10 electrons but the number of protons is different as in $N{{a}^{+}}$ 11 protons are present which exert higher effective nuclear charge and the tendency of removing an electron is quite difficult as compare to Ne as it has only 10 protons. 

13. How does the reactivity of non–metals change in a period and group?

Ans: Reactivity generally represents the property of non-metals which measures its tendency to gain electrons. Reactivity of non-metals increases while moving in a period due to a decrease in size while decreases moving down the group due to an increase in size.

14. Give the properties of the oxides in a particular period.

Ans: Oxides are those elements that are capable of combining with oxygen atoms. The normal oxide is generally formed by those elements which are on the extreme left and most basic in nature example $N{{a}_{2}}O$ whereas those oxides which formed on the extreme right are of acidic nature example $C{{l}_{2}}{{O}_{7}}$ and the oxides which form in the middle position are of amphoteric nature like $A{{l}_{2}}{{O}_{3}}$ or neutral in nature example $CO$.

15. Why does lithium form a covalent bond, unlike another alkali which forms an ionic bond?

Ans: Lithium forms a covalent bond which is different from other group members this type of anomalous behaviour of Li can be explained on the basis of its small size, large charge/radius ratio and has high electronegativity value. Orbital available for bonding of Li is given as $1{{s}^{2}}2{{s}^{1}}$.

16. The atomic number of an element is 16. Determine its position in accordance with its electronic configuration.

Ans: Electronic configuration of an element having atomic number 16 is given by 1s22s22p63s23p4 as we can see that the last electron will enter into p subshell and said to be p block element and placed in the third period and 16th group of the periodic table.

17. Why are elements at the extreme left and extreme right the most reactive?

Ans: The maximum chemical reactivity at the extreme left which is present among alkali metals can be exhibited due to the loss of an electron which leads to the formation of a cation due to its low ionization enthalpy and at the extreme right where halogens are present which is shown by the gain of an electron forming an anion due to its high electron affinity.

18. Why does the ionization enthalpy gradually decreases in a group?

Ans: Ionization enthalpy gradually decreases while moving down a group due to an increase in its atomic and ionic radii.

19. Why does the electronegativity value increases across a period and decreases down a period?

Ans: Electronegativity value generally corresponds with the attraction between outer electrons and the nucleus which increases with the decrease in atomic radius along a period and in this case electronegativity value also increases. In a similar manner electronegativity value decreases with the increase in atomic radii as we move down a group.

20. How do electronegativity and non – metallic characters related to each other?

Ans: Electronegativity is directly related to the non – metallic character of elements while in the case of metallic properties it is inversely related. Thus the increase in electronegativity’s across a period is defined by an increase in non – metallic properties of elements and the decrease in electronegativity by moving down a group is defined by a decrease in its non – metallic properties of elements.

21. Describe the main features of Mendeleev’s periodic table?

Ans: 

1. Mendeleev table is discovered by the scientist Mendeleev in which the elements were arranged in vertical columns and horizontal rows. The vertical columns are called groups while the horizontal rows are called periods.

2. Total there are eight groups in this table represented as Group I to VIII. The group numbers were designed with Roman numerals. 

3. There are seven periods which accommodate more elements and the period 4, 5, 6 and 7 are further divided into two halves. The first half of the elements are placed in the upper left corner and the second half in the lower right corner of each box.

Important Questions of Chapter 3 Chemistry Class 11 Free PDF Download

Class 11 chemistry paper is for 70 marks and the rest 30 marks are for your practical examination. To score well in the examination will require a clear and logical understanding of each chapter. It is advisable to practice all the questions from your NCERT textbook and chemistry chapter 3 class 11 important questions pdf. Using both of these in combination will improve your knowledge of the subject and the score for the same.

The class 11 Chemistry syllabus is divided into 14 chapters in total. The weightage marks of each chapter are given below. Chapter 3- Classification of Elements and Periodicity in Properties has a weightage of 4 marks which implies you can find very short answer type and short answer type questions from this chapter.

The Types of Questions Asked in the Examination and Their Weightage is Given Below

• Very Short Answer type Questions: 20 questions X 1 mark

• Short Answer type I Questions: 7 questions X 2 marks

• Short Answer type II Questions: 7 questions X 3 marks

• Long Answer type Questions: 3 questions X 5 marks

Classification of Elements and Periodicity in Properties Class 11 Important Questions

The list of important questions of ch 3 chemistry class covers the entire chapter. Practising these questions will also improve your understanding of the chapter. The subtopics included in the chapter- Classification of Elements and Periodicity in Properties are as follows.

• Modern periodic law

• The present form of the periodic table 

• Periodic trends in properties of elements 

1. Atomic radii

2. Ionic radii 

3. Inert gas radii

4. Ionization enthalpy

5. Electron gain enthalpy

6. Electronegativity

7. Valency 

• Nomenclature of elements with atomic number greater than 100

Let Us Look at These Topics in Detail:

Modern Periodic Law

According to modern periodic law, the physical and chemical properties of the elements in the periodic table are periodic functions of the number of protons or the atomic number. The elements are arranged in the order of increasing atomic numbers and it is observed that the elements exhibit similar properties after regular intervals.

Mendeleev’s Approach for periodic Law- The law suggested that the properties of the elements are a function of their atomic mass. Mendeleev was the first person to categorize the elements in a table and it was his studies and findings that paved the way for the modern-day periodic table. 

The Modern or Long Form of Periodic Table

The modern form of the periodic table follows the modern periodic law that the properties of the elements are the function of the atomic number. It consists of 18 vertical columns and 7 horizontal rows in total. 

• The vertical columns represent the 18 groups numbered from 1 to 18. Each element in the group has the same outer shell electronic configuration.

• The seven horizontal rows represent the different periods from 1 to 7. Each period represents the number of shells present in the atom of the element. 

• The cause of periodicity in the modern periodic table is the similar outer shell electronic configuration after regular intervals.

Periodic Trends in Properties of Elements

• Atomic Radii - Atomic radii is the distance between the nucleus of the atom to the surrounding shell of electrons. Typically, atomic radius is the measure of the size of the atoms of the element. The atomic radius decreases as we move towards periods and increases as we go down the group.

• Ionic Radii - It is the distance between the nucleus and the electron in the outermost shell of an ion. It follows the same trend as that of the atomic radii, increases as we go down the group, and increases as we move across a period. This only applies if the ions of the elements are the same, either cation or anion.

• Inert Gas Radii - Inert gases have the highest radius in a period. Usually, the radius decreases as we move across a period but it increases in the case of noble gases. It is because inert gases do not form any covalent bonds and only a weak Van der Waals force of attraction is present, which increases the radii of the noble gases.

• Ionization Enthalpy - It is defined as the energy required to remove an electron from the outermost shell. The ionization enthalpy increases due to the increase in atomic radii and decreases as we move down the group as the number of shells increase and the force of attraction on the outermost electron decreases.

• Electron Gain Enthalpy -  It is the amount of energy released when an electron is added to the outermost shell of an atom in the gaseous state. The electron gain enthalpy increases on moving across the periodic table and decreases as we go down the group.

• Electronegativity - It is defined as the tendency of an atom to attract a shared pair of electrons. Electronegativity increases when we move towards the period as the atomic size decreases and nuclear charge increases. As we go down the group, the nuclear charge increases but they are accompanied by the increase in the number of shells, therefore electronegativity decreases.

• Valency - The number of electrons lost or gained by an atom to obtain a stable state is defined as the valency of the atom. Valency remains the same as we go down the group, but in the case of the period, it first increases and then decreases.

List of Important Questions of Ch 3 Chemistry Class 11

Given below are some of the commonly asked questions from the chapter- Classification of Elements and Periodicity in Properties. These will give you a brief about what type of questions are included in the important questions of chapter 3 chemistry class 11 pdf and often asked in the examinations. Practice these questions well to get a better understanding of the examination pattern. 

• Why does the need to classify the elements arise?

• Differentiate between Mendeleev’s periodic table and the modern periodic table.

• How are the elements with atomic numbers above 100 named?

• Explain the various trends observed in the periodic table.

• Differentiate between atomic radius and ionic radius.

• What is the reason for the smaller cation size and larger anion size of the same parent atom?

• Explain electron gain enthalpy and ionization enthalpy.

• Discuss valency and the variation in its trends.

Benefits of Class 11 Chemistry Chapter 3 Important Questions

All the important topics of Chapter 3 are covered in the Classification of elements and periodicity in properties class 11 important questions pdf. These topics are fundamental to the studies of chemistry and you will learn about them in detail in higher studies. It is therefore advisable to move forward with a firm foundation and the pdf will aid you in just that. 

The benefits of using class 11 chemistry chapter 3 important questions pdf are as follows:

• The list of questions is prepared as per the previous year question papers and the exam pattern.

• The pdf is prepared by our subject experts at Vedantu after thorough research.

• The pdf serves as a great revision tool allowing you to revise all the important questions and concepts from the chapter.

• The list of important questions will test your understanding of the same and help in highlighting your weaker sections.

• The pdf is prepared as per the CBSE guidelines to help you score well in your examinations.

Conclusion

The pdf of chemistry chapter 3 class 11 important questions is a must-have tool in your preparation toolkit. These questions are arrived at after thorough research. The study material provided at Vedantu is accurate and reliable as subject experts prepare them. Download the free pdf and kickstart your preparations for your final examinations.

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CBSE Class 11 Chemistry Chapter-wise Important Questions

CBSE Class 11 Chemistry Chapter-wise Important Questions and Answers cover topics from all 9 chapters, helping students prepare thoroughly by focusing on key topics for easier revision.

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