Periodic Table

In-text Questions

Question 8.1.1

What was the number of elements at the time of publication of Mendeleev’s periodic table?

Answer

At the time of publication of Mendeleev’s periodic table, 63 elements were discovered.

Question 8.1.2

State Dobereiner’s law of triads. 

Answer

Dobereiner’s law of triads states that when elements are arranged in the order of increasing atomic masses, the atomic mass of the middle element is roughly equal to the average of the atomic masses of the other two elements, forming a triad.

Question 8.1.3

State Mendeleev’s periodic law. 

Answer

Mendeleev’s periodic law states that the properties of elements are a periodic function of their atomic masses.

Question 8.1.4

Inert gas elements are discovered before or after the publication of Mendeleev’s periodic table.

Answer

Inert gas elements were discovered after the publication of Mendeleev’s periodic table.

Question 8.1.5

State if there are any similarities in properties of subgroup A and B elements of a group.

Answer

The subgroup A elements of a group (also known as representative elements) exhibit similar properties within a group, such as valence electron configuration and reactivity.

Question 8.1.6

Why did Mendeleev place potassium (atomic mass 39) of low atomic mass after argon (atomic mass 40) of higher atomic mass in the periodic table. 

Answer

Mendeleev placed potassium after argon in the periodic table because potassium exhibits similar chemical properties to other Group 1A elements, and placing it in that group maintains the periodicity of properties.

Question 8.1.7

State the Moseley’s periodic law. 

Answer

Moseley’s periodic law states that the properties of elements are a periodic function of their atomic numbers.

Question 8.1.8

Alkaline earth metals are placed in which group? 

Answer

Alkaline earth metals are placed in Group 2A of the periodic table.

Question 8.1.9

What do you mean by the term halogen? In which group they are placed? 

Answer

Halogens are a group of nonmetal elements placed in Group 7A of the periodic table. They are highly reactive and form salts with metals.

Question 8.1.10

Which are noble gases? Why they are called inert gases?

Answer

Noble gases are a group of inert gas elements placed in Group 8A of the periodic table. They are called inert gases because their outermost electron shells are completely filled, making them very stable and unreactive.

Question 8.1.11

What do you mean by periodicity in properties of elements? 

Answer

Periodicity in properties of elements refers to the repeating patterns in the properties of elements as they are arranged in order of increasing atomic number in the periodic table.

Question 8.1.12

Mention one property of the elements which is not periodic in nature.

Answer 

Radioactivity is an example of a property that is not periodic in nature.

Question 8.1.13

Mention some properties of elements which are periodic in nature.

Answer

Some periodic properties of elements include atomic radius, ionization energy, electron affinity, electronegativity, and metallic character.

Multiple Choice Questions (MCQ)

Question 1

The number of elements discovered to date is –

1. 63
2. 109
3. 60
4. 118

Answer

(d) 118

Explanation:

As of 2021, there are 118 confirmed elements in the periodic table. The most recent elements to be added are element 113, Nihonium (Nh), element 115, Moscovium (Mc), element 117, Tennessine (Ts), and element 118, Oganesson (Og).

Question 2

At the time of Publication of Mendeleev’s periodic table, the number of inert gas elements discovered are –

1. 1
2. 3
3. 3
4. 0

Answer

(d) 0

Explanation : 

At the time of publication of Mendeleev’s periodic table, no inert gases had been discovered yet. The discovery of the first noble gas, helium, did not occur until 1895, two years after the publication of Mendeleev’s periodic table.

Question 3

How many periods are there in the Mendeleev’s periodic table –

1. 7
2. 10
3. 6
4. 14

Answer

(a) 7

Explanation : 

There are 7 periods in Mendeleev’s periodic table. The table is arranged in rows and each row is called a period.

Question 4

The similarity between the subgroup A and B elements is with respect to their –

1. Physical properties 
2. Chemical properties 
3. Valency
4. None

Answer

(b) Chemical Properties

Explanation : 

The similarity between the subgroup A and B elements is with respect to their chemical properties. The elements in the same group, also known as the vertical columns of the periodic table, have similar chemical properties because they have the same number of valence electrons, which determines their reactivity and chemical behaviour.

Question 5

The long form of periodic table based on –

1. atomic number
2. atomic mass
3. number of neutrons
4. none of these

Answer

(a) Atomic Number

Explanation:

The long form of the periodic table is based on the atomic number of the elements. The elements are arranged in order of increasing atomic number, which is the number of protons in the nucleus of an atom.

Very Short Answer Type Questions (VSA)

Question 1

State Dobereiner’s low of triads. 

Answer

Dobereiner’s law of triads states that elements with similar chemical properties can be grouped into sets of three, called triads, where the atomic weight of the middle element is approximately equal to the average of the atomic weights of the other two elements.

Question 2

State Mendeleev’s periodic law. 

Answer

Mendeleev’s periodic law states that the properties of the elements are periodic functions of their atomic numbers.

Question 3

Why inert gas elements are placed in group zero? 

Answer

Inert gas elements are placed in group zero because they have a very stable electronic configuration and do not show any tendency to lose, gain, or share electrons to react, i.e., their valency is zero.

Question 4

State Moseley’s periodic law. 

Answer

Moseley’s periodic law states that the properties of the elements vary periodically with their atomic numbers, rather than their atomic weights.

Question 5

Which elements are strong reducing agents?

Answer

Fill up the blanks

1. The second period of the periodic table contains ____ elements. 
2. Halogens are strong ____ agents. 
3. The name of a group 13 element is ____.
4. Along a period from left to right atomic radii ____.
5. The name of a transuranic element is ____.

Answer

Choose the correct word given in brackets

1. The property which is not periodic in nature is ____ (radioactivity / oxidising power) 
2. The covalent radius of atoms is ____ than Vanderwaal’s radius. ( less / higher) 
3. There ____ groups in a long form of the periodic table. ( 18 / 9) 
4. An example of a light metal is ____. (K / Fe) 
5. Group and period number of ₁₉K are ____ and ____. (4 and 2 / 1 and 4)

Answer

Indicate which of the following statements are true and which is false

1. Chlorine is an element of period 2 and group VII A. 
2. ₉₀Th is a transuranic element. 
3. Along a group from top to bottom atomic radii decrease. 
4. Hydrogen and halogens are diatomic non-metallic elements. 
5. lonisation energy of elements along a period from left to right decrease.

Short Answer Type Questions

Question 1

What do you mean by the periodicity of properties of elements? 

Answer

The periodicity of properties of elements refers to the recurring trends and patterns in the chemical and physical properties of the elements as they are arranged in the periodic table.

Question 2

What is the result of Moseley’s experiment and on this basis state the periodic law. 

Answer

Moseley’s experiment showed that the properties of the elements are periodic functions of their atomic numbers. This led to the development of the periodic law, which states that the properties of the elements vary periodically with their atomic numbers.

Question 3

Why alkali metals are placed in Group 1A, why they are named so? 

Answer

Alkali metals are placed in Group 1A because they have a single valence electron that is easily removed to form a univalent cation, and they exhibit similar chemical and physical properties. They are named so because they react readily with water to form alkaline solutions.

Question 4

What do you mean by the term halogen? Mention some properties of these elements. 

Answer

Halogens are a group of nonmetallic elements in Group 7A of the periodic table. They are highly reactive and form compounds with alkali metals and alkaline earth metals. They have a high electronegativity and a tendency to gain electrons to form anions and are diatomic in nature.

Question 5

What is the covalent radius of atoms? 

Answer

The covalent radius of an atom is the distance between the nucleus and the outermost electrons in a covalently bonded molecule.

Question 6

Determine the position of ₉F and ₁₅P in the periodic table. 

Answer

₉F is in the second period and in Group 7A, while ₁₅P is in the third period and in Group 5A of the periodic table.

Question 7

What are transuranic elements, give an example.

Answer

Transuranic elements are elements with atomic numbers greater than 92, the atomic number of uranium. These elements are synthetic, and are produced through nuclear reactions. Examples include plutonium, americium, and curium.

Long Answer (LA) type Questions

Question 1

Describe Mendeleev’s periodic table in short. 

Answer

Mendeleev’s periodic table was one of the earliest attempts to classify elements based on their properties. He arranged the elements in order of increasing atomic weight and noticed that elements with similar chemical and physical properties occurred at regular intervals. He left gaps in his table for elements that were not yet discovered and predicted their properties based on the patterns he observed.

Question 2

Mention the main types of elements and mention the group number to which they belong. 

Answer

The main types of elements are metals, nonmetals, and metalloids. Metals are found in Groups 1A-2A and 3B-12B, nonmetals are found in Groups 4A-8A and metalloids are found along the boundary between metals and nonmetals in Groups 3A and 4A.

Question 3

Describe the reason for the variation of ionic radii along a period. 

Answer

Along a period, the number of electrons in the valence shell remains the same while the nuclear charge increases, causing the effective nuclear charge to increase. This attracts the electrons more strongly, leading to a decrease in ionic radii along a period.

Question 4

Describe with reason how oxidising and reducing properties of elements vary along a period. 

Answer

Along a period, the oxidizing and reducing properties of elements vary due to the change in electronegativity and electron affinity. Non-metals tend to be more electronegative and have a higher electron affinity, making them strong oxidizing agents. Metals tend to be less electronegative and have a lower electron affinity, making them strong reducing agents.

Question 5

What is the atomic radius, mention the types of atomic radius. 

Answer

Atomic radius is the distance from the nucleus to the outermost electron in an atom. There are two types of atomic radius: covalent radius and metallic radius. A covalent radius is half of the distance between the nuclei of two bonded atoms, while a metallic radius is half the distance between the nuclei of two adjacent atoms in a crystal lattice of a metal.

Question 6

Mendeleev violated his periodic law and placed a lower atomic weight ³⁹K after  ⁴⁰Ar had a higher atomic weight. How this placement is justified in the modern periodic table?

Answer

In the modern periodic table, ³⁹K is placed before ⁴⁰Ar because it has a lower atomic number and belongs to the same group (Group 1A) as other alkali metals. This reflects the more important role of atomic number in determining the placement of elements in the periodic table, as compared to atomic weight.