MG SCHOOL EDUCATION: Class 10 Science Chapter 5 Periodic classification of elements

Class 10 Science

Chapter 5 Periodic classification of elements

Previous years appeared questions

Multiple Choice Questions

1. Atomic number of chlorine is 17. The period number of this element in modern periodic table is (March 2022)

(A) 2 (B) 7 (C) 4 (D) 3

Ans. : (D) 3

2. The atomic numbers of elements A, B, C and D are 3, 9, 4 and 8 respectively. Elements having metallic nature among these are (Sep 2020)

(A) B and D (B) A and B

Ans. : (C) A and C

3. The number of groups and periods in the modern periodic table respectively, are (June 2019)

(A) 7 and 9 (B) 18 and 7

Ans: (B) 18 and 7

4. In modern periodic table, as we move from left to right along the period, the atomic size of the elements. (KSEEB MQP 2020)

A. increases

B. does not change

C. decreases

D. first increases and then decreases

Ans: C. decreases

One Marks Questions

1. State the modern periodic law. ( june 2022) (March 2022)

Ans. : ‘The properties of elements are periodic functions of their atomic numbers.’

2. Sodium and potassium are placed in the same group of modern periodic table. If the molecular formula of sodium sulphate is Na2SO4, then decide the molecular formula of potassium sulphate. Give reason for your answer. (March 2020)

Ans. :

> Molecular formula of potassium sulphate is K2SO4.

> Because both sodium and potassium have same number of valence electrons.

3. State Newlands’ law of octaves. (MQP 2021)

Ans:

Newlands’ law of octaves State that 'When elements are arranged in the increasing order of atomic masses, the properties of every eighth element are similar to the first.'

4. in the modern periodic table, the elements of 17th group are Flourine, Chlorine, Bromine, Iodine respectively. Which element has the highest ability to receive electrons? Why (KSEEB MQP 2020)

Ans:

Fluorine, because fluorine is smaller and has its electrons closer to the positively charged nucleus. So that fluorine has more tendency to attract shared electrons to itself.

Two Marks Questions

1. How are the limitations of Mendeleev’s periodic table rectified in the modern periodic table ? (Sep 2020)

Ans. :

Limitations of Mendeleev’s classification :

No fixed position was given to hydrogen
No fixed position was given to isotopes of all elements
The atomic masses from one element to the other do not increase in a regular manner
It is not possible to predict how many elements could be discovered between two elements.

2. How does the atomic size vary in groups and periods of the modern periodic table ? Why ? (Sep 2020)

Ans:

Atomic size increases down the group.
Because new shells are being added as we go down the group, this increases the distance between the outermost electrons and the nucleus.
The atomic size decreases on moving from left to right along a period.
Because an increase in nuclear charge tends to pull the electrons closer to the nucleus.

3. The position of elements A, B, C, D in the modern periodic table is given in the following table. Answer the following questions by observing the table :

(i) Which element has the highest atomic size ? Why ?

(ii) Which element has the least metallic property ? Why ? (June 2019)

Ans:

(i) C has highest atomic size since atomic size increases down a group and decreases along a period from left to right.

(ii) B has least metallic property since metallic property increases down a group and decreases along a period.

4. State modern periodic law. Name the elements of first period in the modern periodic table. (June 2019)

Ans:

> ‘The properties of elements are periodic functions of their atomic numbers.’

> The first period elements are Hydrogen and Helium.

Three Marks Questions

1. Write the two reasons for placing oxygen and sulphur in a same group of modern periodic table. Which one of these elements has larger atomic size and why ? [ Atomic number of oxygen = 8, Atomic number of sulphur = 16 ] ( june 2022)

Ans. :

They have same chemical properties.
They have same valence electrons / they have similar electronic configuration in outermost shell.
Sulphur has larger atomic size because atomic size increases down the group / New shells are being added as we go down the group. This increases the distance between outermost electron and the nucleus.

2. Write the limitations of Mendeleev’s periodic table. Why is silicon called metalloid ? ( june 2022)

Ans. :

Limitations of Mendeleev’s classification :

No fixed position was given to hydrogen
No fixed position was given to isotopes of all elements
The atomic masses from one element to the other do not increase in a regular manner
It is not possible to predict how many elements could be discovered between two elements.

Silicon is called metalloid because it exhibits some properties of both metals and non-metals.

3. What is atomic size ? In the modern periodic table the atomic size decreases along a ‘period’ and increases down the ‘group’. Why ? Explain. (March 2022)

Ans. :

The distance between the centre of the nucleus and the outermost shell of an isolated atom.
In modern periodic table atomic size decreases along the period because Electrons are being added to the outermost shell of an atom that tends to pull the electrons closer to the nucleus / No new shells are added to atom.
Atomic size increases down the group because New shells are being added, this increases the distance between the outer most electrons and the nucleus.

4. The atomic numbers of two elements are 8 and 16 respectively. Write the electronic configuration of these two elements. Do you keep these two elements in the same group of the modern periodic table ? Justify your answer. Find out which of these two elements is more electronegative. Give reason for your answer. (March 2020)

Ans. :

> Atomic number 8 — 2, 6

> Atomic number 16 — 2, 8, 6

> Yes, these two elements belong to the same group.

> Because in the outer most shell they have same number of electrons or both have same number of valance electrons.

> Element with atomic number 8 is more electronegative than the element with atomic number 16.

> Electronegativity decreases down the group.

5. Observe the given table and answer the following question : (March 2019)

Identify the two elements that belong to the same period and the two elements that belong to the same group. Give reason for your conclusion.

Ans:

> Element B and element D are in same period because their atoms have two shells.

> Element A and element E are in the same group because their outermost shell has one electron.

6. The atomic numbers of two elements are 12 and 16 respectively. Do you keep these two elements in the same period of the modern periodic table? Justify your answer. Which one of these two elements is more electropositive? Why? (KSEEB MQP 2021)

Ans:

atomic number 12 = Mg

atomic number 16 = S

both of these elements come inside same period that is 3rd period .

electro - negativity generally increases as you move from left to right across a period so Sulphur will be more electronegative than magnesium hence magnesium is more electropositive

7. Explain the limitations of Medeleev’s periodic table. (KSEEB MQP 2020)

Ans:

Limitations of Mendeleev’s classification :

No fixed position was given to hydrogen
No fixed position was given to isotopes of all elements
The atomic masses from one element to the other do not increase in a regular manner
It is not possible to predict how many elements could be discovered between two elements.

8. Explain the limitations of Newlands’ law of Octaves. (KSEEB MQP 2020)

Ans:

Law of Octaves only applicable upto calcium and after calcium every 8th did not possess properties similar to that of the first.
later on , several new elements were discovered, whose properties did not fit into the aw of octaves
Newlands'law of Octaves worked well with lighter elements only.